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diff --git a/32855-8.txt b/32855-8.txt new file mode 100644 index 0000000..833b15c --- /dev/null +++ b/32855-8.txt @@ -0,0 +1,3410 @@ +The Project Gutenberg EBook of Natural History of the Bell Vireo, Vireo +bellii Audubon, by Jon C. Barlow + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Natural History of the Bell Vireo, Vireo bellii Audubon + +Author: Jon C. Barlow + +Release Date: June 17, 2010 [EBook #32855] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE BELL VIREO *** + + + + +Produced by Chris Curnow, Joseph Cooper and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + + + + UNIVERSITY OF KANSAS PUBLICATIONS + MUSEUM OF NATURAL HISTORY + + Volume 12, No. 5, pp. 241-296, 6 figs. + March 7, 1962 + + Natural History of the Bell Vireo, + Vireo bellii Audubon + + BY + JON C. BARLOW + + UNIVERSITY OF KANSAS + LAWRENCE + 1962 + + + + + UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY + + Editors: E. Raymond Hall, Chairman, Theodore H. Eaton, Jr., + Henry S. Fitch + + Volume 12, No. 5, pp. 241-296, 6 figs. + Published March 7, 1962 + + UNIVERSITY OF KANSAS + Lawrence, Kansas + + + PRINTED BY + JEAN M. NEIBARGER, STATE PRINTER + TOPEKA, KANSAS + 1962 + + 29-1506 + + + + +Natural History of the Bell Vireo, +Vireo bellii Audubon + +BY + +JON C. BARLOW + + + + +CONTENTS + + + PAGE + CONTENTS 243 + INTRODUCTION 245 + ACKNOWLEDGMENTS 245 + METHODS OF STUDY 246 + STUDY AREA 247 + Considerations of Habitat 248 + SEASONAL MOVEMENT 250 + Arrival in Spring 250 + Fall Departure 251 + GENERAL BEHAVIOR 252 + Flight 252 + Foraging and Food Habits 252 + Bathing 253 + VOCALIZATIONS 254 + Singing Postures 255 + Flight Song 255 + Daily Frequency of Song 255 + Types of Vocalizations 255 + TERRITORIALITY 258 + Establishment of Territory 259 + Size of Territories 259 + Permanence of Territories 260 + Maintenance of Territory 260 + Aggressive Behavior of the Female 264 + Interspecific Relationships 264 + Discussion 265 + COURTSHIP BEHAVIOR 267 + Displays and Postures 268 + Discussion 270 + SELECTION OF NEST-SITE AND NESTBUILDING 272 + Building 274 + Gathering of Nesting Materials 276 + Length and Hours of Nestbuilding 277 + Abortive Nestbuilding Efforts 277 + Renesting 277 + The Nest 277 + EGGLAYING AND INCUBATION 278 + Egglaying 278 + Clutch-size 279 + Incubation 280 + The Roles of the Sexes in Incubation 280 + Relief of Partners in Incubation 283 + NESTLING PERIOD 283 + Hatching Sequence 283 + Development of the Nestlings 284 + Parental Behavior 285 + Feeding of the Nestlings 286 + Nest Sanitation 287 + Fledging 287 + Nest Parasites 287 + FLEDGLING LIFE 288 + Second Broods 288 + REPRODUCTIVE SUCCESS 289 + Behavior 290 + Predation 291 + Cowbird Parasitism 291 + SUMMARY 292 + LITERATURE CITED 294 + + + + +INTRODUCTION + + +The Bell Vireo (_Vireo bellii_ Aud.) is a summer resident in riparian +and second growth situations in the central United States south of +North Dakota. In the last two decades this bird has become fairly +common in western, and to a lesser extent in central, Indiana and +is apparently shifting its breeding range eastward in that state +(Mumford, 1952; Nolan, 1960). In northeastern Kansas the species +breeds commonly and occurs in most tracts of suitable habitat. + +The literature contains several reports dealing exclusively with the +Bell Vireo, notably those of Bennett (1917), Nice (1929), Du Bois +(1940), Pitelka and Koestner (1942), Hensley (1950) and Mumford +(1952). Bent (1950) has summarized the information available on the +species through 1943. Nolan (1960) recently completed an extensive +report based on a small, banded population at Bloomington, Monroe +County, Indiana. He validated for this species many points of natural +history previously based on estimates and approximations, especially +concerning the post-fledging life of the young and the movement of the +adults from one "home range" to another in the course of a single +season. + +None of these reports, however, has emphasized the ritualized +behavioral patterns associated with the maintenance of territory and +with courtship. Among the North American Vireonidae, the behavior of +the Red-eyed Vireo (_Vireo olivaceus_) is best documented (Sutton, +1949; Lawrence, 1953; Southern, 1958). With this species authors have +concentrated on the mechanics of the breeding season and their reports +contain little discussion of the aggressive and epigamic behavior of +the bird. + +The amount of information on the ritualized behavior of the Bell Vireo +and related species heretofore has been meager. I observed breeding +behavior from its inception in early May through the summer of 1960. +It is hoped the resulting information will serve as a basis of +comparison in future studies of behavior of vireos; such ethological +data are becoming increasingly important, especially as an aid in +systematics. + + + + +ACKNOWLEDGMENTS + + +To professors Frank B. Cross, Henry S. Fitch, and Richard F. Johnston +of the Department of Zoology of the University of Kansas I am grateful +for comments and suggestions in various phases of the study and the +preparation of the manuscript. Professor Johnston also made available +data on the breeding of the Bell Vireo from the files of the Kansas +Ornithological Society. I am indebted to my wife, Judith Barlow, for +many hours of typing and copy reading. Mrs. Lorna Cordonnier prepared +the map, Thomas H. Swearingen drew the histograms, and Professor A. B. +Leonard photographed and developed the histograms. Dr. Robert M. +Mengel contributed the sketch of the Bell Vireo and George P. Young +prepared the dummy Bell Vireo used in the field work. Thomas R. +Barlow, Donald A. Distler, Abbot S. Gaunt, John L. Lenz, Gary L. +Packard, A. Wayne Wiens, and John Wellman assisted in various phases +of the field work. + + + + +METHODS OF STUDY + + +Daily observations were made from May 11 to June 26 in 1959 and from +April 15 through July 15 in 1960. Six additional visits were made to +the study area in September of 1959, and ten others in July and +August, 1960. Periods of from one hour to eleven hours were spent in +the field each day, and a total of about five hundred hours were +logged in the field. + +Each territory was visited for at least five minutes each day but more +often for twenty minutes. The breeding activities of the pairs were +rarely synchronous. Consequently several stages in the cycle of +building were simultaneously available for study. + +Nine young and one adult were banded in 1959. No Bell Vireos were +banded in 1960. Individual pairs could be recognized because of their +exclusive use of certain segments of the study area and by the +individual variation in the song of the males. Sexes were +distinguishable on the basis of differences in vocalizations and +plumages. + +Most nests were located by the observer searching, watching a pair +engaged in building, or following a singing male until the increased +tempo of his song indicated proximity to a nest. As the season +progressed and the foliage grew more dense, it became increasingly +difficult to locate completed nests. Blinds were unnecessary because +of the density of vegetation. Observations were facilitated by a 7 x +50 binocular. Data were recorded on the spot in a field notebook. Eggs +were numbered by means of Higgins Engrossing ink as they were laid. + +Individual trees in which males sang most were marked over a +three-week period. Then the distances between the most remote perches +were paced. These distances aided in determining the size of the +territories. The general configuration of the vegetation within each +territory determined the location of one or more boundaries of the +territory. Each territory was given a number, 1, 2, 3, etc., as it was +discovered; consequently there is no numerical relationship between +the designations of the territories established in 1959 and 1960. +Nests within a territory were designated as 1-a, 1-b, 1-c, etc. + +Although experimentation was not a primary source of data, it proved +useful in certain instances. A stuffed Blue Jay elicited mobbing +behavior from nesting pairs. A dummy Bell Vireo elicited both +agonistic and epigamic behavior from nesting pairs, depending on the +phase of the nesting cycle. + +The temperature at the beginning of each day's work was taken by means +of a Weston dial thermometer. A hand counter and a pocket watch having +a second hand were used in determining such data as frequency of song +and periods of attentiveness by the sexes. Histological +cross-sections, prepared by A. Wayne Wiens, of the ventral epidermis +of both sexes were used to study brood patches. + + + + +STUDY AREA + + +The intensive field work was on a 39-acre tract (fig. 1) extending +approximately 7/10 of a mile west from U. S. highway 59, which in +1959-1960 constituted the western city limit of Lawrence, Douglas +County, Kansas. The eastern boundary of the study area is +approximately 1-1/2 miles southwest of the County Courthouse in +Lawrence. The eastern ten acres is associated with the Laboratory of +Aquatic Biology of the University of Kansas. The 15 acres adjacent to +this on the southwest is owned by the University of Kansas Endowment +Association, but is used by Mr. E. H. Chamney for the grazing of +cattle. This portion is bounded on the west by a stone fence, beyond +which lies a 14-acre field of natural prairie owned by Dr. C. D. Clark +that is bordered on the extreme west by a narrow thicket of elm +saplings. + +The principal topographic feature of the area is an arm of Mount +Oread, that rises some 80 feet above the surrounding countryside. +About 200 feet from the crest of the southwestern slope of the hill a +40-foot-wide diversion terrace directs run-off toward the two-acre +reservoir that is the source of water for eight experimental fish +ponds of the laboratory. + +The predominant shrub-vegetation consists of Osage orange (_Maclura +pomifera_), honey locust (_Gleditsia triacanthos_), and American elm +(_Ulmus americana_). These saplings, ranging in height from 3 to 25 +feet, grow in dense thickets as well as singly and in clumps of twos +and threes. Larger trees of these same species grow along the crest of +the hill, along the eastern and southeastern boundaries of the area, +and along the stone fence separating University land from that owned +by Dr. Clark. A dense growth of coralberry (_Symphoricarpos +orbiculatus_) forms the understory just below the crest of the hill. +Isolated clumps of dogwood (_Cornus drummondi_) and hawthorn +(_Crataegus mollis_) are scattered throughout the area. These species +of shrubs grow densely along the stone fence. The isolated thicket on +the Clark land is composed primarily of elm and boxelder (_Acer +negundo_), but includes scattered clumps of dogwood, Osage orange, and +honey locust. Poplars (_Populus deltoides_) are the only large trees +in this area. + + [Illustration: FIG. 1. Map of the study area near the + University of Kansas Laboratory of Aquatic Biology. The dashed + lines mark the approximate territorial boundaries of the + original nine pairs of Bell Vireos from May 1960 to early June + 1960.] + +The open areas between the thickets are grown up in red top (_Triodia +flava_), bluestem (_Andropogon scoparius_), Switchgrass (_Panicum +virgatum_), Kentucky bluegrass (_Poa pratensis_), bush clover +(_Lespedeza capitata_) and mullen (_Verbascum thapsus_). Shrubby +vegetation occupies about 65 per cent of the total area, but in the +Clark portion constitutes only about 35 per cent of the ground cover. + + +_Considerations of Habitat_ + +Nolan (1960:226), summarizing the available information on habitat +preferences of the Bell Vireo, indicates that this species tolerates +"a rather wide range of differences in cover." He pointed out that a +significant factor in habitat selection by this species may be +avoidance of the White-eyed Vireo (_V. griseus_) where the two species +are sympatric. + +In Douglas County where the Bell Vireo is the common species, the +White-eyed Vireo reaches the western extent of its known breeding +range in Kansas. At the Natural History Reservation of the University +of Kansas, where both species breed, the Bell Vireo occurs in "brush +thickets in open places" (Fitch, 1958:270) and the White-eyed Vireo +occupies "brush thickets, scrubby woodland and woodland edge" (Fitch, +_op. cit._, 268). Along the Missouri River in extreme northeastern +Kansas, Linsdale (1928:588-589) found the White-eyed Vireo "at the +edge of the timber on the bluff, and in small clearings in the +timber," while "the Bell Vireo was characteristic of the growths of +willow thickets on newly formed sand bars." Elsewhere in northeastern +Kansas I have found the Bell Vireo in shrubbery of varying density and +often in habitat indistinguishable from that occupied by White-eyed +Vireos at the Natural History Reservation. In the periphery of the +region of sympatry the rarer species is confronted with a much higher +population density of the common species and consequently might well +be limited primarily to habitat less suitable for the common species. +This would seem to be the case in eastern Kansas, presuming that +interspecific competition exists. + +The Bell Vireo has followed the prairie peninsula into Indiana, aided +by the development of land for agriculture. In nearby Kentucky where +thousands of miles of forest edge are found, and where little brushy +habitat of the type preferred by the Bell Vireo occurs, the White-eyed +Vireo is abundant whereas the Bell Vireo is unknown as a breeding bird +(R. M. Mengel, personal communication). + +In more central portions of the area of sympatry, nevertheless, the +two species do occur within the same habitat (Ridgway, 1889:191; Bent, +1950:254) and occasionally within the same thicket (Ridgway, in +Pitelka and Koestner, 1942:105); their morphological and behavioral +differences, although slight, probably minimize interspecific +conflict. The Bell Vireo and the Black-capped Vireo (_V. +atricapillus_) have been found nesting in the same tree in Oklahoma by +Bunker (1910:72); the nest of the black-cap was situated centrally and +that of the Bell Vireo peripherally in the tree. Bell Vireos +invariably place their nests in the outer portions of trees and +peripherally in thickets. This placement would further obviate +interspecific conflict with the white-eye since its nests are placed +centrally in the denser portions of a thicket. + +A critical feature of the habitat preferred by the Bell Vireo is the +presence of water. In far western Kansas this species is restricted to +riparian growth along the more permanent waterways. This in itself is +not adequate proof of the significance of water supply because thicket +growth in that part of the state is found only along waterways. The 20 +areas over the state that I have visited where Bell Vireos were +present were closely associated with at least a semi-permanent source +of water. Fifteen other areas indistinguishable from the 20 just +mentioned, but lacking a permanent supply of water, also lacked Bell +Vireos. Nevertheless areas in which Bell Vireos typically nest are +decidedly less mesic than those frequented by White-eyed Vireos. + +Once the Bell Vireo was probably more local in its distribution being +restricted to thickets associated with permanent water. Clearing of +woodland for agricultural and other use, and subsequent encroachment +of second growth concomitant with the creation of man-made lakes and +ponds, has greatly increased the available habitat for this bird. The +preferred species of shrubs for nesting are reported (Bent, 1950:254) +to be various wild plums (_Prunus sp._). The widespread distribution +and abundance of the exotic Osage orange has greatly augmented the +supply of trees suitable for nesting. + + + + +SEASONAL MOVEMENT + + +_Arrival in Spring_ + +The subspecies of the Bell Vireo breeding in Kansas, _V. b. bellii_, +winters regularly from Guerrero and the Isthmus of Tehuantepec south +to Guatemala, El Salvador, and northern Nicaragua (A. O. U. +Check-list, Fifth Edition, 1957:469-470). In the United States +migrating birds are first recorded in early March (Cooke, 1909:119). +The Bell Vireo is a relatively slow migrator, moving primarily at +night and covering little more than 20 miles at a time (Cooke, _op. +cit._ 119). The average date of arrival, based on 27 records, for +northeastern Kansas is May 8; the earliest record is April 22, 1925, +from Manhattan, Riley County, Kansas (fig. 2-A). + +In 1959 the first bird arrived at the study tract about May 5. No +additional birds were heard singing until the third week of the month, +in which eight new males were noted. As mentioned, in 1960 field work +was begun in mid-April and the study area was traversed daily. No +birds were detected until late afternoon of May 3, when one, +presumably a male, was seen foraging. + +Lawrence (1953:50) has reported that males of the Red-eyed Vireo +precede females in the breeding area by as much as two weeks; the male +Red-eyed Vireo forages but sings little in the pre-nesting period. The +male Bell Vireo arrives first at the breeding area but precedes the +female by only a few days. On the morning of May 4 the first male was +singing from a number of perches while ranging over an area of seven +acres. This area encompassed territories later occupied by three +pairs, 2 (1960), 4 (1960), and 5 (1960). Late on the afternoon of May +4 the first courtship songs were heard and the first male was seen +with a mate at 6:20 p.m. Eight additional males arrived from May 6 +through May 18. A tenth male was discovered in the vicinity of +territory 9 (1960) on June 18, 1960. + + [Illustration: FIG. 2. Seasonal movement as indicated by the + curve for spring arrival (A), based on the earliest dates for + 27 years, and the curve for autumn departure (B), based on the + latest dates for 21 years in northeastern Kansas.] + + +_Fall Departure_ + +The average date of departure for 21 years in northeastern Kansas is +September 3 (fig. 2-B). The earliest date is August 14 from Concordia, +Cloud County, Kansas (Porter, unpublished field notes). The latest +date is September 27 (Bent, 1950:262) from Onaga, Pottawatomie County, +Kansas. In 1959 the last vireo was seen at the study tract on +September 14. The birds do not all depart at the same time. On +September 1 there were still five singing males in the study area; by +September 10 there were three and on September 13, only one. + + + + +GENERAL BEHAVIOR + + +_Flight_ + +In "straight-away" flight the Bell Vireo undulates slightly. In a +typical flight several rapid, but shallow, wing beats precede a +fixed-wing glide of from 1 to 15 feet in length. Because the wings are +extended horizontally during the glide, the bird does not move +distinctly above or below the plane of flight. The White-eyed Vireo +generally appears to be slower and more lethargic in flight than the +Bell Vireo. In the breeding season most flights of the Bell Vireo are +no longer than a few feet between adjacent shrubs and trees, but +occasional sustained flights are as long as 300 feet. The birds fly as +low as 2 feet above ground, but have often been observed as high as 70 +feet above the ground. + +In courtship and protracted territorial disputes, where chase between +sexual partners or a pair of antagonists occurs, looping flights are +observed. The wings are beaten as the birds climb and many aerial +maneuvers are performed in the course of the glide. + + +_Foraging and Food Habits_ + +The Bell Vireo has been characterized as a thicket forager (Hamilton, +1958:311; Pitelka and Koestner, 1942:104), but in my experience it is +not restricted to low level strata; birds forage from ground level +upward, both in thickets and isolated trees ranging in height from 3 +feet to 65 feet. The tendency to forage at higher levels is in part +dictated by the presence of tall trees within the various territories. + +Territories 1 through 7 (1960) contained from three to ten trees +surpassing 40 feet in height. They grew singly or in small groves. The +Bell Vireos foraged fully 20 per cent of the time in these trees. Food +was sought throughout the leaf canopy. + +Behavior in foraging in larger trees followed a routine pattern. +Typically a pair alighted in a tree at a height of 15 feet. Then the +female hopped to a perch a foot above the one upon which she landed. +The male succeeded her to the perch she had previously occupied. The +pair in effect spiraled around some large, essentially upright, +branch, in foraging. The birds usually reached higher perches in this +manner rather than by flying upward 10 to 15 feet to them. This manner +of progression within a tree is reminiscent of a similar habit of the +_Cyanocitta_ jays. Presumably, the habit of the Bell Vireo of foraging +in higher strata is facilitated by the absence of other species of +arboreal foraging vireos. + +Chapin (1925:25) found the Bell Vireo to be more insectivorous in its +food habits than any other North American vireo. He found 99.3 per +cent of all food contained in 52 stomachs to be of animal origin. Only +three times have I seen a Bell Vireo take food of vegetable origin. On +September 9, 10, and 14, 1959, I noted a male eating wild cherries +over a period of 65 minutes of observation. Chapin (1925:27) noted +that beginning in July vegetable matter represented 1.57 per cent of +the bird's subsistence, and thereafter slightly more until fall +migration. + +Animal food, consisting primarily of insects and spiders, is actively +sought along branches and under leaves. Often a foraging bird will +leap to the underside of a branch and hover, mothlike, beneath a +cluster of leaves while extracting some insect. Some individuals hung +upside down on small branches, paridlike, while foraging. Lawrence +(1953:710), and Southern (1958:201) have recorded similar behavior of +the Red-eyed Vireo. Occasionally, I have seen a Bell Vireo fly from a +perch and capture an insect in the manner of a flycatcher. The birds +do not appear to be adept at this type of food-getting. Nolan +(1960:242) mentions Bell Vireos holding hard-bodied insects by means +of their feet while breaking the exoskeleton with the beak to obtain +the soft parts. Southern (1958:201) recorded a female Red-eyed Vireo +foraging on the ground; I have seen a Bell Vireo on the ground but +once, and it was gathering nesting material. + + +_Bathing_ + +On May 14, 1960, in a rill that empties into the northeastern edge of +the reservoir a female flew down from a perch six inches above the +surface, barely dipped into the water, flew to a perch 12 inches above +the water, violently shook her ruffled body feathers, quivered her +wings, and rapidly flicked her fanned tail. The entire procedure was +repeated three times in five minutes. She was accompanied by a singing +male that did not bathe. + +Nolan (1960:241) reports a male Bell Vireo bathing by rubbing against +leaves wet with dew; he notes that the White-eyed Vireo bathes in a +similar manner. Southern (1958:201) twice observed Red-eyed Vireos +bathing in water that dropped from wet leaves. In my study area in +1960, only territories 7, 8, 9, and 10 were not immediately adjacent +to permanent water. The pairs of Bell Vireos in those territories +presumably had to reply on wet vegetation for bathing. + + + + +VOCALIZATIONS + + +The male Bell Vireo begins to sing regularly soon after its arrival in +spring. Some daily singing continues following the cessation of +breeding activities until departure of the species in late summer or +early fall. The highest sustained rate of song occurs on the first and +second days of nest building. Because careful records of +meteorological data were not kept, I cannot significantly correlate +rates of song and specific temperatures and other weather conditions. +Frequency of song was reduced when the temperature rose above 90° F., +as it did on many days in June, 1960. Nice (1929:17) mentions a +similar decrease in singing when the temperature exceeded 85° F. + +Passerine birds typically sing at a high rate throughout courtship and +nestbuilding, but at a markedly lower rate thereafter. Most vireos are +atypical in this respect. In the study area in 1960 Bell Vireos sang +more often than Robins, Mockingbirds, Field Sparrows, Brown Thrashers, +Catbirds, and Doves breeding in the same habitat, about as often as +the Meadow Larks in the adjacent fields, and less often than Painted +Buntings. + +The Bell Vireo seems to sing less often in the undisturbed state than +when aware of the presence of an observer. Observations from my car, +at a site approximately equidistant from territories 1 (1960), 2 +(1960), 4 (1960), and 6 (1960) indicate that the rate of song during +incubation is decidedly less when no disturbing influence is present. +Normally, in this period, song aids in maintaining contact between the +members of a pair, serving to locate the male as he forages. Mumford +(1952:230) noted that the males often came out to meet him as he +entered their territories, singing as they approached. The male +typically continues to sing for some time after the intruder has +departed. Here the song acquires the additional functions of alerting +the female to danger and threatening the trespasser. Even after +allowance is made for this reaction to disturbance, Bell Vireos sing +more often than most of their nesting associates, and, on a seasonal +basis, they are vocal for a much longer time. + + +_Singing Postures_ + +In the normal singing posture the body of the Bell Vireo is maintained +at an angle of 35° to the horizontal. Occasionally, during nest +building, I have observed the body held at angles as severe as 80° +from the horizontal. + +The head of the White-eyed Vireo is distinctly bobbed up and down, two +or three times, during the utterance of a song phrase. A bob involves +a deliberate withdrawal of the head towards the body and subsequent +sharp, almost vertical, extension of the neck. The head of the Bell +Vireo does not bob, although it vibrates as the song is delivered. + + +_Flight Song_ + +The Bell Vireo does not have a distinctive flight song; in fact, it +rarely sings or calls while in flight. Nolan (1960:240) has recorded a +male singing the normal song while in flight. Sharp scold-notes are +uttered in mid-air when a bird is agitated or actually attacking an +enemy. These notes and songs recorded by Nolan hardly qualify as +flight song, for this term implies use of a distinctive vocalization +not uttered in other circumstances. + + +_Daily Frequency of Song_ + +In the morning, Bell Vireos usually began singing a few minutes before +sunrise. Their songs were invariably preceded in the study area by +those of Western Kingbirds, Robins, Mourning Doves, Mockingbirds, +Cardinals and Meadow Larks. Bell Vireos sang relatively little after +6:30 p.m., even on the longest days of the year. The latest daytime +singing that was recorded was seven songs at 7:18 p.m. on June 20, +1960. A Cardinal in the vicinity sang for a full hour after this. + + +_Types of Vocalizations_ + +Six vocalizations were readily distinguishable in the field. These are +divisible into songs and call notes. + +1. Primary song. It has been described by Pitelka and Koestner +(1942:103) as an "irregular series of harsh and sharp, but slurred +notes preceded by a few distinct notes of the same quality and ending +with a decided ascending or descending note of similar harshness." The +terminal note may also be somewhat abbreviated and intermediate +between an ascending or descending note. The song is sometimes +delivered as a couplet that consists of a phrase ending on a +descending note. This delivery is typical of incubation and later +renesting. During early season activities, the bird utters a phrase +ending on the descending note as many as 15 times before a phrase +ending on an ascending note is heard. + +A sonagram of a single phrase, one of several recorded on May 9, 1960 +(the third day of building of nest 1-b 1960), consists of 10 notes, +the first of which is distinct. The remaining notes are slurred. This +phrase is 1.4 seconds in length. + +Songs are delivered most rapidly in the course of territorial disputes +and defense. The song is loudest in times of nestbuilding and periods +of aggressive behavior. At these times, on clear, calm days, the songs +are audible 100 yards away. Singing in the nestling period and +post-breeding season is audible at distances of no more than 50 feet; +such notes have been termed "whisper songs." Table 1 summarizes +singing rates at different periods of the nesting cycle in several +situations and under various weather conditions. + +Songs are of equal frequency in the immediate vicinity of the nest and +elsewhere in the territory. Nice (1929:17) also found this to be true. +Perches can be almost at ground level or as high as 60 feet. Forty per +cent of my data on song concern singing at heights of more than 20 +feet. As indicated in foraging, the lack of competition from aboreal +species of vireos presumably contributes to the use of higher perches +by Bell Vireos. + +No female song was recorded in 1959, but on May 26, 1960, a female was +heard to sing once. She appeared at nest 1-f (1960) shortly after the +male arrived. Unlike him, she did not participate in building, but +seemed to be inspecting the nest. After 30 seconds she sang once--a +low garbled phrase--and also scolded once. After this she left. In the +meantime the continuously singing male moved two feet away from the +nest, then back to it and resumed construction. + +The song of the female signaled to the male her departure. Pitelka and +Koestner (1942:103) heard a female sing twice after she replaced the +male on the nest. Females of three other species of vireos, the +Black-capped Vireo, _V. atricapillus_ (Lloyd, 1887:295), the +Philadelphia Vireo, _V. philadelphicus_ (Lewis, 1921:33), and the +Latimer Vireo, _V. latimeri_ (Spaulding _in_ Pitelka and Koestner, +1942:103) have been heard singing. Lewis and Spaulding also suggest +that the song of the female functions as a signal prior to exchange at +the nest. + +The primary song identifies the singer as a male Bell Vireo. It +aids in securing a mate and in warning potential adversaries; also, +the song is a signal in certain situations and serves to locate the male. + + TABLE 1. REPRESENTATIVE SINGING RATES OF BREEDING BELL VIREOS. + ALL RATES WERE AT AIR TEMPERATURES LESS THAN 86° F. EACH + INSTANCE REPRESENTS APPROXIMATELY 30 MINUTES OF OBSERVATION. + + ==================================================================== + | | Average + Circumstance | Instances | rate per + | | minute + ----------------------------------------------+-----------+--------- + Attraction of mate | 2 | 6.3 + Territorial dispute | 5 | 12.8 + Nestbuilding | 6 | 7.0 + Egglaying | 1 | 3.0 + Incubation | 6 | 3.9 + Exchange of partners in the incubation period | 1 | 4.0[A] + Foraging | 2 | 2.2 + "Morning" song | 1 | 28.6[A] + "Evening" song | 1 | 1.9[A] + ----------------------------------------------+-----------+--------- + Over-all average rate per minute 6.3 + + [A] Not sustained; data representative of periods less than 5 + minutes in length. + +2. Courtship song. It is here termed the "congested" song and is +comparable to the adult "run-on" song mentioned by Nolan (1960:240). +The congested song is a squeaky version of the primary song and is +given when birds are engaged in pair-formation, nestbuilding, and +egglaying. The delivery is rapid and the sound can be likened to that +made by rapidly scraping a bow across a taut violin string. Nolan +(_in_ Mumford, 1952:230) is probably speaking of this song when he +describes a "tuneless" song that "had a jerky, sputtering quality that +characterizes part of the song of the Ruby-crowned Kinglet (_Regulus +calendula_)." More recently (1960:240) he applies the adjectives +"twanging," "Bobolink-like," "bubbling," "jerky," and "squeaky." This +song is often blended with the primary song and is audible for 75 +feet. + +A specialized version of the congested song is associated with +pre-and post-copulatory display but differs from the typical squeaky +performance in terminating in two ascending notes reminiscent of the +ascending phrase of the primary song. + +3. Distress call. It was heard only once, when a captured bird was +being freed from a net. When the bird was almost disentangled it +uttered 10 high-pitched, plaintive notes. The quality of the notes +suggested a relationship to the song phrase rather than to other types +of vocalization. A nesting pair of Bell Vireos, 10 feet away, became +extremely excited when they heard the distress notes. They "scolded" +vigorously and flew around my head at a distance of six feet. + +4. Alarm note. This is a specialized, three-note call of the male and +was heard only from the onset of pair-formation through early +nestbuilding. This whinnying, flickerlike call, phonetically +_eh-eH-EH_, each succeeding note of which is louder than the one +before, is given whenever the male is disturbed by an unfamiliar +object. This call is generally succeeded by the _chee_, but +occasionally blends into an extended "whinny," and is typically given +from some perch affording an unobstructed view of the offending +object. The male stretches his neck and cocks his head, the wings and +tail are not flicked or fanned, and no feather tracts are erected. The +bird, nevertheless, flits nervously from perch to perch when uttering +the call. + +5. The _zip_. The male has a special "scold" note of his own that is +heard when an intruder first approaches the nest. Phonetically it is +_zip-zip-zip_. It is not so loud as the _chee_, and the delivery is +more deliberate than that note. If the intruder remains near the nest, +the _zip_ is usually replaced by the _chee_. + +6. The generalized call note or _chee_. The call notes associated with +several situations are combined under this subheading since all can be +rendered in English by the same phonetic equivalent--_chee_. The +_chee_ associated with nestbuilding is of moderate pitch and delivered +deliberately at a rate of about 40 per minute. The feeding call of the +adults is a soft slurred _chee_, while that of the nestlings has a +mewing quality. In general, the _chee_ utilized in signal situations +consists of a few repetitions of the basic note emitted at a moderate +pitch. The _chee_ associated with hostile and courtship behavior is +higher pitched and the delivery is much more rapid, approximately 200 +per minute. Nolan (1960:240) reports a continuous rate of 25 per five +seconds when an adult Bell Vireo is alarmed. The _chee_ of extreme +anxiety is a loud emphatic buzz, phonetically ZZ-ZZ-ZZ-ZZ. + + + + +TERRITORIALITY + + +The Bell Vireo exhibits "classic" passerine territoriality. Within a +specific area, a pair of this species carries out pair-formation, +courtship activities, copulation, nesting, rearing the young, and +foraging. With the cessation of reproductive activities, a pair +continues to restrict its other daily activities to the same general +area. + + +_Establishment of Territory_ + +In early May the segment of the total suitable habitat within which a +Bell Vireo restricts its activities is not rigidly defined and the +first male of the season ranges over an area too large to be +maintained permanently--one that seems greatly to exceed the needs of +breeding. Male 1 (1960), for instance, was first seen foraging over an +area of approximately seven acres. With the influx of other males, +portions of this large tract were usurped and the territory of the +original male was gradually reduced to an area of little more than an +acre. + +In this initial period, a male becomes identified with a large area +but is restricted to an area of nearly typical size by the +encroachment of other males. Territorial disputes in this period often +involve physical contact, as well as protracted sessions of +high-intensity singing at rates exceeding three hundred song-phrases +per hour. + +Eventually the carrying capacity of the habitat is reached and no +further partitioning occurs. The beginning of nestbuilding coincides +with this relative stabilization of the territorial boundaries. +Through the remainder of the cycle of behavior associated with any one +nest, all activity is that of the occupant pair within its territory. + + +_Size of Territories_ + +The nine original territories established in 1960 varied in size from +0.26 acre to 3.1 acres (Table 2). Fitch (1958:270) found the +territories of several pairs of Bell Vireos at the University of +Kansas Natural History Reservation to vary from 0.4 to 1 acre. Hensley +(1950:243) estimated the size of the territory of a pair of Bell +Vireos observed in Piatt County, Illinois, at 3.1 acres. Nolan +(1960:227) records home ranges of 2 to 3 acres. The pairs that he +studied were sole occupants of fields several acres larger than the +portions actually utilized. His description of the vegetation +indicates that most of the second growth was not much taller than 7 +feet. As indicated elsewhere, the second-growth in my tract averaged +15 feet tall. The smaller average size of territory (1.25 acres) that +I found is probably a function both of this greater vertical range of +available foraging area and the much higher gross density of birds (40 +pairs per 100 acres). + + +_Permanence of Territories_ + +Most pairs remain in their original territories throughout the summer, +although some shift certain territorial boundaries. In 1960 pairs 2 +and 6, in the course of selecting a site for a replacement nest, +annexed adjacent areas previously occupied by other pairs. Pair 2 +relocated in a space that originally included territories 1 and 4, and +pair 6 built a nest in an area formerly occupied by pair 7. Males 1 +and 4 were sacrificed for specimens and pair 7 probably was destroyed +by a predator. Owing to the presence of a nest, the annexed area +becomes the focal point of the activities of a pair, but the original +area is regularly visited and may be returned to in a later renesting. + + TABLE 2. SIZE OF THE NINE ORIGINAL TERRITORIES OCCUPIED IN 1960. + + ========================================== + | Date first | + Territory | occupied | Dimensions + -------------+--------------+------------- + 1. | May 3, 1960 | 1.6 acres + 2. | May 5, 1960 | 0.6 acre + 3. | May 7, 1960 | 0.26 acre + 4. | May 11, 1960 | 1.03 acres + 5. | May 12, 1960 | 2.07 acres + 6. | May 14, 1960 | 3.1 acres + 7. | May 13, 1960 | 1.7 acres + 8. | May 14, 1960 | 0.46 acre + 9. | May 14, 1960 | 0.4 acre + -------------+--------------+------------- + Average 1.25 acres + + +_Maintenance of Territory_ + +Except in the early stages of nesting, territory is maintained +primarily by song. In the period of incubation a male regularly +patrols his territory between sessions of sitting on the eggs. He +sings several songs from each of several perches. A male follows a +predictable path, rarely traveling more than 150 feet from the nest. +Incipient patrolling is seen early in the breeding season when +territorial boundaries are in a state of flux. + +The male White-eyed Vireo travels a semi-predictable route, as does +the Solitary Vireo (R. F. Johnston, MS). According to Lawrence +(1953:50), the male Red-eyed Vireo has a distinct singing area +completely divorced from the nest area dominated by the female. +Southern (1958:109), working with this same species in Michigan, did +not recognize separate areas, but found that the male wandered +randomly over the territory. + +In a species so highly active as the Bell Vireo, the degrees of +hostile action associated with an encounter overlap in such a fashion +that no clearcut distinction can be drawn among the various displays. +Nevertheless, certain generalized patterns are characteristic of all +situations in which members of this species are in a state of anxiety. +The threat displays described in the succeeding paragraphs may all be +utilized within as little as two minutes; mutual agonism may be +terminated at any stage by concerted attack of the dominant bird. + +1. Vocal threat. When an intruder is discovered the resident male +markedly increases his rate of singing. The alarm note, _eh-eH-EH_, is +the first call uttered during the nestbuilding and egglaying periods. + +2. Head-forward threat. If the intruder does not flee, the resident +male adopts a specific threat posture. The head and neck are extended. +The feathers of the crown are erected, but those of the body are +sleeked. The bird crouches slightly and the tail is flicked laterally, +but not fanned. The intensity of the singing increases and is +supplemented by scolding, also delivered at a rapid rate. The intruder +normally retreats at this juncture. + +3. Wing-flicking and submaximal tail-fanning. If the interloper +remains, the anxiety of the resident male increases. He slightly +depresses the tail and, at the same time, rapidly fans and closes it. +The tail is only partially fanned. The wings are held slightly away +from the body and rapidly flicked above the back. This flicking should +not be confused with quivering of the wings associated with begging +and other solicitory postures. Song is now almost completely replaced +by high-intensity scolding. Associated with this high degree of +anxiety are displacement behaviorisms, including bill-wiping, reversal +of direction on a single perch, and a nervous hopping from one perch +to another. + +4. Ruffling and maximum tail-fanning. This display is most often seen +in conjunction with the harassment of predators, but occasionally it +is observed in territorial disputes occurring at the boundary of +adjacent territories where neither male is strictly dominant and in +which there is much vacillation prior to attack. The feathers of the +abdomen are ruffled. The term "ruffled" pertains to a full erection of +the feathers, giving a ragged appearance to the body outline (Morris, +1956:80). Ruffling of the abdominal feathers emphasizes their yellow +color and seemingly heightens the intimidatory effect. The tail is +fully fanned, and so maintained, for a few seconds at a time; it is +held at a 45° angle to the body. The scold becomes an extremely +intense, stacatto buzz, ZZ-ZZ-ZZ-ZZ. + +5. Supplanting attack. The attack directed against a trespassing male +is initiated as a lunge that results in a collision with the opponent +in mid-air or on his perch. The bird attacked is struck by his +adversary's open beak or body. + +Hinde (1952:71-72) indicates four courses of action followed by a +Great Tit (_Parus major_) when attacked under similar circumstances. +"(a) It flies away: The attacker usually flies after it and a chase +ensues. (b) It shifts its perch a few inches: the attacker lands in +its place, and both usually show head-up postures. (c) It remains +where it is, but adopts a head-up posture: the attacker usually then +shows upright flight. (d) It may fly up and meet the attacker in +mid-air: in that case an actual combat may result, or both combatants +may show upright flight." + +Head-up posturing and upright flight are not presently recognized +components of the behavior of the Bell Vireo. The behavior of the +attacked Bell Vireo is similar to that described in (a), (b), and (d) +above, and is clearly dictated by the proximity of his own "home +base." + +Eleven disputes among occupants of adjacent territories were witnessed +between May 6 and June 3, 1960, in which some or all of the described +threat displays were manifest (Table 3). In each instance, patrolling +males were gradually attracted to each other. As they approached, +their rates of song increased from an average of six repetitions per +minute to 15 per minute. Eight of the disputes involved physical +combat. + +On May 6, 1960, when male 2 (1960) was in the process of usurping an +eastern segment of the original territory of male 1 (1960), a violent, +protracted dispute was observed. By this date male 1 (1960) had +obtained a mate and had begun construction of nest 1-a (1960); male 2 +(1960) had not yet acquired a mate. At first the two males were +singing vigorously, from one to 10 feet apart. Female 1 (1960) +followed her mate closely and scolded, at the same time partially +fanning her tail. In the course of vocal dueling the males had +traveled to within 50 feet of nest 1-a (1960), when male 1 (1960) +suddenly lunged at 2 (1960). The males plunged to the ground, locking +bills and clutching at each other with their feet as they fell. As +soon as they touched the ground they separated. Male 2 flew east with +male 1 in pursuit. This conflict lasted three minutes. + +Additional physical combat was witnessed several minutes later. This +again involved striking with the bill, wings and feet. A high pitched +squeaky _chee_ was uttered by both combatants. The female scolded from +a nearby perch. Upon separating, the males engaged in a wild, looping +flight. At about 350 feet from nest 1-a (1960), the chase abruptly +ended. For ten minutes thereafter, both males sang at a high rate from +perches about 10 feet apart. This terminated the physical combat, but +three additional protracted, vocal duels occurred in the remainder of +the morning. + + TABLE 3. INTRASPECIFIC DISPUTES IN MAINTENANCE OF TERRITORY. + + Behavior + + ============================================================== + | Number | | | Average + | of | Vocal | | length of + | conflicts | dueling | Combat | disputes + -------------+-----------+---------+--------+----------------- + Prenesting | 3 | 3 | 2 | 6 min. 40 sec. + Building | 8 | 8 | 6 | 3 min. 8 sec. + Incubation | 1[B] | 1 | ... | 20 min. + +-----------+---------+--------+----------------- + Totals | 12 | 12 | 8 | 5 min. 30 sec. + -------------+-----------+---------+--------+----------------- + + [B] Directed against a stuffed Bell Vireo. + +Probably as a direct result of these conflicts, a neutral zone +approximately 300 feet wide developed between the two territories. By +May 14 this intervening area was occupied by male 4 (1960). By this +date both 1 (1960) and 2 (1960) were involved in nestbuilding and 4 +(1960) was not challenged for several days. + +Maximum tail-fanning prior to attack also appears as an element of +aggressive behavior in White-eyed Vireos. A brief skirmish between a +male of this species and a small, greenish passerine was observed at +the Natural History Reservation on May 25, 1960. The White-eyed Vireo +was singing from a perch 30 feet high in a dead elm, when the +unidentified passerine landed 10 feet distant. The white-eye ceased +regular song and uttered several catbirdlike calls, and at the same +time slightly depressed and fully fanned the tail. After 10 seconds, +the white-eye lunged at the intruder, striking it in mid-air. A brief +looping flight ensued through the branches of the elm before the +intruder was able effectively to retreat. + + +_Aggressive Behavior of the Female_ + +The female Bell Vireo is concerned primarily with the defense of the +nest and the young and she rarely assists the male in defense of +distant parts of the territory. She employs the same threat displays +as the male. + + +_Interspecific Relationships_ + +A number of meetings between Bell Vireos and other species were +observed in the course of the study (Table 4). Resident pairs of this +species exhibited different degrees of tolerance toward other species. +Many birds, including Cardinals, Field Sparrows, Painted Buntings and +Mourning Doves were ignored completely. Chickadees evoked responses +characterized by slight increase in song and some anxiety; this was +perhaps owing to similarity in size, motion and call notes. Warblers, +when met with, were invariably chased. They may be momentarily +mistaken for rival vireos. + + TABLE 4. INTERSPECIFIC CONFLICT OBSERVED IN 1959 AND 1960. + + ================================================================== + | Number | Phase of | Behavior of + | | | Bell Vireos + Species | of | breeding +------+---+----+--- + |conflicts| cycle |HFT[C]| S | TF | A + ---------------------+---------+--------------+------+---+----+--- + _Coccyzus | 1 | Nestling | | | | + americanus_ | | period | -- | x | | + | | | | | | + _Cyanocitta | 3[D] | Nestling and | | | | + cristata_ | | incubation | | | | + | | period | x | x | x | x + | | | | | | + _Parus atricapillus_ | 1 | Prenesting | -- | x | | + | | | | | | + _Molothrus ater_ | 1 | Nestling | | | | + | | period | -- | x | -- | x + | | | | | | + _Dendroica petechia_ | 1 | Prenesting | -- | x | -- | x + | | | | | | + _Geothlypis trichas_ | 1 | Nestbuilding | -- | x | -- | x + | | | | | | + _Pituophis | | | | | | + catenifer_[E] | 1 | Post-fledging| -- | x | -- | x + ---------------------+---------+--------------+------+---+----+--- + + [C] HFT = head-forward threat; S = scolding; + TF = tail-fanning; A = attack. + + [D] Includes attack against a dummy Blue Jay. + + [E] The Bull Snake is here included because the vireos + directed typical aggressive displays towards it. + +Blue Jays were vigorously attacked, especially late in incubation and +throughout the nestling period of the Bell Vireo. I did not see a jay +struck, but a vireo would circle one closely as it perched and pursue +it when it flew, following as far as 100 yards beyond territorial +bounds. The buzz, ZZ-ZZ-ZZ-ZZ, was uttered in conjunction with this +harassment. + +A stuffed jay placed eight feet from a nest elicited threat display +and displacement behavior from the owners of the nest, but no attack. +Incubation had just begun at this nest. A dummy Bell Vireo placed +close to another nest only momentarily disturbed the male, and the +female completely ignored it. Incubation had also recently begun at +this nest. At this same general stage, moreover, nesting pairs showed +little inclination to harass me. + + +_Discussion_ + +Hinde (1956:341-342) indicates that territory has been defined in a +number of ways by many workers. All of the definitions involve +modification of Howard's classic "defended area." Pitelka (1959:253) +has reacted against this behaviorally-oriented concept. He thinks that +the concept of territory should be based on exclusive use of an area +by its occupants, and not so much the defense by which they maintain +it. + +Methods of treating territoriality in the Bell Vireo seemingly +incorporate features of both schools of thought. The area used +exclusively for all biological needs by a single pair of Bell Vireos +is vigorously defended both physically and vocally early in the +breeding season and vocally as the season progresses. + +In the period of territorial establishment a relatively large area is +actively defended. The building of a nest establishes a focal point of +activity in a somewhat more restricted area than that originally +occupied. After the success or failure of a nest, a new site is +selected to which the focal point of activity is shifted. If suitable +habitat adjacent to the extant territory is unoccupied by other Bell +Vireos the unoccupied area may be annexed in the course of searching +for a new site. Such annexation occurs only when pairs formerly +occupying adjacent suitable habitat disappear from this territory; +possibly the size of the territory of any one pair is dictated by the +density of population of the species as well as by the presence of +suitable habitat. This may not always be true as indicated by Kliujver +(1951:40), who in studying the Great Tit, found no appreciable +difference in the size of territory in two different habitats even +though there was a marked difference in population density of the +birds. + +Fluctuation of territorial boundaries is not uncommon in passerines, +especially when no rivals exist to contest movement. Hinde (1956:351) +indicates that fluctuations in size of territory are to be expected +although the territories of different species of birds have different +mean sizes. + +Once nesting activities commence there is a marked reduction in the +amount of territory utilized and a distinct decrease in the aggressive +tendencies of the male; it would seem that energy previously utilized +in regular fighting is rechanneled for nestbuilding, incubation and +care of the young. Further, contraction of the area of activity +obviates high-intensity territorial defense, as adjacent males, even +in regions of high population density, are isolated from one another +by an area no longer regularly traversed. + +With cessation of breeding activities physiological mechanisms +governing maintenance of territory seemingly are no longer active and +yet the pairs of Bell Vireos remain within a restricted area which +they alone use. Earlier definitions of territory as a "defended area" +do not adequately cover such situations and yet from the standpoint of +Pitelka the area still retains the characteristics of true territory. +In fact, territory as defined by Pitelka is clearly manifest at this +time. Whether the birds remain in an area through "force of habit" is +of little consequence. + +I have retained the term "territory" in preference to the term "home +range" used by Nolan (1960:227). His failure to observe territorial +defense is responsible for his terminology, although it is readily +understandable that such defense would be lacking in a population of +relatively low density in which pairs were isolated from one another +by areas of unfavorable habitat. This isolation in itself would tend +to preclude territorial conflict but territories were, in fact, +maintained. + +The marked similarity in the essential features of aggressive behavior +in North American vireos attests to their close relationship. Flicking +and fanning of the tail are distinct components of the hostile +behavior of the Bell Vireo, White-eyed Vireo, Red-eyed Vireo +(Lawrence, 1953:69), and the Black-whiskered Vireo (_Vireo +altiloquus_; Bent, 1950:319), and, presumably, of the remaining +species of the genus. The occurrence of these same displays as +intrinsic behavioral elements of interspecific hostility suggests a +common derivation. Moynihan (1955:256) indicates that all +intraspecific hostile displays, and probably most interspecific +hostile displays, evolved originally as social signals having the same +general function. Further, Hinde (1956:344) points out that there is a +fundamental similarity in the motor patterns used in fighting in +different contexts, including both interspecific and intraspecific +fighting. + + + + +COURTSHIP BEHAVIOR + + +The precise mechanism of pair-formation in the Bell Vireo is not +known. My experience has been to find a male one day and then one or +two days later to discover that it has a mate. Lawrence (1953:53), +tells of a male Red-eyed Vireo singling out a female from a flock of +migrants passing through his territory and violently driving her to +the ground. Shortly after this attack the pair was seen searching for +a nest site. But such an incident has not been reported for other +vireos, nor have I witnessed such behavior myself. + +Early courtship activities of the Bell Vireo are characteristically +violent affairs, with the male directing strong aggressive attacks +toward the female. Rapid, looping flights through the thickets occur, +the female leading the male. Occasionally he deliberately collides +with her in mid-air, but the pair quickly separate. This violent +sexual chasing is manifest prior to the inception of nestbuilding. +With commencement of this activity, sexual chases through the +territory subside. + +Absence of sexual dimorphism in the Bell Vireo obviously suggests that +behavioral criteria are used by the birds in sex-recognition. The lack +of aggression by the female upon initial aggression by the male is an +essential component of recognition of sex; she is clearly subordinate. +Such subordination is also the significant feature of continued +sex-recognition. Courtship display by a resident male, directed toward +a stuffed male and a wounded male which sat motionless, supports the +contention that a subordinate or submissive attitude of the female is +a key factor in sex-determination. + +Nestbuilding and courtship are intimately associated in this species. +The male constructs the suspension apparatus of the nest, the +completion of which coincides with the assumption of nestbuilding +activity by the female. Roles of the sexes in nestbuilding are +described in the section on nestbuilding. The male frequently +interrupts construction to court the female. This, in combination with +perpetual song as he works, serves to strengthen the pair-bond and +stimulate nestbuilding tendencies of the female. + +It is doubtful that any attempts at copulation are successful up to +this time. The female is singularly unresponsive to the advances of +the male; a female retreats before most violent attacks and is +seemingly oblivious to less vigorous behavior. After the female +assumes the responsibility of building, the tempo of courtship +activities increases. + +The female becomes increasingly more receptive and her work is often +interrupted by advances of the male. Copulation occurs frequently from +about the third day of nestbuilding through the first day of +egglaying, a period of four to six days. Male displays and +vocalizations associated with courtship continue through the fourth or +fifth day of incubation. + + +_Displays and Postures_ + +The principal courtship displays and postures that were seen +throughout the nestbuilding phase are as follows: + +1. Greeting ceremonies. Both birds are crouched from one to five +inches apart. The feathers on one (the male?) are sleeked, and on the +other are fluffed. Fluffing (Morris, 1956:80) denotes partial erection +of the body feathers producing a rounded, unbroken body line and is +not to be confused with ruffling, mentioned in the sections pertaining +to territoriality and pre- and post-copulatory display. Fluffing is +generally considered to be an appeasement display and it is seen in a +variety of situations involving a dominant-subordinate relationship. +Both birds flick wings and tails rapidly and reverse directions on +their perches frequently. A low, rapid _chee_ is uttered during this +performance. This ceremony is repeated often in the first three days +of nestbuilding, but less frequently thereafter. It usually occurs +after building by one or both partners and prior to another trip in +search of nesting material. It lasts from 10 to 50 seconds and is not +immediately followed by any additional courtship activities. Nolan +(1960:228-229) observed mutual displays between periods of violent +sexual chase that suggest that the greeting ceremonies that I have +described are an integral part of pair-formation as well as a +component of continued maintenance of the bond. + +2. "Pouncing." The female rapidly quarter-fans and partially depresses +her tail. She utters a high pitched scold (_chee_). The male, from a +perch within two feet of the female, fans the tail fully and depresses +it vertically, and, with mouth open, lunges at the female; or, with +similar tail mannerisms, the abdominal feathers ruffled, the wings +held horizontally, and the primaries spread, he sways from side to +side from four to six times, and then lunges at the female. The male +is silent when he pounces; the _chee_ or the courtship song is emitted +when swaying precedes pouncing. The male strikes the female with his +breast or with his open beak. The female rarely flees although she is +usually displaced several inches along the branch upon which she is +sitting. However, the female may fly several inches to a new perch. +The failure of the female to adopt a solicitation posture presumably +indicates sexual unreadiness. Instances of the male deliberately +colliding with the female as she flies in the course of gathering +nesting material are probably analogous to pouncing. In none of the +above situations are females observed to fight back in any way. Nice +(1943:174) believed pouncing to be analogous to sexual chasing found +in such species as the Red-winged Blackbird. In the Song Sparrow, +pouncing is observed most often in the first and second days of +nestbuilding. + +3. "Leap-flutter." The male, in the course of displaying with the tail +fanned before the female, suddenly leaps eight inches to ten inches +vertically and flutters in mid-air several seconds, before dropping to +the original perch. This display occurs in full view of the female. It +is often associated with pouncing and is also seen prior to +copulation. In the latter instance it is probably pragmatically +functional, for it permits the male to orient above the female before +dropping to her back to copulate. No vocalization is uttered during +the leap-flutter. + +4. Pre-copulatory display (Fig. 3). The male faces the female. The +tail is fanned fully and depressed at a sharp vertical angle to the +body. Body feathers, both dorsal and ventral, are ruffled, almost +tripling the apparent volume of the thorax. The head is withdrawn and +slightly thrown back. Feathers of the head are not erected. The mouth +is opened wide. The legs are slightly flexed and the body is swayed +laterally. Horizontally, the head and body traverse an arc of about +100°; vertically, they traverse an arc slightly less than 180°. At the +low point of any one swing, the delivery of the courtship song begins. +At the termination of the swing the two normal, ascending notes are +emitted. This performance may last as long as three minutes. + + [Illustration: FIG. 3. A single male Bell Vireo in the + pre-copulatory display. Note the ruffled dorsal and ventral + body feathers. The male on the left has reached the zenith of + a single swing. The male on the right has nearly reached the + low point of a swing.] + +The pre-copulatory display of the male elicits receptive behavior in +the female. She crouches in a solicitous manner, with the body +feathers fluffed and the tail raised slightly, and utters a muted +_chee_. + +5. Copulation. The male abruptly terminates his swaying display with a +leap-flutter that positions him above the female's back. He then +descends and copulation occurs. The male continues to flutter his +wings to maintain balance throughout the two seconds of cloacal +contact. Following an unsuccessful copulation on June 23, 1960, +displacement preening and bill wiping were performed by both sexes. + +6. Post-copulatory display. On June 25, 1960, after a second attempt +at copulation with a stuffed bird in which semen was actually +deposited on the dummy's back, male 10 (1960) performed a swaying +display. In this instance, however, instead of addressing the dummy +from the front, the male alighted one inch to the right of the stuffed +bird. When swaying to the left (toward the dummy) the head of the +displaying male actually passed above the neck of the stuffed bird. +This ritualized behavior could conceivably be derived from +hetero-preening. + + +_Discussion_ + +Within the scope of my research it was difficult to detect the +over-all sequence of epigamic displays that result in synchronization +of the physiological states of the sexes throughout the period of +courtship. Possibly all displays, except the post-copulatory one, +occur in no particular order in the courtship period. However, each +ritualized display seemingly strengthens the pair-bond. + +Swaying has been recorded in a variety of situations of a sexual and +semi-sexual nature for the Solitary Vireo (_V. solitarius_; Townsend, +1920:158) and the Red-eyed Vireo (Tyler, 1912:230; Bent, 1950:342). In +every instance the body feathers of the swaying birds were sleeked. +Courtship behavior in any species of North American vireo seems +closely to resemble that of any other; pairing and nestbuilding of a +female _V. solitarius_ and a male _V. flavifrons_ as reported by +Hauser (1959:383) support the idea of close resemblance. + +A marked similarity will be detected between certain basic elements of +aggressive and epigamic displays. These basic elements are wing- and +tail-flicking, tail-fanning, and high-intensity delivery of the +_chee_. Pouncing and supplanting attacks are essentially similar. Such +similarities suggest either a common origin for certain aggressive and +epigamic displays or the derivation of one from the other. + +High-intensity _cheeing_ is obviously a function of excitement, +whether in conjunction with hostility or sexual behavior. According to +Andrew (1956:179), flicking of wing and tail in passerines are +intention movements of flight. These actions have been emancipated +from incomplete take-offs and incorporated in ritualized courtship and +agonistic behavior. In incipient courtship behavior the male is +governed by three conflicting tendencies; to flee, to attack, or to +behave sexually before his mate (Tinbergen and Hinde, 1958:256). When +pairing, Bell Vireos interrupt sexual chase with "greeting +ceremonies," the male's tendency to attack and the female's tendency +to flee are momentarily reduced, and the forming bond is strengthened. +Thus, the intention movements become an integral part of courtship. + +In situations where attacking and fleeing are the two conflicting +tendencies, wing-flicking and tail-flicking are incorporated into +threat display, but do not lose all of their original function, for +they facilitate attack. Tail-fanning, as a display element, increases +the awesome aspect of the threatening bird and in courtship presumably +makes the sexes more attractive to one another. + +Courtship feeding has not been recorded for the Bell Vireo. In +general, it is unknown in North American vireos, with the exception of +the red-eye (Lawrence, 1953:53). It would serve no "practical" purpose +in the Bell Vireo since the male regularly relieves the female during +incubation, thus allowing her ample opportunity to forage. In the +Red-eyed Vireo, only the female regularly incubates, and courtship +feeding is definitely functional. Nolan (1960:228) described a brief +pecking or pulling with their bills between pairing birds. This may be +incipient "symbolic" courtship feeding, or perhaps mutual preening. + + + + +SELECTION OF NEST-SITE AND NESTBUILDING + + +As far as can be determined, the nest-site is selected by the female. +Typically, the pair makes short, low-level flights from tree to tree +with the female invariably in the lead. The birds usually forage +within each tree; the female interrupts this activity to inspect small +forks of low, pendant branches and the male occasionally pauses to +sing. The singing is loud but not particularly regular, as it is later +when the male accompanies the female during actual nestbuilding. +Method of selection of site resembles that described by Lawrence +(1953:53) for the Red-eyed Vireo. + +Nests are suspended from lateral or terminal forks about 27 inches +high in bushes and small trees that, in the study area, averaged 11 +feet, four inches in height (Table 5). The height above ground of the +nests does not vary appreciably as the season progresses as is the +case with nests of Red-eyed Vireos, for which Lawrence (1953:54) noted +that late nests were placed higher than those built earlier in the +season. + +Most nests are so situated that they are protected and concealed by +the dense foliage of trees. Where nests are placed in low bushes, as +coralberry or dogwood, the bush is invariably overhung by the foliage +of a much taller shrub or tree. + +The nest tree or shrub was in every instance situated at the edge of a +thicket or isolated from adjacent trees by several feet. Preference +for open situations is characteristic of the species. In contrast, the +nest of the White-eyed Vireo (Bent, 1950:229) is placed toward the +center of thickets. + +In the choice of sites in the study area, the Bell Vireos were almost +unopposed by other avian species, owing to the size of the fork +utilized and the fact that the nests are located peripherally, rather +than centrally, in the bush or tree. This lack of competition for a +nest-site provides a Bell Vireo with an ample supply of nest-sites +within any one territory. + + TABLE 5. NEST-SITES UTILIZED IN 1960. + + ==================================================================== + | Number | Average | Average + Plant | of | height of | height of + | nests | plant | nest + -----------------------------+--------+---------------+------------- + _Ulmus americana_ | 4 | 7 ft. 6 in. | 2 ft. 3 in. + _Maclura pomifera_ | 20 | 13 ft. 11 in. | 1 ft. 11 in. + _Crataegus mollis_ | 1 | 11 ft. | 3 ft. 1 in. + _Gleditsia triacanthos_ | 2 | 15 ft. 6 in. | 1 ft. 9 in. + _Acer negundo_ | 4 | 8 ft. 9 in. | 2 ft. 5 in. + _Cornus drummondi_ | 2 | 8 ft. | 2 ft. 8 in. + _Symphoricarpos orbiculatus_ | 3 | 3 ft. | 1 ft. 10 in. + | | | + 7 | 36 | 11 ft. 4 in. | 2 ft. 3 in. + -----------------------------+--------+---------------+------------- + +Selection of the first nest-site may take as long as two days, +possibly owing to incomplete development of the nesting tendency, but +more likely to a general lack of familiarity with the territory. +Red-eyed Vireos require five to six days to choose the first nest-site +(Lawrence, 1953:54). Later sites of the Bell Vireo are chosen in as +little as three hours. Nest 1-c (1960) was abandoned at about 11:00 +a.m. on May 14, 1960, when part of the thicket on the edge of which +this nest was located was removed by brush-cutters clearing a power +line right-of-way. By 2:00 p.m. this pair had begun construction of +1-d (1960) in an Osage orange 110 feet southwest of 1-c (1960). + +This particular site is of further interest because it is the same one +utilized for nest 1-a (1960). In all, four instances of utilization of +a nest-site a second time were recorded. Two-a (1960) and 2-d (1960) +were built in the same fork; 1-c (1960) and 1-h (1960) were in the +same tree, but not the same fork. It should be mentioned that 1-a +(1960) and 2-a (1960) were abortive attempts that did not progress +beyond the suspension apparatus. Nice (1929:16) recorded a similar +instance of the re-use of a nest tree, but different forks were used. + +Re-use of an exact nest-site would ordinarily be impossible if the +initial attempt were not abortive, because the presence of a completed +nest would pose problems in construction with which the birds would +probably be unable to cope. (A report by Morse in Bent, 1950:256 of a +double nest indicates that this may not always be true. At the time of +discovery one nest contained two eggs and the other nest contained +young.) Since nests are used only once there would be no tendency to +adopt the old nest. However, abortive nests, usually little more than +a few strands of nesting material secured to the fork, might stimulate +the birds to continue building. Re-use of a single nest-site in 15.8 +per cent of 38 nests built in 1960 seems to be more than fortuitous +circumstance. This re-use may have physiological benefits in +conjunction with apportionment of energy for other nesting activities, +because rapid location of a nest-site would mean that energy normally +expended in searching and selecting could be rechanneled for actual +construction. In each of the instances of rebuilding, the new nest +was begun on the same day that the previous nest was abandoned. + +The re-nesting of pair 9 (1960) is worthy of note. These birds were +established in the elm thicket on Clark land. Elm was by far the most +abundant tree, with dogwood, Osage orange and honey locust also +relatively common. There were only six boxelders in the territory and +yet the four nests built by this pair were placed in them. This is the +only instance of seeming preference. + + +_Building_ + +Nestbuilding by Bell Vireos can be best discussed in terms of the +phases of construction described for the Red-eyed Vireo, Lawrence +(1953:57), which are: (1) construction of the suspension apparatus, +(2) construction of the bag, (3) lining of the bag and smoothing and +polishing of the exterior, and (4) adornment of the exterior. Red-eyes +(Lawrence, 1953:59) may continue adornment far into the period of +incubation. Both the male and female Bell Vireo have been observed to +add spider egg sacs and other silk to the exterior of the nest as late +as the sixth day of incubation. + +Nice (1929:16) recorded only the female Bell Vireo building, but she +did recall, from previous studies, having seen males aiding somewhat. +Pitelka and Koestner (1942:102) wrongly concluded that the female Bell +Vireo builds unaided, but Hensley (1950:243) observed that both sexes +participated in nestbuilding, and Mumford (1952:229) reported two +instances of building by both adults. His description of the +activities viewed in mid-May suggest that they were of the +transitional period between the first and second phases. On the second +occasion he recorded both adults building during the second phase. +Since no details accompany this second observation I assume that it +pertained to activity not necessarily typical of this phase of +construction. Whereas both sexes of the Bell Vireo cooperate in +building the nest, only the female Red-eyed Vireo builds according to +Lawrence (1953:56). But Common (1934:242) saw both Red-eyed Vireos +building a nest. + +The suspension apparatus is constructed by only the male on the first +day. He punctuates each trip to the nest with song. The single song +phrase is given from three to eight times when the male, carrying +nesting material in his bill, arrives in the tree. Typically, he +alights on several perches within the nest tree before flying to the +nest. He often interrupts his work with several songs; when he has +finished adding a load of material he sings from several perches +within the nest tree before departing. The male periodically stops +building to court the female. + +In eight hours (494 minutes) of observing the first phase of +construction at five different nests, I saw the female come to the +nest 28 times; the male made 95 trips. The female came alone only +once, and brought nesting material ten times, but did not build; on +the other 18 occasions her visits were brief and she usually confined +her activities to an inspection of the nest. Twenty of the visits by +the female were made late in the first phase, marking a gradual +transition to her assumption of building responsibility. (The delay by +the female in beginning to build is puzzling; because all evidence +indicates that she helps select the nest-site, I would expect her to +help with the initial building. There seems to be no clear advantage +in her delay in beginning to build.) The courtship and building +activities of the male plus the presence of a partly completed nest +seem to stimulate the female to commence building. Her visits become +more frequent as construction of the suspension apparatus nears +completion. At a time early in the second day the transition has taken +place, and the female becomes the sole worker. + +On May 7, 1960, male 2 (1960), at the time unmated, was observed as he +came upon a nest of the previous year. The nest, after a year's +weathering, suggested in appearance perhaps an early second-day nest. +The bird flew to the nest and tugged and wove loose strands of grass +for three minutes. Before leaving the site, the bird sang twice from +different perches. This observation suggests that a partly constructed +nest can elicit nestbuilding behavior, even in an unmated male. + +The techniques of building by the male consist primarily of laying +pieces of grass or bark across the fork, or along one of its branches, +and then fastening them in place with pieces of animal silk. Once a +"racket" has been formed, spider egg cases and plant down are emplaced +among the fibers. The male employs weaving, twisting, and pecking +motions of the head to emplace material. + +As previously indicated, the female is the principal worker in the +second and third phases of construction. The male infrequently visits +the nest, but regularly visits the nest tree. The molding of the bag +is accomplished by piling leaves, grasses and plant down onto the +suspension apparatus. This material is also bound in with animal silk. +As the amount of material accumulates, the female begins to trample it +and gradually the bag takes shape. When trampling is first attempted, +the nest often fails to support the female and she falls through the +bottom of the nest. Such an occurrence was observed on May 23, 1960, +on three consecutive trips by female 1 (1960), in constructing nest +1-e (1960). As the bag deepens, additional strands of grass are added +to the wall and woven into place. + +The male is extremely attentive during this and the following phase. +He follows the female as she gathers nest-material accompanying both +this activity and her building with rapid song; he may give an average +of seven song phrases per minute. The male brings to the nest a strand +of grass, or some other material, about every twentieth trip. He +frequently inspects the nest and the activities of the female from +perches near the nest. Construction of the bag is ordinarily completed +in the third day. + +The third phase, the lining of the interior and the smoothing of the +exterior, involves an additional one and one-half to two days. +Smoothing of the exterior refers to tightening of the grasses woven +into the bag and addition of more animal silk. In lining the nest, the +female stands on one of the branches of the fork and emplaces one end +of a long, thin strand of some relatively stiff piece of grass or +strip of bark. She then jumps into the bag and, while slowly turning +around, pecks it into place, thus coiling the strand neatly around the +interior of the bag. + +As previously mentioned, the fourth phase overlaps the periods of +lining, smoothing, egglaying, and incubation. The principal activity +is the addition of white spider egg sacs to the exterior. The trips +are infrequent; but, occasionally, birds will interrupt an hour of +incubation with three or four minutes of active adornment, during +which several trips may be made. Both sexes participate in this phase. + + +_Gathering of Nesting Material_ + +Nesting materials were gathered anywhere within the territory. +Occasionally materials were collected from within the nest tree, but +usually they were obtained 20 to 200 feet from the nest-site. On +several occasions I observed birds inspecting stems or branches where +bark was frayed. Loose ends are grasped in the beak and torn free with +an upward jerk of the head. Possibly the notch near the distal end of +the upper mandible aids in grasping these strands. Plant down is first +extracted and then rolled into a ball by means of the beak while held +with the feet before being transported to the nest. + + +_Length and Hours of Nestbuilding_ + +As indicated by Nolan (1960:230), accurate determination of the length +of nestbuilding is difficult because of continued adornment and +polishing after the nest is functionally complete. Most of the early +nests for which I have records took from four and one-half to five +days to construct. A four-to five-day period of building is reported +by other observers (Nice, 1929:16; Pitelka and Koestner, 1942:99; +Hensley, 1950:242; Nolan, 1960:230). + +One instance of protracted building was recorded. Nest 6-d (1960) was +begun on May 29, 1960, and not completed until nine days later on June +6, 1960. In contrast nest 1-g (1960) begun on May 31, 1960, was +finished three days later on June 2, 1960. Nestbuilding occurs between +the hours of 6:00 a.m. and 5:30 p.m. Heavy rain in the early morning +may delay building. + + +_Abortive Nestbuilding Efforts_ + +Eight of 38 nests started in 1960 were never completed (Table 6). Six +of these abortive attempts were abandoned during, or shortly after, +the completion of the suspension apparatus. Five of these nests were +abandoned because the female did not begin building following the end +of work by the male. The early abandonment of the other three nests +1-a (1960), 2-c (1960) and 6-e (1960) was attributable to the +interruption of building by the male because of heavy rain and +protracted territorial conflicts. The occurrence of these abortive +nests at any time within the nesting efforts of a single pair +indicates that such attempts are not examples of "false nestbuilding." + + +_Renesting_ + +Renesting after desertion or successful fledging occurs within two to +thirty-six hours. Young were fledged from 1-a (1959) on June 19, 1959, +and nest 1-b (1959) was discovered when late in the second phase of +construction on June 22. If the nest was started on June 20, then +renesting took place within 15 hours after fledging. + + +_The Nest_ + +Several authors have described various aspects of the nest of the Bell +Vireo, notably Goss (1891:535); Simmons (_in_ Bent, 1950:256), Nice +(1929:13) and Nolan (1960:230-231). I can add but little to these +descriptions. + +The nest itself is a compact structure composed of strips of bark and +strands of grasses that are interwoven and tightly bound with animal +silk. The floor of the cup is first lined with a layer of small leaves +and then the entire interior is lined with fine stems or strips of +bark. Feathers are occasionally used to pad the bottom prior to +lining, as are pieces of wool and milkweed down. Nest 2-e (1960) had +been packed with small pieces of soil bearing moss prior to lining. + + TABLE 6. ABORTIVE NESTING ATTEMPTS IN MAY AND JUNE OF 1960. + + ================================================== + Nest | Length | Cause of abandonment + | of time | + | worked on | + -----+-----------+-------------------------------- + 1-a | 1 day | Heavy rain + 1-h | 2 days | Female failed to build + 2-a | 1/2 day | Female failed to build + 2-c | 1 day | Protracted territorial dispute + 4-a | 1 day | Female failed to build + 5-a | 1 day | Female failed to build + 6-c | 1 day | Heavy rain + 7-a | 2 days | Female failed to build + -----+-----------+-------------------------------- + +Early nests tend to be bulkier, having thicker walls and bottoms than +later efforts. However, nests in May were found to have 16 per cent +thicker bottoms and 41 per cent thicker walls than nests in June +(Table 7). Standard nest measurements do not show this to be so, for +the exterior and interior diameters at the rim are governed by the +angle between the two branches of the fork. + + TABLE 7. DIMENSIONS OF NESTS IN MAY (1960) AND JUNE (1960). + + ======================================================== + Measurements | May (N 10) | June (N 8) + ------------------------+---------------+--------------- + External depth | 61.6 mm. | 59.3 mm. + Depth of cup | 45.5 mm. | 46.3 mm. + Outside diameter | 57.3/55.5 mm. | 54.3/53.5 mm. + Inside diameter | 43.4/42.2 mm. | 45.5/43.9 mm. + Thickness of forward | | + wall 1 inch below rim | 13.8 mm. | 7.6 mm. + Thickness of bottom | 11.3 mm. | 4.6 mm. + ------------------------+---------------+--------------- + + + + +EGGLAYING AND INCUBATION + + +_Egglaying_ + +Egglaying begins the first or second day after completion of the nest. +The female sits in the nest occasionally for periods of five to +twenty-five minutes on the day the nest is completed. This is +interrupted by periods of nest-adornment and foraging; such activities +sometimes keep the female off the nest for several hours. Prior to the +laying of the first egg, only the female is seen on the nest, +although the male is often seen sitting quietly within the nest tree a +few feet from the female. The infrequency of the "congested" song and +the alarm (_eh-eH-EH_) after the inception of "broodiness" indicates +the waning of courtship behavior. As later in incubation only the +"normal" song and the scold are heard. + +Eggs are laid early in the morning prior to 5:30 a. m. according to +Nolan (1960:232). The nest is usually left unoccupied for considerable +periods after the first egg is laid, but, on the first day of laying, +both sexes have been observed sitting for brief periods averaging ten +minutes in length. Eggs are laid at one-day intervals until completion +of the clutch. I found incubation to begin with the second egg. + + +_Clutch-size_ + +The average clutch-size of the Bell Vireo in Kansas, based on +thirty-three records, is 3.39 eggs (Table 8). Seasonally, the largest +average clutches are produced in the middle of the breeding season, +that is, in June. Lack (1947:308-309) indicates that in European +passerines the highest seasonal average clutch-sizes likewise occur in +June. The largest average clutch-size in the Bell Vireo is presumably +related to some aspect of the availability of food. + + TABLE 8. AVERAGE NUMBERS OF EGGS PER NEST (NUMBER OF RECORDS + IN PARENTHESES)[F]. + + ======================================================== + | | | | Mean + Year | May | June | July | annual + | | | | clutch-size + ----------+---------+----------+---------+-------------- + 1959 | 3.0 (7) | 3.2 (12) | 3.0 (1) | 3.06 + 1960 | 3.3 (6) | 3.83 (5) | 4.0 (2) | 3.72 + ----------+---------+----------+---------+-------------- + 1959-1960 | 3.17 | 3.52 | 3.5 | 3.39 + ----------+---------+----------+---------+-------------- + + [F] These data have been supplemented from the literature + pertinent to Kansas. + +Caution is necessary in determining mean clutch-size in the Bell +Vireo. Eggs occasionally disappear from the nest prior to or during +incubation, without subsequent addition of cowbird eggs. Unfamiliarity +with the history of such a nest on the part of the observer would lead +to an inaccurate determination of clutch-size. + +Complete clutches are not replaced with the same regularity as are +nests. I have recorded intervals of six to thirty days between +successive clutches. Successful replacement of clutches is determined +by a number of factors: nest-site, completion of a nest, weather, +predation, and parasitism by the cowbird. The difference between the +number of renesting attempts and the successful replacement of +clutches seems to indicate that different physiological processes are +responsible for these two phenomena and that there is lack of +synchrony between them. The development of the ovarian follicle +requires a specific number of days that is not always coincident with +the building of replacement nests. If, in the Bell Vireo, replacing a +nest were solely a responsibility of the female, instead of involving +the male to a considerable extent, it would seem likely that +replacement of nests and the replacement of clutches would be more +closely coordinated. + + +_Incubation_ + +Nice (1954:173) considers the incubation period to be the elapsed time +between the laying of the last egg in a clutch and the hatching of +that egg, when all eggs hatch. My data indicate that, normally, +intensive incubation begins when the second egg is laid and lasts +fourteen days in the Bell Vireo. Nice (1929:99) also considered the +incubation period in this species to be fourteen days but believed it +to commence when the third egg was laid. Pitelka and Koestner +(1942:99) noted that the first and second eggs hatched fourteen days +after laying of the second egg. However, they thought incubation began +with the first egg. This would mean a fifteen-day period for this egg. +All the eggs that Nolan (1960:234) marked hatched in approximately +fourteen days. Eight eggs artificially incubated by Graber (1955:103) +required an average of 15.01 days to hatch. As Van Tyne and Berger +(1959:293) indicate, periods of sitting on the nest, even all night, +do not necessarily mean that incubation has begun, for it has been +demonstrated in several species that birds may sit on an egg without +actually applying heat. My own observations demonstrate that the first +egg may be left unattended for several hours at a time on the day that +it is laid. + + +_The Roles of the Sexes in Incubation_ + +Both the male and female sit on the eggs in the daytime. My study of +histological sections of ventral epidermis indicates that the male +does not possess a brood patch; the increased vascularization typical +of the brood patch in females is not evident in males. But, the male +loses most of the down feathers of the ventral apterium. Also, +according to Bailey (1952:128), the male Warbling Vireo that sits on +the eggs lacks a brood patch. + +Bailey (1952:128) suggests that male passerines lacking brood patches +that habitually sit on eggs do not heat the eggs. Thus it cannot be +considered true incubation since no increase of temperature in the +eggs is effected by such means. He further notes that it is at night +when eggs are likely to experience a drop in temperature that +embryonic development will be impaired. I have no data directly +pertaining to which sex sits at night, but it is presumably the +female, because she is always seen on the nest early in the morning +and late in the evening. + + [Illustration: FIG. 4. Comparison of periods of incubation + by both sexes in cold (54° F.) rainy weather (A) and in warm + (82° F.) sunny weather (B).] + +If a highly-vascularized brood patch is essential for true incubation, +then it is surprising that males take regular turns on the nest in +cold, rainy weather. On May 20, 1960, male 3 (1960) sat on the eggs +longer than did the female (fig. 4). The temperature during this hour +and a half of incubation was 54° F. One solution to this problem is +supplied by Skutch (1957:74). He indicates that, "the type of the +incubation is determined largely by innate factors, so that it +persists through fairly wide fluctuations in weather, although it may +break down in extreme conditions." Obviously then, in the example +described above, the weather conditions do not qualify as "extreme." +Sitting by the male is certainly functional to some extent for it +relieves the female to forage; furthermore, the eggs are sheltered +from inclement weather and protected from predators. Nolan (1960:232) +suggests similar reasons for incubating by the male and adds the +"conservation of heat supplied to the eggs by the female." + + [Illustration: FIG. 5. Daily participation in incubation as + indicated by the sex of the adult on the nest upon approach of + the observer.] + +My data, based on incubation beginning with the second egg, indicate +that the female incubates more often daily than the male (fig. 5). The +male sits on the eggs only occasionally in the morning, but almost as +often as the female in the afternoon. Nolan (1960:233) found that 95.5 +per cent of the male's time on the nest and only 40 per cent of the +female's time were attributable to the early hours of the day. +Although I lack data on the critical hours of 5:00 a.m. to 6:59 a.m., +I have enough observations (20) from 7:00 a.m. to 9:00 a.m. to +indicate that the males sit on the eggs infrequently (3 of 20 +instances) in those hours. The discrepancy in the two sets of data, +which may be merely an artifact of sampling techniques, does suggest +two possible alternatives: (1) the male sits on the eggs in the +morning and gives the female, who sits on the eggs throughout the +night, an extended rest and an opportunity to forage; (2) the female +continues to sit throughout the morning, especially during the early +hours of daylight, a time of day when the temperature may still be low +enough to impair development of the embryo. + + +_Relief of Partners in Incubation_ + +Relief of partners involves some ceremony. When the female is +incubating, the male sings several times as he approaches the nest +tree; the female responds with several _chees_, but otherwise remains +immobile. The male sings several more times upon alighting in the nest +tree whereupon the female _chees_ again and flies directly from the +nest. A few seconds later the male appears at the edge of the nest +and, after inspecting the eggs, hops in and settles upon them. When +the male is sitting he is notably anxious prior to an exchange with +the female, often arising and craning his neck as he surveys the +surrounding vegetation, seemingly searching for his mate. The singing +of the male and the calling of the female serve as signals, +coordinating the exchange. + + + + +NESTLING PERIOD + + +_Hatching Sequence_ + +As indicated earlier, hatching normally occurs fourteen days after the +second egg is laid. Hatching of the young was staggered at three nests +under observation. In nest 2-b (1959) the first young hatched on June +8, 1959, the second on June 10. In 3-b (1959) one young hatched each +day from the 12th through the 14th of June. In 5-a (1959) two young +hatched on June 15, the third on June 16, and the fourth on June 17. +Size of the young differed notably for about three days as a result of +staggered hatching, but after that day the younger birds tended to +catch up in size with their older brood-mates. The fourth young in +nest 5-a (1959) grew steadily weaker and was missing from the nest on +June 23, 1959. Staggered hatching is usually thought to be related to +the availability of food that will insure survival of at least some of +the nestlings when a shortage of food exists. It is doubtful that +staggered hatching has adaptive significance in the Bell Vireo, since +there seems to be no shortage of food for the young. In small +passerines such as the Bell Vireo the principal problem is to insure +fledging as quickly as possible because of the danger from predators. + + + +_Development of the Nestlings_ + +Young are pinkish at hatching and devoid of visible natal down. Du +Bois (_in_ Wetherbee, 1957:380), inspected day-old nestlings by means +of a magnifying glass and was unable to detect any down. Nolan +(1960:236) also indicates that the young are naked at birth and that +the "body color is between flesh and rufous except where folds of the +straw yellow skin obscure the underlying colors." The Hutton Vireo +(_Vireo huttoni_) is essentially naked at birth, save for sparse +hairlike down on the head and back (Wetherbee, 1953:380). The Red-eyed +Vireo, according to Lawrence (1953:67) is naked at birth save for a +sparse covering of greyish natal down, on the head, shoulders, and +back. + +In the Bell Vireo the pterylae darken slightly on the second day and +the color becomes more intense daily until the quills of the dorsal +tracts, the wings, and the tail break from their sheaths on the sixth +day. In Red-eyed Vireos the pterylae darken by the end of the first +day and the quills break through the skin on the fifth day, erupting +from the sheaths by the seventh day (Lawrence, 1953:67). + +From the first day the young are able to squeak. Poking a young bird +was sufficient to elicit this sound, phonetically a nasal _peek_. The +only other vocalization noted throughout the nestling period was an +abbreviated _chee_. + +For the first three days tapping the nest or even movement of it +caused by wind would elicit begging. By the fifth day at nest 2-a +(1959) only vigorous agitation of the branch to which the nest was +attached evoked any response. At this nest on June 16, 1959, one young +begged while the other cowered. Cowering is correlated with opening of +the eyes, as the young bird that begged had its eyes only partly open. +Both young cowered on June 19, 1959. Table 9 summarizes the maturation +of the nestling Bell Vireos. + + TABLE 9. MATURATION OF NESTLING BELL VIREOS. THE FIRST DAY + THAT AN ACTIVITY WAS OBSERVED IS SHOWN. + + ================================================================== + | Day of nestling life + +---+---+---+---+---+---+---+---+---+----+---- + | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 + --------------------+---+---+---+---+---+---+---+---+---+----+---- + | | | | | | | | | | | + Eyes open | | | | x | | | | | | | + Feathers erupt | | | | | x | | | | | | + Sound: Squeak | x | | | | | | | | | | + _Chee_ | | | | x | | | | | | | + Begging | x | | | | | | | | | | + Cowering | | | | | | | | x | | | + Head scratching and | | | | | | | | | | | + Preening | | | | | | | | | x | | + Hopping to rim of | | | | | | | | | | | + nest | | | | | | | | | x | | + Fledging | | | | | | | | | | |x[G] + --------------------+---+---+---+---+---+---+---+---+---+----+---- + + [G] This is the commonest fledging day. + + +_Parental Behavior_ + +No eggshells were found in nests on the days of hatching. Presumably +they had been removed by the parents. Nolan (1960:234) indicates +immediate disposition of the eggshell after hatching. Lawrence +(1953:62) suggests that conspicuous removal of eggshells by the female +Red-eyed Vireo informs the male that the young have hatched. + +Both sexes brood and the exchange of partners resembles that described +for the incubation period. Decrease in brooding in the daytime begins +about the sixth day of nestling life. Nolan (1960:235) reports a sharp +decrease in brooding when the oldest nestlings are seven days old. +Brooding decreases notably on the sixth day of nestling life in the +Red-eyed Vireo (Lawrence, 1953:62). Nice (1929:17), Hensley +(1950:244), and Nolan (1960:235) report that the female Bell Vireo +assumes a slightly greater role in brooding than the male. + +Apparent sun-shading was noted at nest 3-b (1959) at 2:00 p.m. on +June 17, 1959, on the fifth day of the nestling period. The nest +contained three young. An adult flew to the nest; while standing on +its rim the bird dipped its head into the nest six times, afterward +appeared to be eating a fecal sac, than shifted position to the +unattached portion of the rim, gaped three times, thereupon spread its +wings, and sat motionless 35 minutes. In this attitude it formed an +effective shield sheltering the young from direct sunlight penetrating +the thin foliage of the honey locust in which the nest was situated. +The temperature at this time was 95° F., but the sky was partly +cloudy. By 2:30 p.m. the sky had become overcast and the sun passed +behind a cloud. Although sunlight no longer fell directly upon the +nest, the bird remained in the shielding posture for another five +minutes before flying from its perch. Sun-shading was not observed at +either of the other nests containing young; dense overhead vegetation +protected those nests. Sun-shading has been noted in other species +where the nest was poorly protected from the sun. Lawrence (1953:62) +observed this behavior at two Red-eyed Vireo nests in conifers. The +"sun-shield" posture of the Bell Vireo does not correspond to any of +the sunning postures described by Hauser (1957). + + +_Feeding of the Nestlings_ + +Both sexes fed the young, and presumably began shortly after the first +nestling hatched. My data indicate that the female does more feeding +than the male (Table 10); in about eight hours of observation a total +of 67 morsels were brought, 43 by the female and 24 by the male, for +an average of once every 7.6 minutes. Nice (1929:17), however, +observed a male to bring food 53 times as compared to 21 visits by the +female. In five and one-half hours of watching, meals were brought +once every 4.9 minutes. Du Bois (_in_ Bent, 1950:257) recorded seven +trips in an hour and forty minutes, or one every fourteen minutes. + +At three nests containing young the adults were sometimes silent and +sometimes vocal on their approach. The female often emitted a subdued +_chee_ which, coupled with the vibration of the nest caused by her +arrival, elicited begging behavior from the young. None of the males +was heard to utter such a call, but I have the impression that they +often did call although I failed to hear the sounds. The males did, on +occasion, sing several songs as they approached, even with food held +in their beaks. Such singing elicited begging from the nestlings. Once +the eyes of the young were open they often began begging when a silent +adult was within two or three feet of the nest; begging behavior +probably is elicited by tactile, auditory or visual stimuli in that +order, or, as the nestling period proceeds, by any combination of +these stimuli. + + TABLE 10. FEEDING OF THE NESTLINGS. + + ==================================================== + Day of | Length of | Adult involved + nestling period | observation +---------+--------- + | | Male | Female + -----------------+--------------+---------+--------- + 1 | 30 min. | 3 | 5 + 2 | 60 min. | 1 | 4 + 3 | 60 min. | 2 | 5 + 4 | 30 min. | 1 | 4 + 7 | 60 min. | 4 | 7 + 2 | 60 min. | 3 | 3 + 6 | 60 min. | 3 | 6 + 7 | 30 min. | 3 | 3 + 9 | 60 min. | 4 | 6 + +--------------+---------+--------- + Totals | 510 min. | 24 | 43 + -----------------+--------------+---------+--------- + +Not all trips made by parents resulted in successful feeding of young; +some visits seemed to be purely for inspecting the young. On other +occasions the adults experienced difficulty in transferring food to +the young, and, thus thwarted, would themselves eat the food. Nice +(1929:17) estimated that from five to twelve of a total of +seventy-five meals were eaten by adults. + + +_Nest Sanitation_ + +Both parents regularly removed fecal sacs from the nest, eating them +for the first five days and thereafter carrying them off and +presumably dropping them. It is doubtful that fecal sacs were actively +removed in the last two days of nestling life as the bottoms of nests +from which young flew away were invariably covered with excrement. + +On several occasions a parent brought food to the nest and then +remained perched on the rim alternately peering into the nest and then +preening. Once bill swiping was observed and another time an adult +male sang once. The adult remained at the nest from twenty seconds to +a full minute. + + +_Fledging_ + +Eight young were fledged from the four nests in 1959. The nestling +period lasted from nine to twelve days. Human interference may have +been largely responsible for the fledging of the young at nine days. +Pitelka and Koestner (1942:100) found nestling life to last eleven +days. Nolan (1960:235) reports nestling periods varying from 10.5 to +12 days. The young Red-eyed Vireo is ready to leave the nest at ten +days but often remains an additional day before departing (Lawrence, +1953:68). + +The oldest nestling at nest 2-a (1959) hopped out on June 17, 1959, +when I disturbed the parents. On this date the juvenal plumage was +only partly developed and the young bird was incapable of flight. By +the tenth day of nestling life the young in all the nests were +observed to hop to the rim, flutter their wings, hop back into the +nest and also to preen and scratch their heads. The young at fledging +are usually completely feathered, but have notably short tails and +relatively short, stubby wings. According to Ridgeway (1904:205) the +juvenal plumage is much like that of the adult. + + +_Nest Parasites_ + +Pitelka and Koestner (1942:103) found that incubating adults and later +the young suffered infestation of the northern fowl mite, +_Ornithonyseus sylviarum_. Nolan (1960:241) reports a heavy +infestation of this mite at four nests. Unidentified mites were noted +at four nests in my study area in 1959. Incubating adults were +observed to peck at their breasts and scapulars from the eleventh +through the fourteenth day of incubation. Serious infestations were +not noted at the nests until the ninth day of nestling life. At this +time the young were observed to scratch their heads and peck at their +breasts, scapulars, and the base of their tails. On the day of +fledging the nests were a seething mass of crawling mites; the mites +also extended well up the branches to which the nests were attached. +Nest 1-a (1959), which was discovered on June 18, 1959, presumably on +the day after fledging, was densely covered with mites. Some mites +were still crawling on this nest on June 20, 1959. + + + + +FLEDGLING LIFE + + +On June 20, 1959 I located one young 80 feet northeast of nest 2-a +(1959), about five hours after it had left the nest. One parent was +observed to feed it once. No young were seen thereafter from this or +any other nest. Extreme agitation on the part of one or both parents +on several occasions shortly thereafter, however, suggested the +proximity of the young. Search in the immediate vicinity on each of +these occasions proved fruitless. Three days after fledging their +young, pair 2 (1959) was primarily occupied with courtship activities. +Pair 1 (1959) was involved in courtship and nestbuilding one and +one-half days after the apparent fledging of their young. Nolan +(1960:238) indicates that the young remain within the territory and +perhaps are fed by the parents up until an age of about 40 days. +Sutton (1949:25) and Lawrence (1953:68) present contradictory reports +on fledgling-parent relationships in the Red-eyed Vireo. Sutton +concluded that the young quickly took leave of their parents whereas +Lawrence reported a young bird being fed 35 days after fledging. + + +_Second Broods_ + +The curve based on 66 nesting records of the Bell Vireo representing +the breeding activity in northeastern Kansas demonstrates a tendency +toward double-broodedness (fig. 6). The peak of the breeding season is +from May 20 to June 20. The large number (20) of replacement nests +built in late May of 1960 tends to distort the curve of the breeding +data; a second peak about 35 days after the first is evident. + +I am of the opinion that the vast majority of vireos are +single-brooded solely by virtue of the limited success of early +nesting efforts, and that in "good" years most pairs would be +double-brooded. Each of the four pairs that successfully raised one +brood in my study area in 1959 renested within a day or two after the +fledging of the young. I do not know the fate of these nests. Nolan +(1960:237) reports at least one instance of a second brood in the +course of his study. Nolan (_op. cit._) notes that the literature, in +general, indicates that vireos are double-brooded, but that his +evidence, mentioned previously, is the only evidence based on banded +birds. + + [Illustration: FIG. 6. Breeding season in northeastern Kansas + based on the number of completed clutches in each 10-day + period from May through July.] + + + + +REPRODUCTIVE SUCCESS + + +Only four nests were successful; all of these were observed in 1959. +The principal external factors responsible for nesting failure were +severe weather, predation, parasitism by Brown-headed Cowbirds +(_Molothrus ater_) and human interference (Table 11). + +In late winter and early spring of 1960 heavy snow, continuously at a +depth of at least 10 inches, covered most of the Mid-west from +February 20 through March 20. Consequently, the growing season was +some two weeks behind that of 1959. Of all the species in the study +area, the Bell Vireo is the most dependent on dense foliage for cover +and concealment for its nests. Consequently the tardiness of the +season seemingly negatively influenced reproductive success of this +more than any other species of bird in the study area. + + +_Behavior_ + +Several aspects of the behavior of the Bell Vireo tend to contribute +to nesting failure. They include: + +1. Nest-site. Nests are occasionally suspended from exposed branches. +Occurrences of this sort suggest that the dimensions of the fork are +more important in the choice of a site than availability of cover. + +2. Song. The loud, continuous song of the male during nestbuilding +alerts cowbirds and predators to the presence of a nest. The +incongruous habits of the male of singing in the nest tree and while +sitting on the nest may facilitate location by some enemies, +particularly cowbirds. + + TABLE 11. EGG MORTALITY IN BELL VIREOS. + + ====================================================== + | | Eggs (N-29)| | + Mortality agents | N[H] | 1959 | N | 1960 + | | Per cent | | Per cent + -----------------+------+------------+-----+---------- + Predation | 4 | 13.8 | 5 | 10 + Weather | 2 | 6.9 | 8 | 16 + Cowbird | 14 | 48.3 | 37 | 74 + +------+------------+-----+---------- + Totals | 20 | 69[I] | 50 | 100 + -----------------+------+------------+-----+---------- + + [H] Number of eggs out of the total number laid lost to + mortality agents. + + [I] In 1959 nine eggs were successful (ultimately gave rise to + fledglings). + +I am not fully convinced that song from the nest is simply a "foolish" +habit, since snakes, the principal predators with which this species +has to contend, are deaf. My own field observations and the +circumstances of the innumerable instances recorded in the literature +of male vireos singing from the nest suggest that this is a function +of the proximity of the observer. As mentioned elsewhere, vocal threat +is the initial as well as the primary means by which territory is +maintained. Song from the nest evoked by an enemy also serves to alert +the female to danger. + +3. Flushing. The Bell Vireo normally relies upon cryptic behavior to +avoid detection at the nest. Most sitting birds, especially the +females, either flush silently when an enemy is about forty feet from +the nest or remain sitting upon the nest tenaciously, refusing to +flush even when touched or picked up. Some birds flushed at +intermediate distances of from three to fifteen feet. In so doing they +revealed the location of their nests. Since none of these +"intermediate flushers" enjoyed nesting success there is possibly some +correlation between these two factors. + + +_Predation_ + +Several complete clutches being incubated disappeared from nests that +were unharmed. Absence of eggshells in the vicinity suggests predation +by snakes. + +On May 25, 1960, I found a _Peromyscus_ climbing toward nest 1-a +(1960). The mouse moved to within two inches of the nest whereupon I +removed the mouse. Such small rodents constitute another potential +source of predation. + + +_Cowbird Parasitism_ + +In this study the failure of 12 of 35 nests can be directly attributed +to cowbird interference. It is well established that the incidence of +cowbird parasitism of Bell Vireo nests is high (Friedmann, 1929:237; +Bent, 1950:260-261). Nolan (1960:240) found only one nest of eight +studied to be parasitized by cowbirds. He indicates that this is +surprising in view of the heavy molestation of the Prairie Warbler +(_Dendroica discolor_) in the same region. A possible explanation of +this phenomenon seems to lie in the much greater abundance of the +Prairie Warbler in comparison to that of the Bell Vireo. In my study +area the incidence of cowbird parasitism on Bell Vireos in 1959 and +1960 greatly exceeded that of all other nesting species that were +parasitized (Table 12). + +As indicated previously, the female Bell Vireo leaves the nest +unoccupied several hours at a time in the transition period between +completion of the nest and the start of egglaying. Such behavior early +in the morning certainly would facilitate deposition of cowbird eggs. +Early in the nesting period the mere presence of a cowbird egg in the +nest prior to the laying of the host's first egg leads to abandonment +of the nest. This seems to be correlated with the relative strength of +the nesting tendency; anyhow cowbird eggs laid in later nests prior to +the appearance of the host's own eggs did not cause the nesting birds +to desert. The Bell Vireo does abandon the nest when all but one of +its own eggs have been removed by the cowbird. Mumford (1952:232) +records the removal of a cowbird egg by the host birds and I recorded +a similar instance involving nest 2-b (1960). On May 14, 1960, I +found one punctured cowbird egg on the ground about 10 feet west of +this nest. Occasionally a cowbird egg is buried beneath the lining of +a nest. Mumford (1952:23) observed this in mid-May in 1951 and I +observed pair 8 (1960) actively covering with building material a +cowbird egg on July 5, 1960. Covering a cowbird egg constitutes +effective removal. Since the egg cannot be turned, an adhesion +develops. + + TABLE 12. INCIDENCE OF COWBIRD PARASITISM OF THE BELL VIREO + COMPARED WITH OTHER PASSERINES IN THE STUDY AREA IN 1959 AND + 1960. + + ========================================================= + | Bell | Other + | Vireo |passerines + --------------------------------------+-------+---------- + Total nests examined containing | | + at least one host egg | 35 | 43 + Total nests parasitized | 24 | 14 + Total number of cowbird eggs | 33 | 23 + Per cent of nests parasitized | 68.6 | 32.6 + Total number of cowbird eggs per nest | .94 | .54 + --------------------------------------+-------+---------- + +The percentage of cowbird eggs hatched in relation to the number laid +is relatively low. For instance, Mumford (1952:231) has only one +record of a young cowbird successfully raised by a Bell Vireo. The +data available in Bent (1950:260-261) also indicate that the +percentage of cowbird eggs hatched is small. The Bell Vireo is less +tolerant of cowbird parasitism than are many of the species so +victimized, but is not so intolerant as the Robin, Catbird, and the +Yellow-breasted Chat (Friedmann, 1929:193). + + + + +SUMMARY + + +1. The behavior of a small population of Bell Vireos was studied in +the spring and summer of 1959 and again in 1960 in Douglas County, +Kansas, and results are compared with previous studies elsewhere. + +2. The Bell Vireo sings more often daily and throughout the nesting +season than do the majority of its avian nesting associates. Six types +of vocalizations are readily distinguishable in the field: primary +song, courtship song, distress call, alarm note, specialized male call +note or _zip_, and the generalized call note or _chee_. + +3. Territories are established in early May and occupied throughout +the breeding season and post-breeding season. The average size of the +territories in 1960 was 1.25 acres. Shifting of territorial boundaries +occasionally occurs after nesting attempts. + +4. Territory is maintained primarily by song, but at least five +aggressive displays are manifest in the early phases of territorial +establishment. These include: (a) vocal threat, (b) head-forward +threat, (c) wing-flicking and sub-maximal tail-fanning, (d) ruffling +and maximum tail-fanning, and (e) supplanting attack. + +5. The precise mechanism of pair-formation in the Bell Vireo is not +known. Early courtship activities are characteristically violent +affairs. Absence of sexual dimorphism suggests that behavioral +criteria are used by the birds in sex-recognition; the male is +dominant and the female is subordinate. + +6. The principal displays associated with courtship include: greeting +ceremonies, "pouncing," "leap-flutter," pre- and post-copulatory +displays, and the posture, copulation. The marked similarity between +elements of courtship display and aggressive display suggests common +origin or the derivation of one from the other. + +7. The nest-site probably is selected by the female. Nests are +suspended from lateral or terminal forks about 2 feet 3 inches high in +small trees and shrubs averaging 11 feet 2 inches in height. + +8. Nestbuilding is intimately associated with courtship and is a +responsibility of both sexes. The male builds the suspension apparatus +and the female constructs and lines the bag. Both sexes participate in +adorning the exterior. Construction lasts from four and one-half to +five days. + +9. The nest is compact, pendant, and composed of strips of bark and +strands of grasses that are interwoven and tightly bound with animal +silk. Nests built in May are bulkier than those constructed later in +the season. + +10. Egglaying begins on the first or second day after the nest is +completed. The eggs are deposited early in the morning. The average +clutch-size of the Bell Vireo in Kansas is 3.39 eggs. + +11. Both sexes sit on the eggs, but only the female truly incubates +because the male lacks a brood patch. Incubation lasts fourteen days. + +12. The Bell Vireo is double-brooded in "good" years. + +13. Nesting failure resulted from severe weather, predation, +parasitism by cowbirds, and human interference. Behavior that +contributes to nesting failure is selection of an unfavorable +nest-site, singing on and near the nest, and the tendency to flush +from the nest in view of potential enemies. + + + + +LITERATURE CITED + + +AMERICAN ORNITHOLOGISTS' UNION + + 1957. Check-list of North American birds. Fifth ed. Baltimore, + The Lord Baltimore Press, The American Ornithologists' + Union, iv + 691 pp. + +ANDREW, R. J. + + 1956. Intention movements of flight in certain passerines, and + their use in systematics. Behaviour, 10:79-204. + +BAILEY, R. E. + + 1952. The incubation patch of passerine birds. Condor, + 54:121-136. + +BENNETT, W. W. + + 1917. Bell's Vireo studies (Vireo bellii Aud.). Proc. Iowa + Acad. Sci., 24:285-293. + +BENT, A. C. + + 1950. Life histories of North American wagtails, shrikes, + vireos and their allies. Smithsonian Inst., U. S. Nat. + Mus. Bull., 197:vii + 411 pp., 48 pls. + +BUNKER, C. D. + + 1910. Habits of the Black-capt Vireo (Vireo atricapillus). + Condor, 12:70-73. + +CHAPIN, E. A. + + 1925. Food habits of the vireos; a family of insectivorous + birds. U. S. Dept. Agric. Bull., 1355:1-44. + +COMMON, M. A. + + 1934. Notes on a Red-eyed Vireo's nest. Auk, 51:241-242. + +COOKE, W. W. + + 1909. The migration of vireos. Bird Lore, 11:78-82, 118-120, + 165-168. + +FITCH, H. S. + + 1958. Home ranges, territories and seasonal movements of + vertebrates of the Natural History Reservation. Univ. + of Kansas Publ. Mus. of Nat. Hist., 11:3:63-326. + +FRIEDMANN, H. + + 1929. The Cowbirds. Charles C. Thomas, Springfield, Illinois, + xviii + 421 pp. + +GOSS, N. S. + + 1891. History of the birds of Kansas. Topeka, Geo. W. Crane & + Co. Printers and Binders. 692 pp. + +GRABER, R. R. + + 1955. Artificial incubation of some non-galliform eggs. Wilson + Bull., 67:100-109. + +HAMILTON, T. H. + + 1958. Adaptive variation in the genus Vireo. Wilson Bull., + 70:307-346. + +HAUSER, D. C. + + 1957. Some observations on sun-bathing in birds. Wilson Bull., + 69:78-90. + + 1959. Notes on pairing and nestbuilding of mismatched vireos. + Wilson Bull., 71:383-384. + +HENSLEY, MAX + + 1950. Notes on the breeding behavior of the Bell's Vireo. Auk, + 67:243-244. + +HINDE, R. A. + + 1952. The behaviour of the Great Tit (Parus major) and some + other related species. Leiden: E. J. Brill, x + 201 pp. + + 1956. The biological significance of the territories of birds, + Ibis, 98:340-369. + +HINDE, R. A., and TINBERGEN, N. + + 1958. The comparative study of species-specific behavior. In + Behavior and Evolution (Yale University Press, New Haven), + pp. 251-268. + +KLUIJVER, H. N. + + 1951. The population ecology of the great tit, Parus m. major + L. Ardea, 39:1-135. + +LACK, D. + + 1947. The significance of clutch-size. Ibis, 89:302-352. + +LAWRENCE, L. DE K. + + 1953. Nesting life and behavior of the Red-eyed Vireo. Can. + Field-Nat., 67:46-77. + +LEWIS, H. F. + + 1921. A nesting of the Philadelphia Vireo. Auk, 38:26-44, + 185-202. + +LINSDALE, J. M. + + 1928. Birds of a limited area in eastern Kansas. The Univ. of + Kansas, Sci. Bull., 18:11:517-626. + +LLOYD, W. + + 1887. Birds of Tom Green and Concho Counties, Texas. Auk, + 4:181-193, 289-299. + +MORRIS, D. + + 1956. The feather postures of birds and the problem of the + origin of social signs. Behaviour, 9:75-113. + +MOYNIHAN, M. + + 1955. Types of hostile display. Auk, 72:247-259. + +MUMFORD, R. E. + + 1952. Bell's Vireo in Indiana. Wilson Bull., 64:224-233. + +NICE, M. M. + + 1929. The fortunes of a pair of Bell Vireos. Condor, 31:13-20. + + 1943. Studies in the life history of the song sparrow. II. The + behavior of the song sparrow and other passerines. Trans. + Linn. Soc. N.Y., 6:328 pp. + + 1954. Problems of incubation periods in North American birds. + Condor, 56:173-197. + +NOLAN, V. + + 1960. Breeding behavior of the Bell Vireo in southern Indiana. + Condor, 62:225-244. + +PITELKA, F. A. + + 1959. Numbers, breeding schedule, and territoriality in + Pectoral Sandpipers of northern Alaska. Condor, + 61:223-264. + +PITELKA, F. A., and KOESTNER, E. J. + + 1942. Breeding behavior of Bell's Vireo in Illinois. Wilson + Bull., 54:97-106. + +RIDGWAY, R. + + 1889. The ornithology of Illinois. Illinois State Nat. Hist. + Survey, 1: viii + 520 pp. + + 1904. The birds of North and Middle America. U.S. Nat. Mus. + Bull., 50, pt. 3; xx + 801 pp. + +SKUTCH, A. F. + + 1957. The incubation patterns of birds. Ibis, 99:69-93. + +SOUTHERN, W. E. + + 1958. Nesting of the Red-eyed Vireo in the Douglas Lake + Region, Michigan. The Jack-Pine Warbler, 36:105-130, + 185-207. + +SUTTON, G. M. + + 1949. Studies of the nesting birds of the Edwin S. George + Reserve. Part 1. The Vireos. Misc. Pub. Univ. Michigan + Mus. Zool., 74:5-36. + +TOWNSEND, C. W. + + 1920. Supplement to the birds of Essex County, Massachusetts. + Mem. Nuttall Orn. Club, No. 5:196 pp. + +TYLER, W. M. + + 1912. A vireo courtship. Bird Lore, 14:229-230. + +VAN TYNE, J., and BERGER, A. J. + + 1959. Fundamentals of ornithology. John Wiley & Sons, Inc., + New York. xi + 624 pp. + +WETHERBEE, D. K. + + 1957. Natal plumages and downy pteryloses of passerine + birds of North America. Bull. Amer. Mus. Nat. Hist., + 113:5:339-436. + + _Transmitted November 8, 1961._ + + + 29-1506 + + + + + UNIVERSITY OF KANSAS PUBLICATIONS + MUSEUM OF NATURAL HISTORY + + +Institutional libraries interested in publications exchange may obtain +this series by addressing the Exchange Librarian, University of Kansas +Library, Lawrence, Kansas. Copies for individuals, persons working in +a particular field of study, may be obtained by addressing instead the +Museum of Natural History, University of Kansas, Lawrence, Kansas. +There is no provision for sale of this series by the University +Library, which meets institutional requests, or by the Museum of +Natural History, which meets the requests of individuals. However, +when individuals request copies from the Museum, 25 cents should be +included, for each separate number that is 100 pages or more in +length, for the purpose of defraying the costs of wrapping and +mailing. + + * An asterisk designates those numbers of which the Museum's + supply (not the Library's supply) is exhausted. Numbers + published to date, in this series, are as follows: + +Vol. 1. + + Nos. 1-26 and index. Pp. 1-638, 1946-1950. + +*Vol. 2. + + (Complete) Mammals of Washington. By Walter W. Dalquest. Pp. + 1-444, 140 figures in text. April 9, 1948. + +Vol. 3. + + *1. The avifauna of Micronesia, its origin, evolution, and + distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in + text. June 12, 1951. + + *2. A quantitative study of the nocturnal migration of birds. + By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June + 29, 1951. + + 3. Phylogeny of the waxwings and allied birds. By M. Dale + Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10, + 1951. + + 4. Birds from the state of Veracruz, Mexico. By George H. + Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7 figures in + text, 2 tables. October 10, 1951. + + Index. Pp. 651-681. + +*Vol 4. + + (Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41 + plates, 31 figures in text. December 27, 1951. + +Vol. 5. + + Nos. 1-37 and index. Pp. 1-676, 1951-1953. + +*Vol 6. + + (Complete) Mammals of Utah, _taxonomy and distribution_. By + Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables. + August 10, 1952. + +Vol. 7. + + *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73 + figures in text, 37 tables. August 25, 1952. + + 2. Ecology of the opossum on a natural area in northeastern + Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp. 305-338, + 5 figures in text. August 24, 1953. + + 3. The silky pocket mice (Perognathus flavus) of Mexico. By + Rollin H. Baker. Pp. 339-347, 1 figure in text. February 15, + 1954. + + 4. North American jumping mice (Genus Zapus). By Phillip H. + Krutzsch. Pp. 349-472, 47 figures in text, 4 tables. April 21, + 1954. + + 5. Mammals from Southeastern Alaska. By Rollin H. Baker and + James S. Findley. Pp. 473-477. April 21, 1954. + + 6. Distribution of Some Nebraskan Mammals. By J. Knox Jones, + Jr. Pp. 479-487. April 21, 1954. + + 7. Subspeciation in the montane meadow mouse, Microtus + montanus, in Wyoming and Colorado. By Sydney Anderson. Pp. + 489-506, 2 figures in text. July 23, 1954. + + 8. A new subspecies of bat (Myotis velifer) from southeastern + California and Arizona. By Terry A. Vaughan. Pp. 507-512. July + 23, 1954. + + 9. Mammals of the San Gabriel mountains of California. By + Terry A. Vaughan. Pp. 513-582, 1 figure in text, 12 tables. + November 15, 1954. + + 10. A new bat (Genus Pipistrellus) from northeastern Mexico. + By Rollin H. Baker. Pp. 583-586. November 15, 1954. + + 11. A new subspecies of pocket mouse from Kansas. By E. + Raymond Hall. Pp. 587-590. November 15, 1954. + + 12. Geographic variation in the pocket gopher, Cratogeomys + castanops, in Coahuila, Mexico. By Robert J. Russell and + Rollin H. Baker. Pp. 591-608. March 15, 1955. + + 13. A new cottontail (Sylvilagus floridanus) from northeastern + Mexico. By Rollin H. Baker. Pp. 609-612. April 8, 1955. + + 14. Taxonomy and distribution of some American shrews. By + James S. Findley. Pp. 613-618. June 10, 1955. + + 15. The pigmy woodrat, Neotoma goldmani, its distribution and + systematic position. By Dennis G. Rainey and Rollin H. Baker. + Pp. 619-624. 2 figures in text. June 10, 1955. + + Index. Pp. 625-651. + +Vol. 8. + + Nos. 1-10 and index. Pp. 1-675, 1954-1956. + +Vol. 9. + + 1. Speciation of the wandering shrew. By James S. Findley. Pp. + 1-68, 18 figures in text. December 10, 1955. + + 2. Additional records and extension of ranges of mammals from + Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M. + Hansen. Pp. 69-80. December 10, 1955. + + 3. A new long-eared myotis (Myotis evotis) from northeastern + Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84. + December 10, 1955. + + 4. Subspeciation in the meadow mouse, Microtus pennsylvanicus, + in Wyoming. By Sydney Anderson. Pp. 85-104, 2 figures in text. + May 10, 1956. + + 5. The condylarth genus Ellipsodon. By Robert W. Wilson. Pp. + 105-116, 6 figures in text. May 19, 1956. + + 6. Additional remains of the multituberculate genus + Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures in + text. May 19, 1956. + + 7. Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp. + 125-335, 75 figures in text. June 15, 1956. + + 8. Comments on the taxonomic status of Apodemus peninsulae, + with description of a new subspecies from North China. By J. + Knox Jones, Jr. Pp. 337-346, 1 figure in text, 1 table. August + 15, 1956. + + 9. Extensions of known ranges of Mexican bats. By Sydney + Anderson. Pp. 347-351. August 15, 1956. + + 10. A new bat (Genus Leptonycteris) from Coahuila. By Howard + J. Stains. Pp. 353-356. January 21, 1957. + + 11. A new species of pocket gopher (Genus Pappogeomys) from + Jalisco, Mexico. By Robert J. Russell. Pp. 357-361. January + 21, 1957. + + 12. Geographic variation in the pocket gopher, Thomomys + bottae, in Colorado. By Phillip M. Youngman. Pp. 363-387, 7 + figures in text. February 21, 1958. + + 13. New bog lemming (genus Synaptomys) from Nebraska. By J. + Knox Jones, Jr. Pp. 385-388. May 12, 1958. + + 14. Pleistocene bats from San Josecito Cave, Nuevo León, + México. By J. Knox Jones, Jr. Pp. 389-396. December 19, 1958. + + 15. New subspecies of the rodent Baiomys from Central America. + By Robert L. Packard. Pp. 397-404. December 19, 1958. + + 16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson. + Pp. 405-414, 1 figure in text, May 20, 1959. + + 17. Distribution, variation, and relationships of the montane + vole, Microtus montanus. By Sydney Anderson. Pp. 415-511, 12 + figures in text, 2 tables. August 1, 1959. + + 18. Conspecificity of two pocket mice, Perognathus goldmani + and P. artus. By E. Raymond Hall and Marilyn Bailey Ogilvie. + Pp. 513-518, 1 map. January 14, 1960. + + 19. Records of harvest mice, Reithrodontomys, from Central + America, with description of a new subspecies from Nicaragua. + By Sydney Anderson and J. Knox Jones, Jr. Pp. 519-529. January + 14, 1960. + + 20. Small carnivores from San Josecito Cave (Pleistocene), + Nuevo León, México. By E. Raymond Hall. Pp. 531-538, 1 figure + in text. January 14, 1960. + + 21. Pleistocene pocket gophers from San Josecito Cave, Nuevo + León, México. By Robert J. Russell. Pp. 539-548, 1 figure in + text. January 14, 1960. + + 22. Review of the insectivores of Korea. By J. Knox Jones, + Jr., and David H. Johnson. Pp. 549-578. February 23, 1960. + + 23. Speciation and evolution of the pygmy mice, genus Baiomys. + By Robert L. Packard. Pp. 579-670, 4 plates, 12 figures in + text. June 16, 1960. + + Index. Pp. 671-690. + +Vol. 10. + + 1. Studies of birds killed in nocturnal migration. By Harrison + B. Tordoff and Robert M. Mengel. Pp. 1-44, 6 figures in text, + 2 tables. September 12, 1956. + + 2. Comparative breeding behavior of Ammospiza caudacuta and A. + maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1 figure. + December 20, 1956. + + 3. The forest habitat of the University of Kansas Natural + History Reservation. By Henry S. Fitch and Ronald R. McGregor. + Pp. 77-127, 2 plates, 7 figures in text, 4 tables. December + 31, 1956. + + 4. Aspects of reproduction and development in the prairie vole + (Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161, 8 + figures in text, 4 tables. December 19, 1957. + + 5. Birds found on the Arctic slope of northern Alaska. By + James W. Bee. Pp. 163-211, plates 9-10, 1 figure in text. + March 12, 1958. + + 6. The wood rats of Colorado: distribution and ecology. By + Robert B. Finley, Jr. Pp. 213-552, 34 plates, 8 figures in + text, 35 tables. November 7, 1958. + + 7. Home ranges and movements of the eastern cottontail in + Kansas. By Donald W. Janes. Pp. 553-572, 4 plates, 3 figures + in text. May 4, 1959. + + 8. Natural history of the salamander, Aneides hardyi. By + Richard F. Johnston and Gerhard A. Schad. Pp. 573-585. October + 8, 1959. + + 9. A new subspecies of lizard, Cnemidophorus sacki, from + Michoacán, México. By William E. Duellman, Pp. 587-598, 2 + figures in text. May 2, 1960. + + 10. A taxonomic study of the middle American snake, Pituophis + deppei. By William E. Duellman. Pp. 599-610, 1 plate, 1 figure + in text. May 2, 1960. + + Index. Pp. 611-626. + +Vol. 11. + + 1. The systematic status of the colubrid snake, Leptodeira + discolor Günther. By William E. Duellman. Pp. 1-9, 4 figures. + July 14, 1958. + + 2. Natural history of the six-lined racerunner, Cnemidophorus + sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figures, 9 + tables. September 19, 1958. + + 3. Home ranges, territories, and seasonal movements of + vertebrates of the Natural History Reservation. By Henry S. + Fitch. Pp. 63-326, 6 plates, 24 figures in text, 3 tables. + December 12, 1958. + + 4. A new snake of the genus Geophis from Chihuahua, Mexico. By + John M. Legler. Pp. 327-334, 2 figures in text. January 28, + 1959. + + 5. A new tortoise, genus Gopherus, from north-central Mexico. + By John M. Legler. Pp. 335-343. April 24, 1959. + + 6. Fishes of Chautauqua, Cowley and Elk counties, Kansas. By + Artie L. Metcalf. Pp. 345-400, 2 plates, 2 figures in text, 10 + tables. May 6, 1959. + + 7. Fishes of the Big Blue river basin, Kansas. By W. L. + Minckley. Pp. 401-442. 2 plates, 4 figures in text, 5 tables. + May 8, 1959. + + 8. Birds from Coahuila, México. By Emil K. Urban. Pp. 443-516. + August 1, 1959. + + 9. Description of a new softshell turtle from the southeastern + United States. By Robert G. Webb. Pp. 517-525, 2 plates, 1 + figure in text. August 14, 1959. + + 10. Natural history of the ornate box turtle, Terrapene ornata + ornata Agassiz. By John M. Legler. Pp. 527-669, 16 pls., 29 + figures in text. March 7, 1960. + + Index Pp. 671-703. + +Vol. 12. + + 1. Functional morphology of three bats: Eumops, Myotis, + Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures + in text. July 8, 1959. + + 2. The ancestry of modern Amphibia: a review of the evidence. + By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text. + July 10, 1959. + + 3. The baculum in microtine rodents. By Sydney Anderson. Pp. + 181-216, 49 figures in text. February 19, 1960. + + 4. A new order of fishlike Amphibia from the Pennsylvanian of + Kansas. By Theodore H. Eaton, Jr., and Peggy Lou Stewart. Pp. + 217-240, 12 figures in text. May 2, 1960. + + 5. Natural history of the bell vireo. By Jon C. Barlow. Pp. + 241-296, 6 figures in text. March 7, 1962. + + More numbers will appear in volume 12. + +Vol. 13. + + 1. Five natural hybrid combinations in minnows (Cyprinidae). + By Frank B. Cross and W. L. Minckley. Pp. 1-18. June 1, 1960. + + 2. A distributional study of the amphibians of the Isthmus of + Tehuantepec, México. By William E. Duellman. Pp. 19-72, pls. + 1-8, 3 figures in text. August 16, 1960. + + 3. A new subspecies of the slider turtle (Pseudemys scripta) + from Coahuila, México. By John M. Legler. Pp. 73-84, pls. + 9-12, 3 figures in text. August 16, 1960. + + 4. Autecology of the copperhead. By Henry S. Fitch. Pp. + 85-288, pls. 13-20, 26 figures in text. November 30, 1960. + + 5. Occurrence of the garter snake, Thamnophis sirtalis, in the + Great Plains and Rocky Mountains. By Henry S. Fitch and T. + Paul Maslin. Pp. 289-308, 4 figures in text. February 10, + 1961. + + 6. Fishes of the Wakarusa river in Kansas. By James E. Deacon + and Artie L. Metcalf. Pp. 309-322, 1 figure in text. February + 10, 1961. + + 7. Geographic variation in the North American cyprinid fish. + Hybopsis gracilis. By Leonard J. Olund and Frank B. Cross. Pp. + 323-348, pls. 21-24, 2 figures in text. February 10, 1961. + + 8. Descriptions of two species of frogs, genus Ptychohyla; + studies of American hylid frogs, V. By William E. Duellman. + Pp. 349-357, pl. 25, 2 figures in text. April 27, 1961. + + 9. Fish populations, following a drought, in the Neosho and + Marais des Cygnes rivers of Kansas. By James Everett Deacon. + Pp. 359-427, pls. 26-30, 3 figs. August 11, 1961. + + 10. Recent soft-shelled turtles of North America (family + Trionychidae). By Robert G. Webb. Pp. 429-611, pls. 31-54, 24 + figures in text. February 16, 1962. + +Vol. 14. + + 1. Neotropical bats from western México. By Sydney Anderson. + Pp. 1-8. October 24, 1960. + + 2. Geographic variation in the harvest mouse, Reithrodontomys + megalotis, on the central Great Plains and in adjacent + regions. By J. Knox Jones, Jr., and B. Morsaloglu. Pp. 9-27, 1 + figure in text. July 24, 1961. + + 3. Mammals of Mesa Verde National Park, Colorado. By Sydney + Anderson. Pp. 29-67, pls. 1 and 2, 3 figures in text. July 24, + 1961. + + 4. A new subspecies of the black myotis (bat) from eastern + Mexico. By E. Raymond Hall and Ticul Alvarez. Pp. 69-72, 1 + figure in text. December 29, 1961. + + 5. North American yellow bats, "Dasypterus," and a list of the + named kinds of the genus Lasiurus Gray. By E. Raymond Hall and + J. Knox Jones, Jr. Pp. 73-98, 4 figures in text. December 29, + 1961. + + 6. Natural history of the brush mouse (Peromyscus boylii) in + Kansas with description of a new subspecies. By Charles A. + Long. Pp. 99-111, 1 figure in text. December 29, 1961. + + 7. Taxonomic status of some mice of the Peromyscus boylii + group in eastern Mexico, with description of a new subspecies. + By Ticul Alvarez. Pp. 113-120, 1 figure in text. December 29, + 1961. + + 8. A new subspecies of ground squirrel (Spermophilus + spilosoma) from Tamaulipas, Mexico. By Ticul Alvarez. Pp. + 121-124. March 7, 1962. + + 9. Taxonomic status of the free-tailed bat, Tadarida + yucatanica Miller. By J. Knox Jones, Jr., and Ticul Alvarez. + Pp. 125-133, 1 figure in text. March 7, 1962. + + More numbers will appear in volume 14. + +Vol. 15. + + 1. The amphibians and reptiles of Michoacán, México. By + William E. Duellman. Pp. 1-148, pls. 1-6, 11 figures in text. + December 20, 1961. + + 2. Some reptiles and amphibians from Korea. By Robert G. Webb, + J. Knox Jones, Jr., and George W. Byers. Pp. 149-173. January + 31, 1962. + + 3. A new species of frog (Genus Tomodactylus) from western + México. By Robert G. Webb. Pp. 175-181, 1 figure in text. + March 7, 1962. + + More numbers will appear in volume 15. + + + + + +End of the Project Gutenberg EBook of Natural History of the Bell Vireo, +Vireo bellii Audubon, by Jon C. Barlow + +*** END OF THIS PROJECT GUTENBERG EBOOK THE BELL VIREO *** + +***** This file should be named 32855-8.txt or 32855-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/2/8/5/32855/ + +Produced by Chris Curnow, Joseph Cooper and the Online +Distributed Proofreading Team at http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. 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