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We examined geographic patterns of variation and differentiation in morphological characters of the emerald toucanets (Aulacorhynchus spp.) of Mesoamerica. Bill lengths showed flat frequency distributions, suggesting that no “adult” size is reached, and raising the possibility that bill growth in toucanets may be indeterminate. Sparse lowland populations in the Pet;aaen region are of uniformly small body size, suggesting that they may consist of subadult individuals. Patterns of variation support recognition of four species in Mesoamerica: A. wagleri in western Mexico, A. prasinus in eastern Mexico and northern Central America, A. caeruleogularis in Costa Rica and western Panama, and A. cognatus in eastern Panama, as well as several additional forms (A. lautus, A. albivitta, and A. nigrogularis) in South America.
RESUMEN.—Se analizaron los patrones de variacíaon y diferenciación de los caracteres morfológicos en las tucanetas (Aulacorhynchus) de Mesoamérica. La longitud del pico mostró una distribución de frecuencias plana, lo que sugiere la posibilidad de que nunca se alcanza un tamaño “adulto” y, por lo tanto, el crecimiento del pico en las tucanetas es indeterminado. Las escasas poblaciones de las tierras bajas en la región del Petén son uniformemente pequeñas en tamaño corporal, sugiriendo la posibilidad de que estén constituidas por individuos subadultos. Los patrones de variación apoyan el reconocimiento de cuatro especies en Mesoamérica: A. wagleri, del oeste de México, A. prasinus del este de México y norte de Centroamérica, A. caeruleogularis de Costa Rica y el oeste de Panamá, y A. cognatus del este de Panamá, con varias formas adicionales (A. lautus, A. “albivitta” y A. “nigrogularis”) en Sudamérica.
We observed two White-tailed Ptarmigan (Lagopus leucurus) in white winter plumage (basic) in Colorado during late July through August during 35 years of field study. Both individuals were adult (>2 yr of age) females; one was collected and the second examined and photographed. Examination of the plumage revealed that neither had molted from winter plumage into their nuptial (alternate) or postnuptial (supplemental) plumage. We speculate that retention of the white winter plumage was the result of failure of the pituitary and thyroid glands to secrete sufficient hormones to initiate replacement of white body feathers with normal breeding plumage feathers. Perhaps this failure of the pituitary and thyroid glands was not age related but instead gender related. Despite conspicuous white plumage during summer, behavior and survival of both birds appeared normal.
We used morphological measurements and plumage characteristics to identify a Dendroica warbler mist netted and photographed in the Dominican Republic as a possible hybrid between D. kirtlandii (Kirtland's Warbler) and D. fusca (Blackburnian Warbler). We present a detailed description of the individual which is the first presumed hybrid of D. kirtlandii and one of only a few possible hybrids involving D. fusca.
The endangered Kirtland's Warbler (Dendroica kirtlandii) nests primarily in large (>32 ha) stands of young (5- to 25-yr-old) jack pine (Pinus banksiana) which grow on Grayling sand soil. These specific habitat requirements restrict the Kirtland's Warbler breeding range to only 13–16 counties in the northern lower peninsula of Michigan. Although the nature of the species' affinity for this habitat is poorly understood, one theory suggests that higher prey abundance in young jack pine may play a role. To explore further the hypothesis that Kirtland's Warblers choose nesting habitat due to prey abundance, a more thorough knowledge of the warblers' diet is needed. To better understand the diet, we identified arthropod and plant fragments found in 202 Kirtland's Warbler fecal samples, collected from June to September, 1995–1997. The major food items recorded were spittlebugs and aphids (Homoptera; found in 61% of all samples), ants and wasps (Hymenoptera; 45%), blueberry (Vaccinium augustifolium; 42%), beetles (Coleoptera; 25%), and moth larvae (Lepidoptera; 22%).
We studied the lek behavior of the Swallow-tailed Hummingbird (Eupetomena macroura) in an urbanized area in São Paulo state, southeastern Brazil. During the 22-month study we identified a total of 26 lekking territories in one lek that covered an area of approximately 12 ha. The lek was active throughout the year; the number of singing males per morning ranged from 6–15. The abandonment of territories and the establishment of new ones caused continuous rearrangement of lek boundaries. Lekking territories had a mean size of 217 m2 and were separated from each other by 24–120 m. On average, males started singing 27 min before sunrise and kept singing for 17 min. At the end of this period and after a few minutes of silent perching, they abandoned their lekking territories until the next morning. During the singing period, males spent 72–100% of the time inside their territories. The lek behavior of E. macroura is unusual compared to other lekking hummingbirds because of the short daily period of lekking, restricted to just before sunrise. Since males and females of E. macroura possibly defend feeding territories throughout the rest of the day, the short lekking period may represent a tradeoff between two different time budget pressures from lekking and feeding activities.
We describe for the first time the nests of the Wing-banded Wren (Microcerculus bambla), a little-known species of Trogoldytidae from northcentral South America. Two nests were discovered in French Guiana during the rainy season of 1999. Both nests were in abandoned termite mounds attached to the undersides of fallen trees. Chambers of the two nests were lined with a mat of dead leaf fragments. Each nest contained a single, well-feathered nestling that disappeared, possibly due to fledging, within a few days of nest discovery. Although we did not observe nest building, we suspect that other termitaria-nesting birds at our study site, such as Puffbirds (Bucconidae) or Jacamars (Galbulidae) excavated the chambers. Thus, both Microcerculus species with described nests, the Nightingale Wren (M. marginatus) and the Wing-banded Wren, apparently are secondary cavity nesters.
I investigated the relationship between the physical characteristics of breeding territories and the reproductive success of Black Oystercatchers (Haematopus bachmani) in British Columbia. I compared measures of the threat of egg and brood depredation, conspecific competition, and food supply with measures of reproductive success on 38 oystercatcher breeding territories during 1996 and 1997. Oystercatchers breeding on territories near Glaucous-winged Gull (Larus glaucescens) colonies had smaller first clutches than pairs free of neighboring gulls. Oystercatcher pairs hatched and consequently produced more young on shallow sloping intertidal shoreline sites compared to steep-sloped islets and shorelines.
Despite conservation concern for the Swainson's Warbler (Limnothlypis swainsonii), little is known about its nonbreeding ecology. Because body condition can provide an indication of habitat quality, we examined Swainson's Warbler body condition indices in dry limestone forest and second growth scrub habitats in Jamaica, where this species was relatively common. In dry limestone forests, Swainson's Warblers showed no seasonal change in body mass corrected for structural size, furcular fat score, or age ratio. This contrasts with results from studies of other species of Neotropical migrant warblers that showed significant seasonal declines in body mass in similar xeric habitats. Dry limestone forest sites also supported a greater and less spatially variable biomass of prey commonly consumed by Swainson's Warblers than second growth scrub and shade coffee. Because Swainson's Warblers consume prey concealed beneath the leaf litter surface, they apparently are less susceptible to the extreme dry season desiccation that affects the availability of arthropods on the leaf litter surface and in the forest canopy. Swainson's Warbler density (0.6 birds/ha) and overwinter persistence (52%) also were relatively high in dry limestone forest sites, suggesting these forests provide high quality winter habitat for this species. Although Swainson's Warblers were able to increase body mass in preparation for migration in one second growth site, these disturbed habitats may vary in quality for Swainson's Warblers. Our results highlight the need for conservation of dry forests in the Greater Antilles as nonbreeding habitat for the Swainson's Warbler, as well as for numerous endemic species dependent upon these forests.
Many avian species have demonstrated differential wintering of the sexes, either latitudinally across their wintering range or by habitat. We examined the large numbers of wintering Ruby-crowned Kinglets (Regulus calendula) captured as part of a long term constant effort mist-netting program in coastal California to determine if such a pattern was evident in this population. Data from 1976 to 1997 revealed a consistent and significant female bias, with a mean of 2.13 (± 0.31 SE) females caught per male. We evaluated the possibility that this bias resulted from differential capture probabilities of the sexes, and found no difference in recapture probabilities between males and females. The sex ratio was biased toward females in both scrub and mixed evergreen forest habitats, but significantly more skewed in the former (3.68:1 versus 1.91:1). We also examined captures over a two-year period from nearby stations in riparian forest; the sex ratio was least skewed in this habitat (1.37:1). Considered together with the latitudinal differential distribution of this species observed in eastern and central North America, our data suggest that Ruby-crowned Kinglets may not only be geographically but also ecologically segregated according to sex across their wintering range.
We describe vocalizations of Ruby-throated Hummingbirds (Archilochus colubris) recorded during agonistic confrontations at feeders. Calls were composed of 1–5 different note types. A sixth distinct note type, the W note, was not given within a call sequence. Similar to those of Black-chinned Hummingbirds (Archilochus alexandri), Ruby-throated Hummingbird calls were complex, and exhibited a nonrandom organizational pattern as analyzed using a Markov model. The two closely related yet allopatric species shared similarities in the acoustic structure of note types, syntax, and call length. Slight differences occurred in the opening note types of calls in the two species. We investigated how vocalizing is associated with the outcome of encounters at a feeder and found that the vocalizer usually was the winner.
Microgeographic variation in song is a well-documented consequence of song learning in many songbirds, but the relationship between song variation and development in the suboscines is poorly understood. Because learning appears to play a role in song development in Long-tailed Manakins (Chiroxiphia linearis), we wanted to find out whether they also exhibit microgeographic variation in song. We compared songs of Long-tailed Manakins from three localities in Costa Rica using multivariate analysis of variance and canonical discriminant analysis of five song variables. Differences among localities were not significant, and songs from the same localities did not cluster together in a canonical plot. This finding is similar to those observed in suboscine flycatchers whose songs are innate.
We document characteristics of the previously undescribed nest, nest site, and eggs of the Ochre-breasted Antpitta (Grallaricula flavirostris). We found three nests in 1999 and 2000 in the Talamanca Mountains of southern Costa Rica. The nests were cup shaped and constructed primarily of green moss with linings of thin sticks and black rhizomorphs. Mean nest height above the ground was 3.1 m. Nests were located in the forks of slim saplings in two cases and, in one case, in a larger tree at a point where several smaller branches left the trunk. We observed clutches of one and two eggs. Eggs appeared pale reddish brown with some darker spotting. The incubation period was 17–21 d and we estimate the nestling period lasts 14–16 d.
Reproduction among close relatives is rare in birds. Here we report two cases of pair formation between mothers and sons in a marked population of Common Loons (Gavia immer) in northern Wisconsin, one of which resulted in the fledging of a chick. Short distance natal dispersal by males coupled with short distance breeding dispersal by adults after territorial displacement sets the stage for occasional mother-son pairings in this species, although data from multilocus DNA fingerprints indicate that such pairings are infrequent.
We report on the incidence of male incubation and multiple brooding in Sagebrush Brewer's Sparrows (Spizella breweri breweri) at the northwestern limit of their breeding range in southern British Columbia, 1998–2000, and in central Washington, 1996–1999. Males frequently incubated eggs, accounting for 28% of 329 observations of incubation by known individuals in British Columbia. In Washington, 51% of the males we monitored incubated eggs. Males and females appeared equally able to increase nest temperature. In British Columbia, 17% of females fledged two broods per season, and two females fledged three broods. In Washington, 5% of males fledged two broods per season. Only one previous case of male incubation has been reported in this species and multiple brooding has been poorly documented. These aspects of the breeding biology of other well-studied species may be underestimated without the careful examination of populations of marked individuals.
We measured the occurrence, size, and composition of Razorbill (Alca torda) nest structures at the Gannet Islands, Labrador, Canada. More Razorbill pairs nested in enclosed crevices than on open-topped ledges, and in both habitats the majority laid their single eggs on nest structures built at the breeding site (70% overall). Most nests were composed entirely of pebbles, but many also had vegetation in the structure. On average, Razorbill nest structures included about 40 pebbles and weighed 100–150 g. These nest structures probably serve two main functions: first, they reduce the risk of accidental egg loss, and second, they allow water to drain from under the egg, keeping it dry. We conclude that Razorbills have a strong nest-building tendency, a drive that often has been overlooked.
We observed a male Razorbill (Alca torda) residing among a group of breeding Common Murres (Uria aalge) on Great Island, Newfoundland, during 1996–2000. Behavioral observations indicated that the presence of the Razorbill directly contributed to the break-up of one pair of murres and prevented another pair from producing an egg. In addition, murres with sites close to the Razorbill site may have experienced increased energetic demands arising from aggressive interactions frequently initiated by the Razorbill. A consequence of the presence of a heterospecific resident in a seabird colony may be decreased reproductive success for individuals breeding nearby.
The exotic tree, Russian olive (Elaeagnus angustifolia), has invaded riparian zones throughout much of the western Unites States. Although promoted as a useful species for wildlife because of its abundant edible fruit, evidence for its value to breeding birds remains sparse. We compared relative rates of usage, nest success, and cowbird parasitism of birds breeding in Russian olive versus native tree species at a site where Russian olive is a minor component. Some species, such as the Mourning Dove (Zenaida macroura) and Yellow-breasted Chat (Icteria virens), preferentially placed their nests in Russian olive. Nest success was similar for nests in Russian olive and native species. During 1997, nests of the Willow Flycatcher (Empidonax traillii) were significantly more likely to be parasitized by Brown-headed Cowbirds (Molothrus ater) when placed in Russian olive than in native species, although nest success was not significantly different. Our results may not apply to areas where Russian olive is common.
Using video to study nest predation at Fort Hood, Texas, we documented female Brown-headed Cowbirds (Molothrus ater) removing nestlings at 7 of 133 (5.3%) Black-capped Vireo (Vireo atricapillus) and 1 of 11 (9.1%) Golden-cheeked Warbler (Dendroica chrysoparia) nests. It has been suggested that female cowbirds depredate nests they find late in the host's nesting cycle to stimulate renesting by hosts, thereby enhancing future opportunities for parasitism. At Fort Hood, the function of nestling removal by cowbirds is unclear, because cowbirds caused nest failure during only two of eight visits. At three nests, we also observed cowbirds ingesting or removing fecal sacs produced by host nestlings. Fecal sac ingestion by cowbirds, though apparently infrequent, may provide a nutritional benefit.
Information is lacking on predation of adult Golden-cheeked Warblers (Dendroica chrysoparia). Using time lapse video equipment at Fort Hood, Texas, I documented a Great Plains rat snake (Elaphe guttata emoryi) depredating a female Golden-cheeked Warbler on a nest. The predation took place on the night of 22–23 April 2000 while the adult warbler was sleeping on four eggs. Although adult mortality by predators probably occurs infrequently, the climbing ability and nocturnal foraging of rat snakes may enhance opportunities of capturing adult birds.
We observed apparent cooperative hunting by a pair of Loggerhead Shrikes (Lanius ludovicianus) in eastern Oregon, USA. A western terrestrial garter snake (Thamnophis elegans) was killed by the shrikes and then transported by one to an unknown location. The snake was carried in the direction of an active nest that was 90 m from the location where the snake was killed. This is the first time that apparent cooperative hunting has been documented in the genus Lanius.