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We documented the time of day of laying and the total time spent on the nest during laying (laying bout) in 21 species of passerine birds and the brood-parasitic Brown-headed Cowbird (Molothrus ater) at Delta Marsh, Manitoba, between 1989 and 1995. Brown-headed Cowbirds laid on average 31.2 min before sunrise, whereas mean laying times of the other species ranged from 11.3 min after sunrise through early afternoon. Species that laid later in the day tended to spend more time on their nests during laying. Smaller species tended to lay earlier in the day and had significantly shorter laying bouts than larger species. Future studies accounting for variation in foraging and reproductive behavior and predation risk between taxonomic groups may explain additional variation in laying time and duration.
We compared 50-m fixed-radius point-count detections for four bird species with density data from spot-mapping in order to evaluate the relationship between monitoring methodologies. We conducted this study in five Missouri oak-hickory forest study sites over eight years. There were significant positive correlations between monitoring methods, but the strength of these relationships varied for Acadian Flycatchers (Empidonax virescens), Ovenbirds (Seiurus aurocapilla), Worm-eating Warblers (Helmitheros vermivorus), and Wood Thrushes (Hylocichla mustelina). There was significant bias associated with the point-count detections for Acadian Flycatchers, Worm-eating Warblers, and Wood Thrushes. The direction and degree of bias varied; for example, Acadian Flycatchers and Worm-eating Warblers were on average significantly overestimated by point counts, whereas the Wood Thrush was significantly underestimated and Ovenbirds were slightly underestimated. The magnitude and direction of the bias error varied with spot-map density estimates of the species, but was not related to specific study sites or years. Thus 50-m radius fixed-radius point counts appear to reflect general density trends for the four species, especially for Ovenbirds, but there are also density related biases associated with point-count detections.
We monitored a marked Pacific Golden-Plover (Pluvialis fulva) over many seasons on a wintering ground in Hawaii. The bird died at a minimum age of 21 yr 3 mo, thus demonstrating the potential for a long lifespan in some individuals and setting a new longevity record for the species.
Data from a banding station at Guantanamo Bay and the examination of 830 specimens were used to study molt patterns and criteria for determination of age and sex in 15 resident species of Cuban landbirds. All 15 species undergo their prebasic molt in August to November, with a few species commencing as early as May and/or completing as late as December. This timing corresponded with that of related taxa found in North America. With few exceptions, the extent of the first prebasic molts was also comparable to those of related taxa found at northern latitudes, being partial to incomplete in all nine passerines and four of six nonpasserines. Three species showed evidence of eccentric primary molt patterns during the first prebasic molt, to be expected in birds residing in scrubby or exposed environments such as those found at Guantanamo Bay. Determination of age is possible in most Cuban landbirds based on molt limits and the shape and condition of the primary coverts and rectrices, criteria very similar to those found in North American species of related taxa.
Song variation has been studied extensively over the past 50 yr but almost entirely in oscine passerines. Although learning is an essential component of song development in most, if not all, oscines, there is no definitive evidence for song learning in suboscine passerines. This suggests that the patterns and extent of individual and geographic variation may differ between these groups as well. We examined individual variation in the “fee-bee-o” song in a population of Alder Flycatchers (Empidonax alnorum) in southwestern Alberta. Songs of individual males were recorded during the breeding season in 2001. We measured temporal and frequency variables of songs and conducted univariate and multivariate statistical analyses to characterize variation within and among individuals. There was little variation among the songs of an individual male during single recording sessions and across recordings made over the breeding season. All measured variables varied significantly more among than within individuals. Discriminant function analysis assigned 91–100% of songs to the correct individual. Therefore, there was sufficient variation among individual males to identify them statistically and, potentially, to permit individual discrimination by the birds.
We determined if extra-pair paternity existed in an eastern population of Song Sparrows (Melospiza melodia melodia), and compared the frequency of extra-pair paternity in first and second broods. Over both broods, a total of 10.5% young were of extra-pair origin, but this frequency is considered conservative as it was based on only three loci. Forty percent of females had extra-pair young in at least one of their two broods. One of five females changed from genetic monogamy to genetic promiscuity between broods, despite remaining paired with the same male. Studies of double-brooded species are ideal for examining factors other than mate quality that might influence rates of extra-pair paternity.
Shorebirds held during banding activities can develop muscle cramps, especially when temperatures are high and birds are heavy. Such capture myopathy can be fatal or render birds vulnerable to predators. We rehabilitated Great Knots (Calidris tenuirostris), Red Knots (C. canutus), Bar-tailed Godwits (Limosa lapponica), and Red-necked Stints (C. ruficollis) in northwestern Australia. We kept birds in slings (if cramped) or in a small cage (if able to walk) and gave them daily standing exercises. Recovery of severely cramped birds took up to 14 d, which may reflect a critical period of tissue regeneration. Of 15 knots (8 Red and 7 Great) taken into captivity, 12 were rehabilitated and released. The resighting rate after the breeding season of the rehabilitated birds was the same as for other birds color-banded during our research, indicating that the rehabilitation was successful. We conclude that rehabilitating cramped shorebirds is possible though time-consuming. A sex bias in susceptibility to capture myopathy is suggested by seven of the eight Red Knots treated being male; the sex ratio in the local population was 1:1.
Brown-headed Cowbird (Molothrus ater) parasitism on pewees (Contopus spp.) is uncommon or rare in North America, suggesting that pewees sympatric with cowbirds either reject cowbird eggs or are not selected by cowbirds for parasitism, or that cowbirds are unable to parasitize pewee nests. At Delta Marsh, Manitoba, we inspected Eastern Wood-Pewee (C. virens) nests to determine parasitism frequency and experimentally parasitized pewee nests with real and artificial Brown-headed Cowbird eggs to assess their response to parasitism. No parasitism was recorded at 20 unmanipulated nests or at 12 experimentally parasitized nests, whereas all real and artificial cowbird eggs were accepted. The lack of observed parasitism, therefore, was not an artifact of cowbird egg rejection. We suggest the lack of parasitism on Eastern Wood-Pewees at Delta Marsh reflects a partial asynchrony between the parasite's and host's laying seasons and possibly the high placement of pewee nests. However, these factors may not explain the lack of parasitism at all other sites in North America or on other Contopus species.
The double observer approach with marked nests was used in southern France for estimating the detection probability of nests of the Squacco Heron (Ardeola ralloides), a cryptic species in its breeding behavior. Results indicate that the detection probability varied from 0.518 to 0.700 between observers. The overall detection probability, i.e., the probability that a nest was detected by at least one observer, was 0.856. Given a total of 66 nests found by both observers during the surveys, the breeding population was estimated at 77 nests. Since previous estimates of the Squacco Heron breeding population size did not take into account detection probability, we suggest that the breeding population is larger than previously thought in the Camargue and in other European breeding localities.
We conducted a short-term study on density and habitat use in an Amazonian owl assemblage. The census was conducted in terra-firme forest and black-water flooded forest or igapó forest. Six owl species were recorded, the Tropical Screech-owl (Otus choliba), the Tawny-bellied Owl (O. watsonii), the Black-banded Owl (Strix huhula), the Spectacled Owl (Pulsatrix perspicillata), the Ferruginous Pygmy-owl (Glaucidium brasilianum), and the Stygian Owl (Asio stygius). The most abundant species was the Tawny-bellied Owl (0.42 individuals/ha) followed by the Spectacled Owl (0.31 individuals/ha). Some species showed clear tendencies to use different habitats. The Tawny-bellied Owl was more abundant in terra-firme forest, while its congener, the Tropical Screech-owl, was much more common in igapó forest. The Stygian Owl and the Ferruginous Pygmy-owl were also recorded exclusively in the igapó forest census. These results indicate that terra-firme forest and igapó forest supported distinct owl assemblages. Our work and other studies suggest regional variability in owl density in Amazonia.
We used differential counts of white blood cells to determine heterophil:lymphocyte ratios in the Maui Creeper (Paroreomyza montana), an endemic, non-endangered Hawaiian honeycreeper, as a measure of stress in response to varying distance and handling technique during translocations. The Maui Creeper was used as an in situ experimental model for the Po'ouli (Melamprosops phaeosoma), an endangered species for whom translocation is critical for its recovery. We translocated 18 Maui Creepers across rugged terrain by hand-carrying individual birds for two distances (1.0 or 2.5 km) inside portable containers. We tested two methods of confinement that varied in the degree of physical restraint during translocation. Birds translocated across longer distances developed significantly higher heterophil:lymphocyte ratios than those moved shorter distances. However, no significant difference was seen between container types. Our findings build on a previous study of stress response in passerines, and indicate that using heterophil:lymphocyte ratios to measure stress may be a valuable tool for evaluating management practices for other critically endangered passerines.
Cover at nesting sites selected by breeding birds can reduce the risk of nest predation. Using artificial nests, we tested whether dense cover reduces nest predation upon understory birds (rhinocryptids) in temperate forest of Chile. We compared nest predation for artificial nests placed under a dense thicket, nests placed with no cover, and nests located randomly regarding available cover. Contrary to predictions, we found no differences in nest predation probabilities for the three covered nest-site treatments. Cover at nesting sites is not an effective anti-predator mechanism as the main predators, generalist small mammals, also prefer the same sites.
A male Flammulated Owl (Otus flammeolus), banded as a breeding adult (age unknown) on 8 July 1988 in central Colorado, was last recaptured on 8 July 2001. On the same study area, a female Flammulated Owl was banded as a breeding adult (age unknown) on 7 July 1988 and was last recaptured on 22 June 1995. These data establish longevity at a minimum 14 yrs for males and 8 yrs for females. The data suggest that Flammulated Owls may be relatively long-lived, and support evidence that this species has a life history strategy similar to larger raptors.
We reconstructed the nutrient source for egg synthesis by sampling Black-headed Gull (Larus ridibundus) eggs for yolk, analyzing their carbon stable isotope ratio, and comparing that to hatchling down. Most of the variation in carbon stable isotope ratio was explained by differences between nests, the within-nest variation being explained by laying order. These data indicate significant differences in diet choice between individual females and changes in food choice or body-store dynamics during egg laying. Among-egg variation in the carbon stable isotope ratios of the yolk were closely reflected in the hatchling down, on average down being enriched by 3.1‰ δ13C relative to yolk. Our findings support the contention that pre-laying female diets can be evaluated from hatchling down.
Although predator model presentations are frequently used by ornithologists to study parental care, little is known about the effects of presentations on subsequent nesting success. Only one of 113 model presentation studies surveyed from the literature examined the influence of such experiments on nesting success, and this was conducted with Tree Swallows (Tachycineta bicolor), a cavity-nesting species. I conducted a field test to determine whether model presentations affected fledging success of an open-cup nesting species, the Hooded Warbler (Wilsonia citrina). In 1999, I presented predator models at the nests of Hooded Warblers at the Hemlock Hill Biological Research Area in northwestern Pennsylvania. I compared the fledging success of this species in 1999 with fledging success in the four previous years at the same study site when no such tests took place. Predator model presentations during the nestling stage had no effect on fledging success of this species.