Beak abnormalities are rare among adult birds and, typically, are not widespread in a given population, within a region, or across multiple species. A high concentration of beak deformities was recently documented in Black-capped Chickadees (Poecile atricapillus) and other resident avian species in Alaska. We describe a parallel condition in Northwestern Crows (Corvus caurinus) that signals the emergence of a multispecies epizootic. On the basis of 186 Northwestern Crows captured at six sites in Alaska during 2007 and 2008, we estimated the prevalence of beak deformities in adults to be 16.9 ± 5.3%, the highest rate of gross deformities ever recorded in a wild bird population. Prevalence varied among sites and was as high as 36% on the Kenai Peninsula, which suggests possible epizootic clusters. We also documented beak abnormalities in an additional 148 Northwestern Crows in south-central and southeastern Alaska and in 64 crows near Vancouver, British Columbia, and Puget Sound, Washington, a region where both Northwestern Crows and American Crows (C. brachyrhynchos) occur. The increase in frequency and distribution of crows observed with abnormal beaks throughout the Pacific Northwest since the late 1990s indicates a geographic expansion of this problem. Affected crows exhibited elongated and often crossed beaks that were morphologically similar to deformities documented in Black-capped Chickadees and other species in Alaska over approximately the same period. Additional research is needed to determine the etiology and potential adverse effects on bird populations affected by this disorder.

Variation in the appearance of eggs within a clutch has been hypothesized to decrease the likelihood of rejection of brood-parasite eggs, but tests of the hypothesis have produced mixed results among cuckoo (Cuculus canoras and Clamator glandarius) hosts. The hypothesis has not been tested in cowbird hosts because they typically show little intraspecific variation in responses to cowbird eggs. However, the Common Grackle (Quiscalus quiscula) is unusual among potential hosts of the Brown-headed Cowbird (Molothrus ater) because it shows both acceptance and rejection of cowbird eggs and it demonstrates high intraclutch variation in egg appearance, which makes it one of the few potential cowbird hosts suitable for a test of the intraclutch variation—host rejection hypothesis. We tested whether intraclutch variation in the appearance of Common Grackle eggs influenced the likelihood of egg rejection and found that Common Grackles with greater variation in intraclutch egg appearance were more likely to accept cowbird eggs when these were added prior to clutch completion. These results are the first to indicate that even when a host has eggs that are dramatically different from those of a parasite, variation in its own eggs may increase the threshold required to elicit egg rejection.

Several hypotheses have been proposed to explain the evolution of conspecific brood parasitism (CBP), and recent studies suggest that nest predation may be an important factor in shaping this behavior. We assessed whether individuals that engage in parasitic laying preferentially deposit their eggs in safe nest sites (i.e., risk assessment hypothesis). We tested the predictions of this hypothesis using a population of Common Eiders (Somateria mollissima dresseri) nesting at Table Bay, Labrador, Canada, in 2007. Common Eiders at this location nest in three habitats (dense woody vegetation, open grassy vegetation, and nest shelters) that vary in their exposure to avian predators. We used isoelectric focusing electrophoresis of egg albumen to quantify the frequency and distribution of CBP among habitats. Nest-site safety did not explain patterns of CBP among habitats, given that nests in dense woody vegetation had the highest probability of survival (0.70; 95% confidence interval [CI]: 0.50–0.89) yet had the lowest frequency of CBP (33%). There was also no indication that parasitized and nonparasitized nests differed in their probability of nest survival (0.65 [95% CI: 0.41–0.83] vs. 0.58 [95% CI: 0.33–0.80]). We propose explanations for why our data did not support the risk assessment hypothesis.

Migratory birds are known to be able to navigate—to determine their position on the globe and the direction toward their distant goal—even if they cannot perceive any information emanating from the goal. One hypothesis, that of true bicoordinate navigation, claims that birds should be able to sense and use a grid of two natural parameters as coordinates. Some indirect data support the idea that migratory birds can determine their north—south position, and several recent studies have suggested that at least longdistance migrants, including the Eurasian Reed Warbler (Acrocephalus scirpaceus), can determine their east-west position. How they do this remains a mystery. Birds could theoretically detect the magnitude of east-west displacements if they have two clocks, one synchronizing faster to local time than the other. We tested whether this putative “double-clock” mechanism may serve as a navigational tool for detecting east-west position. We captured Eurasian Reed Warblers during spring migration and tested their orientation in Emlen funnels under capture-site photoperiodic conditions. After these northeasterly oriented control tests, we exposed them to a light—dark regime that simulated a 1,000-km eastward displacement to the Moscow region from which we have shown that actually displaced Eurasian Reed Warblers on spring migration compensate for their displacement by orienting northwestwardly. Exposure to the Moscow light-dark regime did not affect the birds' orientation. Our results suggest that light-dark regime effects alone are unlikely to trigger compensation for the longitudinal displacement in long-distance migratory Eurasian Reed Warblers.

The preferences that bird species exhibit for different sugar types may play a role in pollinator-mediated selection on plant nectar composition. How bird sugar-type preferences are affected by concentration is a fundamental question for research that aims to use those preferences to explain plant nectar composition. Such research has been done for several specialist avian nectarivores, and for a few passerine occasional nectarivores, but not, apparently, for any nonpasserine occasional nectarivore. We examined the effect of concentration of sugar solutions on sugar-type preferences of the Speckled Mousebird (Colius striatus), a common African nonpasserine that occasionally feeds on floral nectar. Surprisingly, the species exhibited a concentration-dependent switch in sugar preference, from hexose sugars at low concentration to sucrose at high concentrations, that was remarkably similar to that shown by specialist avian nectarivores and that contrasts with results reported for passerine occasional nectarivores. During these experiments, Speckled Mousebirds were unable to meet energy demands on low-concentration diets and lost significant body mass when fed 5% and 10% solutions. The birds showed no preference among four different hexose solutions representing the range of concentrations (10–25%) found in bird-pollinated flowers, and there was no difference in their ability to digest sucrose and hexose sugars. Our results suggest that Speckled Mousebirds have sugar-preference traits that are similar to those of specialist avian nectarivores, whereas their apparent lack of concentration preference is similar to that found in passerine occasional nectarivores.

Studies on the sonations (nonvocal communicative sounds) of birds have revealed a wide diversity of mechanisms and functions. We describe the kinematics and sounds of the display dive and shuttle display of the male Black-chinned Hummingbird (Archilochus alexandri). Males produced an integrated series of trilled and tonal sounds during their displays. Through a combination of experiments on wild birds, experiments on isolated feathers in the laboratory, and comparisons between high-speed video and audio recordings, we show that the display sounds are sonations produced by feathers. The timing of the trilled sounds during both the shuttle and dive displays corresponded to the wingbeat kinematics, which suggests that they are produced by the wings. These trills were qualitatively similar to the wing trills reported for other species of hummingbirds, but the mechanism of sound production remains unclear. The production of the tonal sounds during the display dive corresponded to tail spreads, and experiments show that this sound was produced by fluttering of the tip of the outer tail feather, rectrix 5 (R5). Hummingbirds in the genus Calypte also produce dive sounds with R5, but sound is instead generated by the trailing vane of the feather. Calypte and Black-chinned Hummingbirds differ in the shape of the tip of R5, and we hypothesize that this difference in shape affects which mode of flutter is activated by airflow.

Previous microsatellite analysis (Barr et al. 2008) of the endangered Black-capped Vireo (Vireo atricapilla) revealed a low (F_ST = 0.021) but statistically significant level of population differentiation with isolation by distance (IBD); most pairwise F_ST values among populations were significant. No clear geographic pattern was detected, although populations in Oklahoma were somewhat differentiated, as expected from the observed pattern of IBD. Because nuclear loci, including microsatellites, coalesce more slowly than mtDNA, we sequenced the mitochondrial ND2 gene for 108 individuals sampled from breeding populations in Oklahoma, Texas, and Mexico to determine whether there was a clearer geographic pattern than that resolved by the microsatellite allele-frequency data. We obtained an F_ST value of 0.024 (P = 0.08), confirmed IBD, but also did not detect geographic structuring in the haplotype network. The authors of the microsatellite study suggested that the significant F_ST value indicated that populations were not currently connected by gene flow and that the greater attention should be given to dispersal behavior when considering the species' population dynamics. We suggest that the unstructured haplotype network reveals that the Black-capped Vireo can be managed without regard for genetic distinctiveness. That is, we contend that statistical significance of the microsatellite F_ST value has been inappropriately equated with biological significance. We believe that a gene-tree approach, emphasizing reciprocal monophyly, is more appropriate when assessing genetic subdivisions in a species that might then merit special conservation concern.

The taxonomic identity of endangered populations of the Least Tern (Sternula antillarum) has long been debated. Their current conservation status provides even more impetus to examine the taxonomic distinctness of these groups. We used rapidly evolving mitochondrial DNA control-region sequences (840 base pairs; n = 188) and microsatellite DNA data (7 loci; n = 417) to examine genetic structure within and among three subspecies that occur within the United States: California Least Tern (S. a. browni), Interior Least Tern (S. a. athalassos), and Eastern Least Tern (S. a. antillarum). Although significant genetic structure was observed among breeding populations from across the species' range, our data indicated little evidence of genetic structure within traditional subspecific groups. Isolation-by-distance analyses, however, identified subtle patterns that may reflect sex-specific differences in dispersal behavior. Our analyses likewise demonstrated little population subdivision among subspecific groups, which raises questions regarding the taxonomic status of traditionally defined subspecies. Our findings can therefore be used to consider a reevaluation of Least Tern subspecies by the American Ornithologists' Union's Committee on Taxonomy and Nomenclature. We further emphasize the need for studies of range-wide breeding-site fidelity and natal philopatry to better understand interpopulation movements of individuals throughout the annual cycle.

Bile salts are the major end-metabolites of cholesterol and are important in lipid digestion and shaping of the gut microflora. There have been limited studies of bile-salt variation in birds. The purpose of our study was to determine bile-salt variation among bird taxa and relate this variation to current avian phylogenies and hypotheses on the evolution of bile-salt pathways. We determined the biliary bile-salt composition of 405 phylogenetically diverse bird species, including 7 paleognath species. Bile-salt profiles were generally stable within bird families. Complex bile-salt profiles were more common in omnivores and herbivores than in carnivores. The structural variation of bile salts in birds is extensive and comparable to that seen in surveys of bile salts in reptiles and mammals. Birds produce many of the bile salts found throughout nonavian vertebrates and some previously uncharacterized bile salts. One difference between birds and other vertebrates is extensive hydroxylation of carbon-16 of bile salts in bird species. Comparison of our data set of bird bile salts with that of other vertebrates, especially reptiles, allowed us to infer evolutionary changes in the bile-salt synthetic pathway.

The Eurasian Bullfinch (Pyrrhula pyrrhula) is unusual among passerines in that it has both an extremely unusual sperm morphology and unusually high levels of inter- and intra-male variation in sperm morphology. One possible cause of this high level of variation in sperm design is the phenotypic results of inbreeding following a bottleneck event. There are two points in time when the Eurasian Bullfinch may have been subject to a bottleneck. Many Eurasian passerines underwent a series of post-Pleistocene bottlenecks following the retreat of the glaciers. More recently, in the United Kingdom the Eurasian Bullfinch has declined severely in numbers in the past 40 years. We used universal bird microsatellite primers to directly compare the genetic diversity of the Eurasian Bullfinch with that of three fringillid finch species that display “typical” passerine sperm morphology: the European Greenfinch (Carduelis chloris), Common Chaffinch (Fringilla coelebs), and Red Crossbill (Loxia curvirostra). We found no evidence that the Eurasian Bullfinch has undergone a reduction in genetic variation that could account for its unusual sperm morphology. Alternative hypotheses, such as a relaxation in sperm competition, now warrant further investigation.

Multiple-observer point-count methods allow estimation of detection probability and have some advantages over other point-count methods. We introduce the unreconciled double-observer method, an independent double-observer method that does not require observers to match or otherwise reconcile individual observations. The modeling of the counts uses the repeated-counts model (Royle 2004). We compared estimates of detection probability and abundance from the unreconciled double-observer method with estimates from the traditional independent double-observer method (which requires matching of individual animals) using field-simulated bird-point-count data. The unreconciled double-observer method provided point estimates of detection probability and abundance that were essentially identical to the results of the independent double-observer method, even though much less effort was required to collect data with the unreconciled method. Estimates of detection probability from the unreconciled double-observer method were usually less precise—and estimates of abundance always less precise—than those from the independent double-observer method, because there is less information available in the unreconciled double-observer approach. We also evaluated the unreconciled double-observer method on 12 Breeding Bird Survey (BBS) routes. The unreconciled double-observer method provided estimates of route-level abundance for most routes and for most of the 20 species we considered. We believe that this method has potential for established bird-monitoring programs such as the BBS because no changes in historical data-collection methods are required other than collecting data simultaneously using two or more observers.

Many songbirds are seasonally frugivorous and eat primarily fruit during migration and insects or seeds during nonmigratory periods. Previous work has suggested that most wild fruits may have inadequate protein for birds. Assessing the nutritional adequacy of fruit requires knowing the protein requirements of birds in relation to the composition of available fruits. We tested predictions of two hypotheses: (1) interspecific differences in protein requirements of birds are related to their foraging strategy; and (2) protein requirements of birds increase with demand, for example during migratory periods of the annual cycle. We measured the protein requirements of the omnivorous Hermit Thrush (Catharus guttatus) and the granivorous White-throated Sparrow (Zonotrichia albicollis) during nonmigratory and migratory stages of the annual cycle and compared the results with published estimates for other songbird species. In the nonmigratory state both species ate less, lost body mass, and had more negative nitrogen balance as dietary protein decreased. In the migratory state Hermit Thrushes lost body mass and had lower nitrogen balance but did not reduce food intake as dietary protein decreased, whereas White-throated Sparrows did not change body mass, food intake, or nitrogen balance as dietary protein decreased. Both species had lower protein requirements during migration (9.3 mg N day^-1 and 15.8 mg N day¹, respectively) than during nonmigratory periods (53.1 mg N day^-1 and 46.0 mg N day^-1, respectively) when fed a diet containing 15.9 kJ g^-1. These findings may partially explain how birds can adequately refuel on protein-limited foods such as fruits during migration.

Recent research has confirmed the efficacy of migration monitoring to estimate trends in the populations of raptors sampled at traditional watch-sites. We used autumn satellite tracks of 57 adult Ospreys (Pandion haliaetus) captured on the breeding range in North America between 1995 and 2000 to assess the extent to which migration monitoring sampled their populations. We used (1) 3-km-wide and 6-km-wide linear trajectories (migration paths) that connected locations with straight lines and (2) utilization distributions derived from Brownian bridge movement models to estimate the proportions of Ospreys likely to have been detected by watch-sites and watch-sites likely to have detected tagged birds, and to describe the geography of southward migration between North America and South America. The migration path method estimated continental detection rates of 12–23%, with regional maxima of 21–36% in eastern North America. This analysis indicated that 8–20% of all watch-sites could have detected ≥1 of the satellite-tracked Ospreys. The Brownian bridge method estimated that 95% of the utilization distributions of migrating Ospreys in North America intersected ≥1 watch-site and that 89% of all watch-sites intersected ≥1 utilization distribution. Using this method, regional probabilities of detection (mean ± SD) for individuals were estimated to be 33.8 ± 28.8% in eastern, 5.8 ± 6.6% in midwestern, and 4.7 ± 4.9% in northwestern (Pacific coast) North America. Migrating Ospreys appear to concentrate along well-defined, narrow fronts and to use land bridges where available, rather than travel along broad fronts and engage in large water crossings during autumn migration.

Streaked Shearwaters (Calonectris leucomelas) breed in temperate regions of East and Southeast Asia and have been thought to migrate to tropical regions near the Equator after breeding. We documented the migratory and foraging behavior of this species using global location sensors (GLS). The GLS loggers were attached to 48 breeding birds in 2006 and were subsequently recovered from 38 birds in the following year. The Streaked Shearwaters migrated from the seas around Japan to three wintering areas in the tropics, the seas off northern New Guinea, the Arafura Sea, and the South China Sea (4,000, 5,400, and 3,500 km from the breeding colony, respectively). Most Streaked Shearwaters wintered off northern New Guinea, an area of low primary productivity but high Skipjack Tuna (Katsuwonus pelamis) abundance. Streaked Shearwaters flew for longer periods and landed on the water more frequently around dawn and dusk during the wintering period. This pattern of activity is similar to that of subsurface predators such as tuna, and to that of tropical seabirds that are known to feed with subsurface predators. We suggest that Streaked Shearwaters probably forage in association with subsurface predators in the tropical oceans during the wintering period. Foraging in association with subsurface predators and morphological adaptations for gliding may allow Streaked Shearwaters to forage efficiently in both temperate and tropical environments.

The sudden appearance of a large cluster of animals with gross abnormalities may signal a significant change in an ecosystem. We describe an unusual concentration of beak deformities that appear to have arisen rapidly within Alaska and now extend southward along the Pacific Coast. In Alaska we have documented 2,160 Black-capped Chickadees (Poecile atricapillus) and 435 individuals of 29 other species of birds, primarily during the past decade, with grossly overgrown and often crossed beaks. The annual prevalence of beak abnormalities among adult Black-capped Chickadees in south-central Alaska varied from 3.6% to 9.7% and averaged 6.5 ± 0.5% between 1999 and 2008. Only 0.05 ± 0.05% of nestlings and 0.3 ± 0.2% of juveniles <6 months old had abnormal beaks, which suggests that this is either a latent developmental or an acquired condition. We documented 80 cases in which a Black-capped Chickadee captured with an apparently normal beak was subsequently recaptured with a beak abnormality and 8 cases in which a beak deformity was no longer detectable upon recapture. Necropsy and histopathology of a sample of affected individuals provided no conclusive evidence of the etiology of this condition. Deformities appear to affect primarily the keratin layer of the beak and may result from abnormally rapid growth of the rhamphotheca. Some affected birds also exhibited lesions in other keratinized tissues of the skin, legs, feet, claws, and feathers, which may represent a systemic disorder or secondary conditions. Additional studies are currently underway to determine diagnostic signs and the underlying cause of this avian keratin disorder.

Habitat selection theory predicts that individuals choose breeding habitats that maximize fitness returns on the basis of indirect environmental cues at multiple spatial scales. We performed a 3-year field experiment to evaluate five alternative hypotheses regarding whether individuals choose breeding territories in heterogeneous landscapes on the basis of (1) shrub cover within a site, (2) forest land-cover pattern surrounding a site, (3) conspecific song cues during prebreeding settlement periods, (4) a combination of these factors, and (5) interactions among these factors. We tested hypotheses with playbacks of conspecific song across a gradient of landscape pattern and shrub density and evaluated changes in territory occupancy patterns in a forest-nesting passerine, the Black-throated Blue Warbler (Dendroica caerulescens). Our results support the hypothesis that vegetation structure plays a primary role during presettlement periods in determining occupancy patterns in this species. Further, both occupancy rates and territory turnover were affected by an interaction between local shrub density and amount of forest in the surrounding landscape, but not by interactions between habitat cues and social cues. Although previous studies of this species in unfragmented landscapes found that social postbreeding song cues played a key role in determining territory settlement, our prebreeding playbacks were not associated with territory occupancy or turnover. Our results suggest that in heterogeneous landscapes during spring settlement, vegetation structure may be a more reliable signal of reproductive performance than the physical location of other individuals.

Birds are generally unable to predict future changes in habitat condition when selecting nesting locations, and few studies have investigated the effect on birds of shifting habitat quality within nesting seasons. Anthropogenically influenced habitats such as agricultural landscapes are often associated with large shifts in quality that turn initially good habitat into poor habitat. We examined whether daily survival rates of Barn Owl (Tyto alba) nests in an agricultural landscape were influenced negatively by temporal instability in habitat conditions resulting from crop harvest. Although most nesting attempts by Barn Owls in our study area were initiated before the onset of harvest, fields adjacent to the majority of active nest boxes were harvested at some point during nesting attempts. Overall nest survivorship, as well as survivorship of individual nestlings within broods, was lower following harvest, likely because of associated declines in the abundance of rodents, the primary food source of Barn Owls. Nestlings in nests surrounded by harvested fields were generally lighter before fledging than young in nests surrounded by standing sugarcane and their associated dense rodent populations. Although instability of habitat quality in our study area was associated with reduced survivorship of individual Barn Owl nests, a population-level effect is unlikely given the overall fecundity of the population.

We investigated the effect of spring temperatures, female age, and female body condition on the timing of laying in a migratory woodpecker, the Northern Flicker (Colaptes auratus), and looked at the relationship between laying date and reproductive success. Average annual laying dates in the population, recorded over 12 years, were not related to the North Atlantic Oscillation or the Pacific-North American climate indices but were earlier when average daily temperatures along the migration route of Northern Flickers along the Pacific coast of North America were warmer. However, the strongest negative correlation between laying dates and ambient temperatures occurred after the arrival of most birds on the breeding site, which suggests that the ability of females to accumulate resources for egg laying on the breeding site was an important determinant of laying times. At the population level, egg laying advanced by 1.15 days for every degree warmer on the breeding grounds. At the level of individuals, laying dates advanced as females aged from 1 to 3 years, and females in better body condition also laid earlier. However, there was no interaction between female age and ambient temperature, which suggests that the age classes had equal capacity to respond to environmental change. Reproductive output declined seasonally as a result of declines in clutch size and not as a result of reduced fledging success. This suggests that there is no ecological mismatch linked to prey availability for Northern Flickers and that individuals could benefit by laying earlier if spring temperatures allow.

Birds with single-sex incubation must resolve tradeoffs in time allocated between incubation and foraging by adopting optimal incubation strategies. We used temperature loggers to study the incubation behavior of the Blood Pheasant (Ithaginis cruentus), a uniparental bird of high-elevation forests (3,000 m), at Lianhaushan Nature Reserve in southern Gansu Province, China. The incubation period, 37 days, was 8–10 days longer than for captive birds. Females usually took one recess averaging 6.6 ± 1.2 h day^-1, only 6.4% of the days had second recesses, and the latter averaged 28 ± 5 min. Females left the nests near dawn (at 0652 hours, on average) and returned around midday, at 1325 hours; in total, they remained on the nest (i.e., nest attentiveness) for 72.0 ± 1.4% of the day. Egg prédation was not associated with movements of females to and from nests. Egg temperatures dropped rapidly once females left the nest, and eggs often experienced 3.5 h below 10°C for each daily recess. Embryonic hypothermia was thus common, but the hatching rate was >90%. This degree of embryonic hypothermia has rarely been reported. It may be related to the time that Blood Pheasants need to forage on and process their low-quality foods, primarily mosses.

The Bahama subspecies of the Yellow-throated Warbler (Dendroica dominica flavescens) was originally described as a species. However, it was later reclassified as a subspecies, in part because the trinomial was considered useful for demonstrating relationships. Although flavescens has been widely reported as diagnostic in plumage and distinctive in ecology, it has remained a subspecies of D. dominica, perhaps because of the notion that its song is similar to that of continental dominica. We investigated the taxonomic status of flavescens by examining morphological, song, and genetic data. We found statistically significant differences between flavescens and continental dominica in wing chord and in bill, tarsus, and tail lengths. Discriminant function analysis correctly predicted 100% of flavescens individuals using morphological characters. Contrary to earlier accounts, we also found the ascending song of flavescens to be diagnosable from the descending song of continental dominica. Mitochondrial control-region sequence data revealed fixed differences and a 1.0% divergence between flavescens and continental dominica. Phylogenetic analysis indicated that flavescens samples form a monophyletic group and that continental dominica is paraphyletic with respect to flavescens. This is consistent with a scenario of peripatric speciation: complete lineage sorting in the flavescens population but incomplete lineage sorting in the much larger continental dominica population. We conclude that flavescens satisfies the requirements of both the biological and phylogenetic species concepts, and we therefore recommend that flavescens be reclassified as a separate species, the Bahama Warbler (Dendroica flavescens).