Long-term monitoring is essential to understand the effect of environmental change on bird populations. Ornithological field stations that have recorded detailed demographic data on bird populations over decades are well positioned to make important contributions to emerging research questions. On the basis of our experience at PRBO Conservation Science's Palomarin Field Station and a review of the literature, we assess the ability of field stations to use their long-term data to address current and future issues in conservation and management. We identify barriers to the application of data from field stations as well as some of the unique contributions made by these stations, and we present recommendations regarding the development, maintenance, and enhanced application of long-term data.

We evaluated how grazing affects bird assemblages in short and tall coastal salty grasslands at Samborombón Bay, Argentina. We studied ranches with three patterns of grazing (spatial rotation, continuous, and winter grazing) and a control site, at each censusing birds and surveying vegetation monthly. Results allowed us to compare the various treatments and their effects on endangered birds of short and tall grassland. Three species of special conservation concern showed significant responses to grazing. In short grasslands, the Buffbreasted Sandpiper (Tryngites subruficollis) is supported by continuous grazing. In tall grasslands, the Bay-capped Wren-Spinetail (Spartonoica maluroides) uses only grasslands with extensive cover of tall grass, whereas Hudson's Canastero (Asthenes hudsoni) uses those with high levels of cattle grazing. The diverse responses of grassland birds to grazing of different types of grassland leads us to propose a system of heterogeneous grazing that optimizes both production and conservation of grassland birds.

Quantifying the spatial genetic structure of highly vagile species of birds is important in predicting their degree of population demographic and genetic independence during changing environmental conditions, and in assessing their abundance and distribution. In the western Arctic, Lesser Snow Geese (Chen caerulescens caerulescens) provide an example useful for evaluating spatial population genetic structure and the relative contribution of male and female philopatry to breeding and wintering locales. We analyzed biparentally inherited microsatellite loci and maternally inherited mtDNA sequences from geese breeding at Wrangel Island (Russia) and Banks Island (Canada) to estimate gene flow among populations whose geographic overlap during breeding and winter differ. Significant differences in the frequencies of mtDNA haplotypes contrast with the homogeneity of allele frequencies for microsatellite loci. Coalescence simulations revealed high variability and asymmetry between males and females in rates and direction of gene flow between populations. Our results highlight the importance of wintering areas to demographic independence and spatial genetic structure of these populations. Male-mediated gene flow among the populations on northern Wrangel Island, southern Wrangel Island, and Banks Island has been substantial. A high rate of female-mediated gene flow from southern Wrangel Island to Banks Island suggests that population exchange can be achieved when populations winter in a common area. Conversely, when birds from different breeding populations do not share a common wintering area, the probability of population exchange is likely to be dramatically reduced.

Divergent selection can lead to substantial morphological and behavioral differences despite slight differentiation in neutral genetic variation. We examined the evolutionary history of two closely related waterfowl, the Cinnamon Teal (Anas cyanoptera) and Blue-winged Teal (A. discors), that are morphologically distinct but paraphyletic in mitochondrial DNA (mtDNA) and share allozyme alleles. Sequences of mtDNA and two nuclear introns revealed that North American Cinnamon Teal (n = 70) and Blue-winged Teal (n = 76) are characterized by high genetic diversity, a large effective population size, and recent population expansion. In contrast, South American Cinnamon Teal (n = 102) have less genetic diversity and a smaller effective population size that has been more stable. We found 91 unique mtDNA haplotypes, only a few of which were shared by the two species or the three subspecies of the Cinnamon Teal, but the haplotypes were intermixed in a polyphyletic relationship, and we found no diagnostic phylogroups. Moreover, populations were more strongly differentiated in mtDNA (Φ_ST = 0.41) than in the nuclear introns (Φ_ST = 0.04–0.06). Analyses of isolation with migration indicated that sharing of haplotypes and alleles in the two continents is more likely attributable to incomplete lineage sorting than to gene flow, whereas estimates within each continent yielded higher migration rates. The oldest divergence was between North American Cinnamon Teal and the other taxa, whereas the Blue-winged Teal likely split from South American Cinnamon Teal more recently. Considerable overlap in confidence intervals for these divergences, however, suggests that these taxa diversified rapidly.

The status and distribution of the Osprey (Pandion haliaetus) in Japan is poorly known, although it is considered as a near threatened species nationally. We studied the status, distribution and habitat characteristics of Ospreys breeding in Hokkaido, the northern island of Japan, from 2002 to 2003. During this period we located 62 Osprey nests and confirmed breeding in 8 of 14 districts of Hokkaido, indicating a sizable population breeding in Japan. Most Ospreys occurred in the western part of Hokkaido. We also found nests in two northern (16%) and one central (16%) districts, where breeding had not previously been confirmed, possibly representing a range expansion or previous underreporting. More than half of all nest sites (n = 35) were on rocks or cliffs, while elsewhere in the world nests in such situations appear to be scarce. The distribution of nesting Ospreys is concentrated where the frequency of the White-tailed Eagle (Haliaeetus albicilla) is lower, suggesting that the Osprey's range in these areas is restricted by avoidance of competition with or predation by eagles. The breeding population should be carefully monitored, because human activity at breeding sites or associated foraging sites could affect the population trend.

We used feathers from adult Gyrfalcons (Falco rusticolus) molted in breeding territories and blood samples from nestlings to document nest-site fidelity and dispersal of breeding adults and juveniles at three areas 100– 350 km apart in Yukon Delta National Wildlife Refuge, Alaska, 2003–2007. We used genotypes from seven polymorphic microsatellite loci that provided a mean probability of identity of 0.91 × 10^-5. Breeding Gyrfalcons were highly faithful to study area and territory; we documented no dispersals of breeding birds among study areas and only one dispersal between territories. But their fidelity to nest sites was low; 22% of birds returned to the same nest site the following year. Distance among alternate nests within a territory averaged 750 m and was similar for both sexes. Mean tenure in a territory was 2.8 years, similar for both sexes, and distributed bimodally with peaks at 1 and 4 years. Mean annual turnover rate at the Ingakslugwat Hills (Volcanoes) study area was 20%. We detected three young that established breeding territories at distances ranging from 0 to 254 km from their natal territory, representing 2.5% apparent recruitment. Gyrfalcons in the Askinuk Mountains study area were slightly but statistically significantly differentiated genetically from those in the Volcanoes and Kilbuck Mountain study areas. These data are the first published on the nest-site fidelity, breeding dispersal, and natal dispersal of the Gyrfalcon in North America and demonstrate the utility of noninvasive genetic sampling to greatly improve our understanding of avian dispersal and its underlying mechanisms.

Relatively little is known about shorebird movements across the coast of northern Alaska, yet postbreeding shorebirds use this coastline extensively prior to fall migration. We deployed 346 radio transmitters on 153 breeding and 193 postbreeding shorebirds of five species from 2005 to 2007.We examined two hypotheses regarding postbreeding shorebirds' movements: (1) whether such movements reflect ultimate routes of southbound migration and (2) whether migration strategy (length of flights) or timing of molt in relation to migration (molt occurring in breeding or winter range) are more influential in determining postbreeding shorebirds' behavior. Semipalmated Sandpipers (Calidris pusilla) moved east, consistent with the direction of their ultimate migration, but patterns of other species' movements did not reflect ultimate migration direction. Timing of postnuptial molt appeared to have more influence over residence time and movements than did migration strategy. Postcapture residence time for the Semipalmated Sandpiper was less than for the Western Sandpiper (C. mauri) and significantly less than for Dunlin (C. alpina), and the Semipalmated Sandpiper's movements between were quicker and more frequent than those of the Dunlin. We expected to see the opposite patterns if migration strategy were more influential. Our data shed light on how different shorebird species use the northern Alaska coast after breeding: most species are likely to be stopping over at postbreeding areas, whereas the Dunlin and some Western Sandpipers may be staging. We suggest the coast of northern Alaska be viewed as an interconnected network of postbreeding sites that serve multiple populations of breeding shorebirds.

Studies of seabird diets may reveal subtle ways in which sympatric species partition resources to facilitate co-existence. We studied the variability and partitioning of diets between the Herring (Larus argentatus) and Great Black-backed Gulls (L. marinus), both generalist predators, during incubation and early chick rearing on Kent Island, Bay of Fundy, Canada. We assessed diets from pellets collected around nests, regurgitates from captured birds, and stable-isotope analysis of prey items and tissues (blood and feathers) obtained from chicks and adults. Pellet analyses indicated that both species relied primarily on fish (28 to 45% of identified prey items) and crabs (15 to 43%). Stable-isotope analyses showed that the Great Black-backed Gull fed at a higher trophic level than the Herring Gull, both species fed at higher trophic levels during breeding than during nonbreeding, and both species has similar preferences for feeding inshore vs. offshore and in terrestrial vs. marine habitats. Contrary to previous research, we found that chicks were fed from a lower trophic level than where adults feed. Models of isotopic mixing estimating the proportion of assimilated diets were generally consistent with the pellet analysis for adults but revealed that both species fed their chicks more krill (>60%; Meganyctiphanes norvegica) and mackerel (>20%; Scomber scombrus) than adults consumed; adults may selectively provision their young with easily digestible prey and prey of high energy content. Our results reveal evidence of dietary partitioning between species and age classes, and highlight the strengths and biases associated with techniques for sampling gulls' diet.

The Rufous-tailed Hummingbird (Amazilia tzacatl) is a common resident of the neotropical lowlands of Middle America and northern South America. The Escudo Hummingbird (A. t. handleyi), the most distinctive of the five subspecies of A. tzacatl, is endemic to Isla Escudo in Caribbean western Panama. Mitochondrial DNA (mtDNA) sequence variation from across most of the species' range showed five well-defined but shallow clades (maximum uncorrected distance 2.4%) that only partially agreed with subspecific taxonomy. A widespread Middle American clade ranges from southeastern Mexico to central Caribbean Panama and includes birds collected on the Bocas del Toro archipelago. The Escudo Hummingbird fell within this clade and was slightly differentiated (two unique substitutions; uncorrected distance ∼0.2–0.5%). Two additional clades occur in the Pacific regions of southern Middle America. A fourth clade is endemic to eastern Panama (eastern Panamá and Darién provinces); a fifth is found in northwestern South America and in Darién. Secondary contact between clades occurs at three sites: between clades I and III in northwestern Costa Rica, between clades I and II in western Panama, and between clades IV and V near the Panama-Colombia border. The last case is likely due to recent expansion into the region from two directions. Thus the history of Amazilia tzacatl demonstrates a tendency for the formation of monophyletic mtDNA clades, likely as the result of geographic isolation, but also a propensity for secondary contact of these clades, a phenomenon recovered in many other phylogeographic studies of neotropical birds.

In eastern North America, after the young fledge, both adult and juvenile mature-forest birds may use regenerating clearcuts, although which species frequent early-successional forest and during which life stages is not well documented. To assess whether birds nesting in mature forest in north-central Minnesota use regenerating clearcuts 2–10 years old, we netted after birds fledged (2006–2009) and during the breeding season (2009). In addition, we monitored Ovenbird (Seiurus aurocapilla) nests and banded nestlings in adjacent mature forest and estimated the age at which juveniles used regenerating clearcuts. While banding, we also recorded nests of any species encountered opportunistically in regenerating clearcuts as evidence of breeding in this cover type. During July and August, we captured 4556 birds of 62 species, of which 1746 (38%) were of 28 mature-forest species. As reported elsewhere, most (76%) mature-forest birds we captured were of only a few species: Ovenbird, American Redstart (Setophaga ruticilla), Least Flycatcher (Empidonax minimus), and Black-and-white Warbler (Mniotilta varia). In 2009, 21% of captures during the nesting period were of mature-forest birds. Comparing dates of fledging from monitored nests to dates of capture in clearcuts implies that nearly all (95%) hatch-year Ovenbirds using clearcuts were independent of adult care. Capture dates of juveniles of other mature-forest species were similar. Although we captured 340 hatch-year Ovenbirds in regenerating clearcuts, we captured only one of 424 Ovenbirds we had banded as nestlings in adjacent mature forest. Within the clearcuts, we encountered nests of five species that typically nest in mature forest.

Variation in the risk of predation to offspring can influence the expression of reproductive strategies both within and among species. Appropriate expression of reproductive strategies in environments that differ in predation risk can have clear advantages for fitness. Although adult-predation risk appears to influence glucocorticosteroid levels, leading to changes in behavioral and life-history strategies, the influence of offspring-predation risk on adult glucocorticosteroid levels remains unclear. We compared total baseline corticosterone concentrations in Gray-headed Juncos (Junco hyemalis dorsalis) nesting on plots with and without experimentally reduced risk of nest predation. Despite differences in risk between treatments, we failed to find differences in total baseline corticosterone concentrations. When we examined corticosterone concentrations across a suite of sympatric species, however, higher risk of nest predation correlated with higher total baseline corticosterone levels. As found previously, total baseline corticosterone was negatively correlated with body condition and positively correlated with date of sampling. However, we also found that corticosterone levels increased seasonally, independent of stage of breeding. Nest predation can alter the expression of birds' reproductive strategies, but our findings suggest that total baseline corticosterone is not the physiological mechanism regulating these responses.

Estimates of productivity usually ignore survival during the postfledging period, the time between a bird's leaving its nest and departure for migration or movement to an area for wintering. During the first 1–3 weeks after fledging, young birds are limited in mobility, making them vulnerable to fatality, especially from predation. To help fill this information gap, we examined the period of postfledging dependence of the Willow (Empidonax traillii) and Dusky (E. oberholseri) Flycatchers in the central Sierra Nevada, California. For fledglings we examined factors that influenced survival, movements, and habitat use and home-range size. We observed family groups daily during the postfledging dependence period and resighted individual band combinations. Fledglings' survival ranged from 46% to 76% and varied by year and species. Fledglings moved on average 45 m from the nest per day during the dependence period. We detected family groups in their natal meadows from 13 to 33 days. We detected Willow Flycatchers in riparian shrubs 94% of the time, along the upland forest edge for the remaining 6%. We detected Dusky Flycatchers in riparian shrubs 70% of the time, in upland forest for the remaining 30%. For both years of our study combined, mean 95% home-range sizes were 1.80 ± 1.44 (SD) ha for the Willow Flycatcher and 1.82 ± 1.70 ha for the Dusky Flycatcher. Mean 50% core areas were 0.33 ± 0.27 ha for the Willow Flycatcher and 0.38 ± 0.44 ha for the Dusky Flycatcher.

Using multiple-covariate distance sampling with seasonal point transects, we surveyed for the Western Scrub-Jay (Aphelocoma californica californica group) over a substantial portion of its range in California . Our goals were to produce seasonal and habitat-specific estimates of the scrub-jay's regional density and abundance in 2008 and to demonstrate how the concurrent collection and analysis of covariate data may be useful in improving estimates of bird density. Density and abundance estimates implied a significant 38% increase over 2008, from a low of 24 jays km^-2 (2.3 × 10⁶ jays) in February to a high of 78 jays km^-2 (7.5 × 10⁶ jays) in November. Density was greatest in agricultural habitats (98 jays km^-2) and least in rural habitats (38 jays km^-2). Averaged over the study, abundance was greatest in agricultural habitats (2.6 × 10⁶ jays) and least in urban habitats (3.6 ×10⁵ jays). Inclusion of covariates such as habitat type, observer, weather, and time of day often increased the precision of density estimates, and it significantly improved model results in one case. As detailed in this study, the techniques of multiple-covariate distance sampling may have application as effective and noninvasive methods for obtaining more precise estimates of bird density and monitoring the density and abundance of species across broad habitats.

Evolutionary theory predicts that exposure to more diverse pathogens will result in the evolution of a more robust immune response. We predicted that during the breeding season the innate immune function of female Tree Swallows (Tachycineta. bicolor) should be more effective than that of males because (1) the transmission of sexually transmitted microbes during copulation puts females at greater risk because ejaculates move from males to females, (2) females copulate with multiple males, exposing them to the potentially pathogenic microbes in semen, and (3) females spend more time in the nest than do males so may be more exposed to nest microbes and ectoparasites that can be vectors of bacterial and viral pathogens. In addition, elevated testosterone in males may suppress immune function. We tested our prediction during the 2009 breeding season with microbicidal assays in vitro to assess the ability of the innate immune system to kill Escherichia coli. The sexes did not differ in the ability of their whole blood to kill E. coli. We also found no significant relationships between the ability of whole blood to kill E. coli and the reproductive performance or the physical condition of males or females. These results indicate that during the nestling period there are no sexual differences in this component of the innate immune system. In addition, they suggest that there is little association between this component of innate immunity and the reproductive performance and physical condition during the nestling period of adult Tree Swallows.

Establishing migratory connectivity between migratory birds' breeding, wintering, and stopover sites is an important component of their effective conservation and management. For neotropical migrants, geographic origins and migration patterns have been poorly documented. During fall migration of 2009, we identified geographic origins of the Veery (Catharus fuscescens) at stopover sites in the Sierra Nevada de Santa Marta, northern Colombia, by analyzing stable hydrogen isotopes (δD) in feathers and from values expected from a long-term isoscape for North America of δD in feathers. We evaluated the importance of the Sierra Nevada de Santa Marta to the Veery on the basis of the birds' geographic origins and assessed the relationship between timing of migration and geographic origins and age. We estimated that 100 of the 197 individuals captured originated from the southwest and/or the northeast regions of their breeding range, but applying abundance in the breeding range as an informed prior probability further delimited the potential origin of 183 individuals and increased support for origins from the northeast. Feather δD and timing of arrival at the stopover sites were negatively correlated, suggesting a chain migration. Provided that there is no molt migration, adults originated primarily from the southernmost portion of the breeding range and arrived at the stopover site before hatch-year birds. Our study reveals the power of measurements of endogenous markers to clarify origins of birds captured during migration and suggests that Veeries converge on northern Colombia potentially from across the species' breeding range.

The taxonomy of Hauxwell's Thrush (Turdus hauxwelli) with respect to its relationship to the Cocoa Thrush (Turdus fumigatus) has been complicated. A confounding factor has been the morphological variation reported within T. hauxwelli and the apparent geographic overlap of the two taxa. Recent evidence shows that some of these factors may be explained by the existence of a cryptic, syntopic species, very similar in plumage to T. hauxwelli. The new species differs in minor plumage characters, in soft-part colors, and (especially) in voice. On the basis of vocal and molecular data, we propose that the new thrush is not particularly closely related to the T. fumigatus/hauxwelli complex but rather is the western Amazonian member of the Spectacled Thrush (T. nudigenis) complex. Our molecular phylogeny suggests that the new species is sister to the Unicolored Thrush (T. haplochrous) and also that the Ecuadorian Thrush (T. maculirostris) should be considered a species separate from the Spectacled Thrush. In the absence of modern, data-rich specimens, the new thrush might well have remained unknown. This hidden taxon provides yet another case that argues strongly for continuing the tradition of general specimen collection. Having removed the new species as a source of confusion, we suggest that a reevaluation of the species status of T. hauxwelli with respect to T. fumigatus is in order.

Whereas the ecological and evolutionary causes and consequences of sexual dimorphism in birds have been widely explored, the functional significance of female ornamentation in mutually ornamented species is less well understood. One hypothesis for mutual ornamentation is mutual sexual selection, where similar selective pressures shape the ornamental traits in both sexes. We examined multiple melanin-based plumage traits (chestnut-colored breast plumage, tail-spot size and damage) in male and female American Robins (Turdus migratorius) in relation to patterns of mating, individual quality, breeding performance, and incidence of extra-pair paternity. We found positive assortative social mating based on breast color and tail-spot damage. Tail-spot size was unrelated to patterns of social mating, and none of the plumage traits examined was associated with the incidence of extra-pair paternity. Brighter breast plumage and less damage to tail spots were positively associated with several measures of breeding performance in female American Robins. In males, body condition was positively correlated with breast color, but nest defense was actually lower in males with brighter breasts and less tail-spot damage. Although male and female ornamentation in the American Robin may be the product of mutual mate choice, further assessment of this hypothesis requires information on how an individual's parental investment is affected by its own and its mate's plumage and on how plumage varies with age.

The Swainson's Warbler (Limnothlypis swainsonii) is an insectivorous songbird and a species of conservation concern in the southeastern U.S. Because it is specialized for foraging in the litter of the forest floor, it is dependent on a well-developed leaf-litter layer. However, this reliance on the litter layer likely reflects selection of habitats with abundant arthropods for food. To investigate this possibility, we examined relationships between Swainson's Warbler presence and both abundance and diversity of ground-dwelling and litter arthropods. In 2004 and 2005, using song playbacks, we surveyed 1453 sites and collected arthropods in litter samples and pitfall traps at 45 randomly selected occupied and unoccupied sites. In litter samples, total mean arthropod abundance, abundance of arthropods ≥5 mm in length, total abundance of adults, and taxonomic richness were significantly greater at sites occupied by Swainson's Warblers than at unoccupied sites. In pitfall data, however, we detected no differences between occupied and unoccupied sites. Additionally, the abundance of several taxa known to be Swainson's Warbler food, most notably beetles, was greater at occupied than at unoccupied sites. Overall, the taxonomic richness and abundance of large arthropods were the best predictors of Swainson°s Warbler presence. These results suggest that arthropod abundance and taxonomic richness are key habitat components for Swainson's Warbler. Because the arthropod community may be a driving factor influencing the presence of Swainson's Warbler, management that maintains or improves the leaf-litter layer and promotes ground- and litter-dwelling arthropods will be beneficial for managing habitats for this and other ground-foraging species.

In urban landscapes, predators are often more abundant or diverse than in rural areas, but few studies have examined how the identity of actual nest predators varies with urbanization. From 2007 to 2010, we used time-lapsed video to record activity at nests of the Northern Cardinal (Cardinalis cardinalis), Acadian Flycatcher (Empidonax virescens), Gray Catbird (Dumetella carolinensis), and Wood Thrush (Hylocichla mustelina) in riparian forests in urban and rural landscapes of Ohio, and we examined the extent to which predator identity was predicted by landscape composition. In 99 records of depredation, we identified 21 species of nest predators (17 in rural, 15 in urban). No single species dominated, though the Brown-headed Cowbird (Molothrus ater; 18% of recorded depredations) and northern raccoon (Procyon lotor; 11%) were the most commonly recorded predators. Birds were responsible for 62% of depredations, followed by mammals (36%) and snakes (2%). By category of predator, mesopredators were the most likely to remove all nest contents, depredate nests at night, and concentrate on the nestling stage. Mesopredators also were most important in urban landscapes, accounting for 35% of urban but only 13% of rural depredations. Small birds (46%), including the cowbird, Common Grackle (Quiscalus quiscula), and House Wren (Troglodytes aedon), plus raptors (21%), were responsible for most rural depredations. The relative proportion of nests depredated by mesopredators increased as the landscape surrounding a forest urbanized. These data indicate that the composition of the actual predator community may not mirror patterns of abundance or diversity along the rural-to-urban gradient.

In some sexually dichromatic passerines, juvenile males retain a plumage similar to that of adult females through their first year or longer (delayed plumage maturation). The Tawny-bellied Seedeater (Sporophila hypoxantha) is a sexually dichromatic species in which, to the human eye, the juveniles look like females. We analyzed the species' stages of plumage maturation by reflectance spectrometry and a visual model of color discrimination on captive individuals of known ages. We found that males retain a plumage different from that of adult males through their first breeding season. By the time males passed the age of 1 year, their color did not differ from that of adult males in any region of the body except the crown. Spectrophotometry also revealed differences between the plumage color of juvenile males and females, and the color-discrimination model implies that the birds should be able to detect these differences. Thus juvenile males of the Tawny-bellied Seedeater acquire adult plumage after their first breeding season but are already dichromatic during the first year. How this pattern of plumage development affects the species' reproductive or other social behavior deserves further study.

Long-term studies over a variety of regions, species, and time periods can help link trends in climate to changes in bird phenology and provide better understanding of potential effects of climate change. We analyzed first spring arrival dates of 93 species of migrants from the Buffalo Ornithological Society's database covering the period from 1967 to 2008. Migrants appeared a mean 0.10 days earlier each year. Short-range migrants, traveling from a winter range within North America, have advanced their average arrival more, 0.15 days per year, than have long-range migrants from Central America, South America, or the West Indies, whose advance averaged 0.06 days per year. We regressed arrival dates against the temperature of short-range migrants' winter range, as represented by Houston, Texas, and the North American Oscillation Index as indicators of climate change. The Houston temperature correlates well with earlier arrival dates, especially for short-range migrants. We compared our results with similar studies across North America and found general agreement with the trends we observed. These results are consistent with the hypothesis that climate change has a strong influence on the phenology of bird migration.