Hatchlings use egg teeth to help break through the shell during hatching, but these structures could have an additional function of increasing nestlings' visibility. I investigated the size, color, and persistence of egg teeth in woodpeckers, which nest in dark cavities. Many species of woodpecker have two egg teeth, one each on the tip of the maxilla and of the mandible, which, together with the pale flanges, frame the open mouth when nestlings gape. A spectrometer confirmed that reflectance of Northern Flicker (Colaptes auratus) egg teeth is higher than that of the flanges across a wide range of wavelengths, reaching nearly 100% reflectance in the wavelengths most visible to woodpeckers. Reflectance of flanges peaked in the ultraviolet, which is less visible to woodpeckers. Therefore, parent woodpeckers can probably see egg teeth better than flanges. Within a brood, the brightness of egg teeth or flanges was not dependent on nestlings' size (hatching order), suggesting these structures are not cues of nestlings' quality. Flickers retained upper egg teeth until fledging, but the size of egg teeth did not increase after hatching. A review of the literature suggests some burrow-nesting seabirds also retain egg teeth for a long time, reinforcing the idea that egg-tooth reflectance may have evolved independently in several phylogenetic groups in which parents must find nestlings in the dark.

The major forces of food and predation shape fitness-enhancing decisions of birds at all stages of their life cycles. During the breeding season, birds can minimize nest loss due to predation by selecting sites with a lower probability of predation. To understand the environmental and social aspects and consequences of breedingsite selection in prairie birds, we explored variation in nest-survival patterns of the Lark Bunting (Calamospiza melanocorys) in the shortgrass prairie region of North America. Over four breeding seasons, we documented the survival of 405 nests, conducted 60 surveys to estimate bird densities, and measured several vegetative features to describe habitat structure in 24 randomly selected study plots. Nest survival varied with the buntings' density as described by a quadratic polynomial, increasing with density below 1.5 birds ha^-1 and decreasing with density between 1.5 and 3 birds ha^-1, suggesting that an optimal range of densities favors reproductive success of the Lark Bunting, which nests semi-colonially. Nest survival also increased with increasing vegetation structure of study plots and varied with age of the nest, increasing during early incubation and late in the nestling stage and declining slightly from mid-incubation to the middle of the nestling period. The existence of an optimal range of densities in this semi-colonial species can be elucidated by the “commodity-selection hypothesis” at low densities and density dependence at high densities.

Migratory shorebirds frequently forage and roost in agricultural habitats, where they may be exposed to cholinesterase-inhibiting pesticides. Exposure to organophosphorus and carbamate compounds, common anti-cholinesterases, can cause sublethal effects, even death. To evaluate exposure of migratory shorebirds to organophosphorus and carbamates, we sampled birds stopping over during migration in North America and wintering in South America. We compared plasma Cholinesterase activities and body masses of individuals captured at sites with no known sources of organophosphorus or carbamates to those captured in agricultural areas where agrochemicals were recommended for control of crop pests. In South America, plasma acetylcholinesterase and butyrylcholinesterase activity in Buff-breasted Sandpipers was lower at agricultural sites than at reference sites, indicating exposure to organophosphorus and carbamates. Results of plasma Cholinesterase reactivation assays and foot-wash analyses were inconclusive. A meta-analysis of six species revealed no widespread effect of agricultural chemicals on Cholinesterase activity. However, four of six species were negative for acetylcholinesterase and one of six for butyrylcholinesterase, indicating negative effects of pesticides on Cholinesterase activity in a subset of shorebirds. Exposure to Cholinesterase inhibitors can decrease body mass, but comparisons between treatments and hemispheres suggest that agrochemicals did not affect migratory shorebirds' body mass. Our study, one of the first to estimate of shorebirds' exposure to cholinesterase-inhibiting pesticides, suggests that shorebirds are being exposed to cholinesterase-inhibiting pesticides at specific sites in the winter range but not at migratory stopover sites. Future research should examine potential behavioral effects of exposure and identify other potential sites and levels of exposure.

Cumulative loss of habitat and long-term decline in the populations of the Lesser Prairie-Chicken (Tympanuchus pallidicinctus) have led to concerns for the species' viability throughout its range in the southern Great Plains. For more efficient conservation past and present distributions of genetic variation need to be understood. We examined the distribution of mitochondrial DNA (mtDNA) variation in the Lesser Prairie-Chicken across Kansas, Colorado, Oklahoma, and New Mexico. Throughout the range we found little genetic differentiation except for the population in New Mexico, which was significantly different from most other populations. We did, however, find significant isolation by distance at the rangewide scale (r = 0.698). We found no relationship between haplotype phylogeny and geography, and our analyses provide evidence for a post-glacial population expansion within the species that is consistent with the idea that speciation within Tympanuchus is recent. Conservation actions that increase the likelihood of genetically viable populations in the future should be evaluated for implementation.

When and how fledglings become independent are important issues in understanding the life history of long-lived seabirds. In this study, we investigated post-fledging care, development of foraging skills, and the ultimate causes of independence in juvenile Red-footed Boobies (Sula sula) on Dong Island, Xisha Archipelago, northern South China Sea, during 2007 and 2008. After fledging, juveniles took an average of 118 days to become independent; the post-fledging survival rate was 96%. Parents supplied the young with more food after they fledged (average 176 g day^-1) than before, but the mass fed per day declined significantly at the end of the post-fledging period. Juveniles' foraging trips lengthened progressively and probably served mainly to develop foraging skills, as 94% of their food was supplied by their parents. Juveniles foraged for themselves mostly from 60 days post-fledging onward, which was just adequate for survival at independence. Fledglings became independent when foraging was energetically more profitable than begging food from the parents, whereas parents significantly reduced the mass of food delivered to the fledgling when the fitness increment from another nesting exceeded that from attending their current young. Nonsystematic checking of the nest area showed that at least 60% of fledglings still survived 20 to 84 days after independence, indicating that the strategy for achieving independence is successful. This study is the first to analyze the independence ontogeny of a long-lived seabird quantitatively.

Subspecies Calidris canutus islandica of the Red Knot breeds on the arctic tundra of northeastern Canada and northern Greenland and winters along the coasts of northwestern Europe. During northward migration, it stops over in either Iceland or northern Norway. It has been assumed that it does the same during southward migration. Using ratios of stable carbon isotopes (δ13C) in whole blood, blood cells, and plasma, we investigated evidence for a stopover in Iceland en route from the breeding grounds to the Dutch Wadden Sea. With the expected diet (shellfish) and stopover duration at Iceland (12–15 days, maximum 17 days) and the turnover rates of blood cells (15.1 days) and plasma (6.0 days), Red Knots that stopped in Iceland should arrive with a blood (cell) δ13C midway between a tundra (-24.7‰) and a marine value (-14.0‰) and a plasma δ13C approaching the marine value (-15.3‰). However, many adults arriving at the Wadden Sea had δ13C ratios in blood (cells) and plasma below these levels, and some arrived with clear tundra signals in blood cells, suggesting that they skipped Iceland during southward migration. Surprisingly, available data suggest this also to be true for juveniles during their first southward migration. The δ13C signature of second-year birds confirmed that they oversummered in the Wadden Sea. Our findings contradict the largely untested idea that juvenile shorebirds make more stopovers than adults as well as the idea that the migration between the Nearctic and Europe is necessarily a two-leg process.

We report nest and chick survival and colony-site dynamics of the Least Tern (Sternula antillarum). These results are the first for the Caribbean and were derived with likelihood-based approaches from 4640 nests and 44 chicks fitted with transmitters monitored in 52 colonies at St. Croix, U.S. Virgin Islands, 2003–2006. Managed colonies excluded, overall daily nest survival (±SE) was 0.92 ± 0.03 (period survival = 0.18). Daily nest survival of managed colonies (fenced) was significantly higher (0.97 ± 0.02; period survival = 0.51). Variation in nest survival was best explained by a negative linear trend in daily survival, influenced by year, rain, large colony size, and nesting habitat. Daily nest-survival rates at sandy beaches (0.94 ± 0.02), offshore cays (0.93 ± 0.005), and saltflats (0.91 ± 0.02) did not differ significantly. The period survival of chicks was 0.30 ± 0.11. Estimated fledglings per nest attempt were 0.06. Demographic assessments suggested that higher reproductive rates are required for maintenance (λ ≥ 1). Managed colonies could meet nest-survival thresholds, but complementary measures are needed to increase chick survival. Our findings suggest that management should target sites harboring large colonies because they had higher nest success and higher probability of use in subsequent seasons. The colonies' site dynamics suggested that immigration from other populations is plausible. This possibility relaxes breeding-productivity thresholds and advocates for coordinated conservation among populations on neighboring islands. Estimates of age-specific survival and connectivity are needed for the status of the species to be assessed appropriately and conservation priorities set.

Anthropogenic changes in landscapes can favor generalist species adapted to human settlement, such as the Common Raven (Corvus corax), by providing new resources. Increased densities of predators can then negatively affect prey, especially rare or sensitive species. Jackson Hole and the upper Green River valley in western Wyoming are experiencing accelerated rates of human development due to tourism and natural gas development, respectively. Increased raven populations in these areas may negatively influence the Greater Sage-Grouse (Centrocercus urophasianus), a sensitive sagebrush specialist. We investigated landscape-level patterns in raven behavior and distribution and the correlation of the raven data with the grouse's reproductive success in western Wyoming. In our study areas towns provide ravens with supplemental food, water, and nest sites, leading to locally increased density but with apparently limited (<3 km) movement by ravens from towns to adjacent areas of undeveloped sagebrush. Raven density and occupancy were greatest in land covers with frequent human activity. In sagebrush with little human activity, raven density near incubating and brooding sage-grouse was elevated slightly relative to that expected and observed in sagebrush not known to hold grouse. Raven occupancy near sage-grouse nests and broods was more highly correlated with sage-grouse success than were raven density and behavior, suggesting that the majority of nest predation by ravens is most likely carried out by resident territorial individuals. Integrated region-wide improvement of sagebrush habitat, removal of anthropogenic subsidies, and perhaps removal or aversive conditioning of offending ravens might benefit sage-grouse populations in our study area.

The energy expenditure associated with breeding may have detrimental effects on the breeder's physiology. Some studies have focused on the relationship between breeding performance and health status, but information on the link with biochemical variables reflecting susceptibility to oxidative stress is scarce. Over two years (2005 and 2006), using several morphological, biochemical and hematological variables, we measured the association between several measures of breeding (laying date, clutch size, mean egg weight, brood size, number of fledglings, and mean weight before fledging) and health in the Great Tit (Parus major). The effect of raising a second brood on the breeders' physiological condition was also studied. Females' body-condition index tended to be positively correlated with breeding performance, whereas in males the correlation was negative. Females laying later had lower hematocrits and higher glutathione peroxidase activity (GSH-Px), and those raising larger broods had also higher GSH-Px activity and tended to have lower plasma protein. The effect of raising a second brood was reflected mostly in body reserves but varied by sex. Our study suggests that trade-offs between breeding activity and physiological condition of the sexes differ and that hematocrit and GSH-Px are sensitive indicators of the physiological condition of breeding females.

We examined the association of temporal and spatial factors with nest survival of Western Bluebirds (Sialia mexicana) nesting in tree cavities in ponderosa pine (Pinus ponderosa) forests along the east slope of the Cascade Mountains, Washington. All study areas were managed for timber production through planned harvests or postfire salvage logging. Bluebirds laid a mean clutch of 5.3 ± 0.1 (SE) eggs (n = 131), and successful nests fledged an average of 4.5 ± 0.2 young (n = 85). Using a model-selection framework, we found that nest survival was a function of clutch size and treatment and that there was a quadratic effect of nest age. Daily survival rates decreased after the onset of incubation, then increased through the nestling period, and were higher for clutches with ≥5 eggs and in stands that were burned and salvaged. Survivorship over the entire period for clutches (n = 131 nests) with ≤4, 5, and ≥6 eggs was 0.39 (95% CI: 0.11, 0.65), 0.61 (95% CI: 0.34, 0.80), and 0.71 (95% CI: 0.46, 0.85), respectively. Vegetation variables associated with nest sites did not significantly affect nest survival. Predation accounted for the most nest failures (34% of nests). We suggest that parental defense of nests accounts for the quadratic effect of nest age, with adult bluebirds defending nests more aggressively as nestlings approach fledging, and that bluebirds laying larger clutches are older, more experienced birds, resulting in greater nest survival.

Long-distance migration between nonbreeding and breeding grounds involves use of multiple stopover sites where birds must refuel to meet the energetic demands of migration. Migrant forest birds that encounter urban landscapes experience high levels of habitat fragmentation and often use small, isolated forest patches. We investigated factors influencing stopover duration (length of stay) and migratory departure of Swainson's Thrushes (Catharus ustulatus) using forest patches within an urban landscape in Columbus, Ohio. During May, 2004–2007, we fitted 69 Swainson's Thrushes with 0.66-g radio transmitters, experimentally relocated the birds to seven mature forest sites that varied in area and degree of urbanization and monitored each individual daily until it departed. Mean minimum stopover duration was 3.7 days (± 3.4 SD), ranging from 1 to 12 days. Stopover duration was negatively related to advancement of migration (Julian date) and energetic condition at capture, and departure from stopover sites was associated with low wind speed and declining barometric pressure. We found no difference in stopover duration across the seven urban sites despite large variation in forest area and degree of urbanization. Swainson's Thrushes had strong site tenacity at the five largest (11.9–38.4 ha) sites, where 100% of birds remained until migratory departure; in contrast, 28% of individuals left the smallest (0.7 and 4.5 ha) sites during stopover. Results suggest that patches of remnant forest within cities may provide Swainson's Thrushes with suitable stopover opportunities without strongly influencing their migratory schedule, but minimum area requirements may limit the thrushes' use of some patches.

We investigated the distinctiveness of males' song and the relationship between song variables and females' mate choice in the Golden-winged Warbler (Vermivora chrysoptera). We recorded the songs of 23 males and quantified them to examine performance-related traits and specific song content. We carried out discriminant function analysis to compare variation within and among males for characteristics of both song types I and II. We used microsatellite DNA to identify the parents of 62 nestlings from 17 nests. By assigning paternity to males in our population we could examine relationships between females' choice and variation in males' song by comparing characteristics of within- and extra-pair sires. While we were able to discriminate statistically between individual males' songs, we found no significant differences in song variables between the within- and extra-pair males at a given nest. Therefore, female Golden-winged Warblers do not appear to be using these differences in song in choosing a mate. Further research on the Golden-winged Warbler is needed to understand song function and to gain insight into this species' reproductive biology, both of which could have important conservation implications for this declining species.

Events in one season can have carryover effects on birds in a subsequent season. Little research has addressed how conditions where a bird winters influence it during migration. We investigated such carryover effects on Magnolia Warblers (Dendroica magnolia) captured during spring migration in northwestern Ohio. We examined signatures of stable carbon isotopes (δ¹³C) in feathers grown in the neotropics where the birds winter and hypothesized that drier habitats (as indicated by δ¹³C) would advance infection by avian hematozoa, delay migration, and depress energetic condition and extent of prealternate molt. The range of δ¹³C in feathers (-25.0‰ to -19.9‰) was similar to that published for tissues grown in winter by other nearctic-neotropical migrant songbirds, suggesting that the Magnolia Warblers we captured wintered over a range of xeric to mesic habitats. Nonetheless, we detected no significant relationships between habitat moisture (as indicated by δ¹³C in feathers) and spring migration timing (capture date), energetic condition at capture, number of molted wing coverts, or extent of black breast streaking in these Magnolia Warblers. Furthermore, we found no consistent relationships between δ¹³C in feathers and rates of hematozoan infection. Our data suggest that for the Magnolia Warbler, habitat moisture may not be the primary factor affecting the quality of the winter habitat or that in this species there may be no carryover effects in spring migration.

To characterize the nonbreeding habitat of Kirtland's Warbler (Dendroica kirtlandii) on Eleuthera, The Bahamas, we quantified the habitat at sites where we captured the warblers and compared these traits with those of random sites and sites of tall coppice. On the basis of a chronosequence of satellite imagery, 153 capture sites ranged in age from 3 to 28 years after human disturbance, mean 14.6 years ± 6.3 (SD). Capture sites had been abandoned after clearing (65%), converted to goat pasture (26%), burned (2%), or were young second growth following unknown disturbance (7%). Canopies in 104 capture plots were lower (mean 1.8 m) than canopies in random plots (mean 2.7 m) and plots of late-successional tall coppice (mean 6.3 m). At seven sites mean foliage density in capture plots was consistently greatest at 0.5 to 1.0 m height, but the sites were heterogeneous for other foliage-height classes <3 m and for time since disturbance, canopy height, stem density, and five ground-cover traits. Plots did not differ by the sex of the captured bird except for a difference (P = 0.05) in foliage density at heights <3 m. Kirtland's Warblers frequently consumed fruit (69% of 499 observations), especially from Lantana involucrata, Erithalis fruticosa, and Chiococca alba. Foliage of these plants was more abundant in capture plots than random plots. Because the warblers consume fruit extensively and fruit is more abundant in early successional habitat, this species, like other nearctic—neotropical migrants that breed in early successional habitats, is absent from mature forests on the wintering grounds.

For migratory birds, the selection of high-quality breeding and nonbreeding habitats has significant implications for fitness. One potential reflection of habitat quality is body condition. Condition may influence adults' survival, a key demographic variable for population growth. Access to abundant resources should lead to good condition and birds maintaining or improving their condition over time. As many species use multiple habitats, recognizing the relative quality of these alternative environments is important for understanding population dynamics and aiding conservation. One species that uses a range of habitats is Swainson's Warbler (Limnothlypis swainsonii), a species of conservation concern that breeds in the southeastern U.S. From 2004 through 2007, we studied survival and body condition of Swainson's Warblers at three sites in eastern Arkansas, two dominated by mature forest, and one in an industrial forest managed for timber production. Birds in better condition at initial capture survived at a higher rate at two of three locations. Moreover, at all sites the birds' body condition improved through the breeding season and varied little by site. Body condition was positively related to dense understory vegetation and negatively related to herbaceous ground cover. Our results suggest that both mature and industrial forests may provide adequate habitat for Swainson's Warbler. Because of the relationship between body condition and survival, the observed habitat-related differences in body condition have implications for habitat quality. To provide high-quality habitat for Swainson's Warbler, management should focus on providing forests with dense understory vegetation and, to facilitate efficient foraging, little herbaceous ground cover.

Understanding factors affecting space-use patterns can lead to improved knowledge of the ecology and habitat needs of a species. We radiotracked 37 male Swainson's Warblers (Limnothlypis swainsonii) at two sites in eastern Arkansas, White River National Wildlife Refuge, a bottomland site, and St. Francis National Forest, a site with birds in both bottomlands and uplands. We found substantial variation in home-range size and evaluated habitat and nonhabitat predictors of home-range size by information-theoretic techniques. We also evaluated how breeding phase affected home-range size. Several habitat variables were good predictors of home-range size, including understory density, vine-stem density, and other stem-density variables. Overall, vine-stem density and understory density were the best predictors of home-range size, and nonhabitat factors were poor predictors. A three-variable model including density of giant cane (Arundinaria gigantea), vine, and shrub stems as separate variables was a much better predictor of home-range size than a model using total stem density, suggesting that Swainson's Warblers respond differently to different stem types. Birds using areas with fewer vines and more cane exploited smaller home ranges, suggesting better habitat quality. Birds that were tracked a greater proportion of time during the incubation and nestling periods used larger home ranges. Though our study found that birds held smaller home ranges in areas of more cane and fewer vines, a combination of stem factors and understory density appears to explain home-range size best. We recommend that management for Swainson's Warbler focus on maintenance of uniformly dense understory vegetation within forests.

The Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) breeds in coastal marshes of the mid-Atlantic United States. During the nonbreeding season, these marshes are occupied by this subspecies and the two interior-breeding subspecies M. g. georgiana and M. g. ericrypta (collectively, interior Swamp Sparrows). From September to May, 2005–2006 and 2007–2008, we surveyed marshes in which nigrescens breeds; >90% of these birds had been color-banded by the end of the previous breeding season. This allowed us to determine the nonbreeding occupancy of the breeding site by individuals that bred locally, Coastal Plain Swamp Sparrows that did not breed there, and interior Swamp Sparrows. Locally breeding birds disappeared from the breeding site by mid-October, although nonlocal nigrescens occupied it from October to late November. Locally breeding birds reappeared in April without any pulse of migration of nigrescens. Interior-breeding sparrows were abundant in the autumn and appeared in smaller numbers later in the nonbreeding season. The seasonal pattern of nigrescens was similar in both years, and its departure and arrival dates appear to coincide with changes in the frequency of freezing temperatures. The temporal pattern of interior Swamp Sparrows in the two years was more varied. Finally, during the autumn peak of Swamp Sparrow migration, the subspecies tended strongly to segregate in subspecies-specific flocks, suggesting that Swamp Sparrows preferentially interact with morphologically similar birds, a behavior which may have implications for divergence in species recognition mechanisms and speciation.

West Nile virus (WNV) infection has caused high levels of mortality in North American hawks and owls. To investigate the extent of infection among raptors of conservation concern in the Sierra Nevada, we tested 62 Northern Goshawks (Accipiter gentilis), 209 Spotted Owls (Strix occidentalis), and 22 Great Gray Owls (Strix nebulosa) for WNV antibodies during the summers of 2004 to 2007 and compared our results with avian WNV mortalities detected by the California Department of Public Health. We detected no antibodies to WNV among the individuals tested. During the same period WNV RNA was detected in dead birds from 26 species in the Sierra Nevada region. These results suggest that the populations we studied were not exposed, that the level of WNV infection was so low as to be undetectable by our sampling scheme, or that the mortality rate from WNV was high enough to leave no surviving individuals; there is no independent evidence of the last alternative.

While diving, small alcids appear wet, suggesting that their feathers repel water poorly. Nevertheless, once wet, their plumage resists water penetration effectively. This study's objective was to evaluate the effect of feather wetting on the critical penetration pressure of air (maximum pressure for resistance to air penetration, P_a) and water (P_w). We measured these values in breast feathers of Xantus's Murrelet (Synthliboramphus hypoleucus) and Cassin's Auklet (Ptychoramphus aleuticus) under two conditions : dry (feathers with separated barbs) and wet on one side (feathers with aggregated barbs). Dry feathers of both alcids did not resist air penetration at any pressure, but feathers wet on one side resisted 1.25 kPa. For Xantus's Murrelet P_w was 1.44 kPa, for Cassin's Auklet 1.36 kPa. These results support the hypothesis that plumages that appear wet could minimize heat loss by reducing the exchange of air within the plumage while the bird is diving.

Thripadectes treehunters are among the most poorly known cavity-nesting furnariids. In this paper we review the existing information on their nests, present new field observations from Ecuador, and add unpublished museum data. We describe for the first time the nests of two species, T. flammulatus and T. holostictus. Nests of Thripadectes are all shallow cups of vegetative material, lacking any lining of animal origin such as feathers or hair. Most species have consistent preferences for particular plant materials. Thripadectes rufobrunneus, T. virgaticeps, and T. holostictus use mainly rootlets, T. melanorhynchus uses stems of compound leaves exclusively, and T. flammulatus incorporates plant materials derived from grass, bamboo, and treeferns. Larger samples of nests from across these species' ranges are needed to determine the generality of this pattern and whether the availability of material plays a role. Several features of Thripadectes nest architecture are shared by putative sister genera Automolus, Hylocryptus, and Hyloctistes.