Passerine birds on islands tend to have larger bills than their mainland relatives. The morphological shift may be related to reduced interspecific and increased intraspecific competition. Emberizid sparrows in North American salt marshes also show consistently greater bill size. We tested the hypothesis that passerines restricted to mangrove forests, another continental system with low species diversity and high population densities, also have larger bills than their closest nontidal relatives. We found a consistent pantropical pattern of longer and deeper bills in passerine birds restricted to mangroves. These results indicate that disproportionately longer bills in relation to body size in passerines restricted to coastal saline habitats, just like those found on islands, seems to be a general ecological rule. The similar pattern in bill morphology suggests that ecological and evolutionary processes thought to occur only in island systems might also occur in some continental systems.

Neighbor visibility is thought to influence territory size and shape, and visual obstructions may allow for greater nesting density within a breeding colony. We studied the effects of neighbor visibility and neighbor proximity on settlement patterns in a colony of Barn Swallows (Hirundo rustica) using artificial nest cups placed in parallel rows on the underside of a pier. Nest cups were placed 61 cm apart so that the distance between adjacent cups matched the distance between adjacent rows. Rows were separated by the vertical panels to which the nest cups were attached. To a swallow perched on a cup, cups in the same row were visible but cups in adjacent rows were visually obstructed. We compared the observed nest-settlement patterns with expected distributions generated both by calculating cup availability and by simulating random settlement events. Barn Swallows avoided settling 61 cm from an active nest only if that neighbor was visible; visually obstructed neighbors at the same distance were not avoided. Nest cups where the nearest neighbor was both visually obstructed and >61 cm away were occupied significantly more often than expected by chance. Barn Swallows thus consider both the proximity and visibility of established pairs when choosing nest sites within a colony.

Clark's Nutcracker (Nucifraga columbiana) is one of the most specialized scatter-hoarding birds, considered a seed disperser for four species of pines (Pinus spp.), as well as an obligate coevolved mutualist of Whitebark Pine (P. albicaulis). Cache-site selection has not been formally studied in Clark's Nutcrackers, which are considered effective seed dispersers for pines because past studies have found that they harvest and store large quantities of seeds. Although many seeds are placed in sites suitable for germination and establishment, information is lacking on the proportions of seeds placed in suitable versus unsuitable sites. We used radiotelemetry to investigate cache-site selection and evaluate the suitability of selected cache sites for establishment of Whitebark and Ponderosa (P. ponderosa) pines. On a landscape scale, Clark's Nutcrackers cached seeds centrally within home ranges, even though this required them to transport seeds up to 32.6 km. They selected low-elevation forests for caching, presumably because these sites accumulated little snow. When caching at high elevations, the birds placed most seeds in aboveground microsites. Only 15% of Whitebark Pine seed caches (n = 155 caches) were placed below ground and in habitats where seeds could germinate and seedlings grow. For comparative purposes, 42% of Ponderosa Pine seed caches were placed in suitable habitats and below ground. Although Whitebark Pine is an obligate mutualist of Clark's Nutcracker, our study suggests that Clark's Nutcrackers in some populations may be more effective seed dispersers for Ponderosa Pine than for Whitebark Pine.

White-winged Scoters (Melanitta fusca) and Surf Scoters (M. perspicillata) are often assumed to rely on similar marine resources. To evaluate the accuracy of this assumption, we contrast seasonal distributions, foraging effort, and indicators of energy status (body mass and composition, plasma metabolites) in three major foraging sites in Puget Sound, Washington, for these rapidly declining sea duck congeners. For Surf Scoters, distributions and energy status indicated that a mussel-dominated site was relatively important in early winter, but that importance shifted during late winter and spring to seagrass sites that provided either herring spawn or epifaunal invertebrates. As winter progressed, movements among foraging sites and increased foraging effort by Surf Scoters were accompanied by greater variability in their energy status compared with White-winged Scoters; body mass declined over winter by >9% in about one-third of past studies for Surf Scoters, well above the range of losses observed in White-winged Scoters. For White-winged Scoters, lower variability in energy status, foraging effort, and distributions throughout winter suggests that they are better able to regulate energy balance regardless of changing foraging conditions. Greater resistance to seasonal environmental changes in White-winged Scoters may be related to their >50% larger body size, which confers lower mass-specific energy costs and access to a wider size range of bivalve prey. Perhaps because of their greater sensitivity to winter foraging conditions, Surf Scoters appear to rely on a broader range of foraging sites than White-winged Scoters.

Incubation has a significant reproductive cost in birds that can limit both current and future reproductive success. We manipulated the incubation period of Wood Ducks (Aix sponsa) to examine how female body mass, incubation behavior, and nest temperature responded to changes in incubation costs. We found no relationships between the length of the incubation period and either the percent loss of body mass or the body mass at the end of incubation. However, females that initiated nests early in the season lost more body mass than females that nested later. The number of daily recesses increased slightly with longer incubation periods, but incubation constancy over the full incubation period and during the last week of incubation was not affected by incubation-period length. Variation in incubation constancy was explained best by nest initiation date. Incubation constancy was greatest for early-nesting females and declined for females that nested later. There also was a weak positive relationship between body mass and incubation constancy. Average nest temperature was not associated with the length of the incubation period but increased with increasing incubation constancy and as the breeding season progressed. Evidence from this study is consistent with the idea that incubation is an important reproductive cost that may constrain the timing of nest initiation in Wood Ducks. Poor-quality females, by delaying nest initiation, experienced reduced incubation costs and were able to maintain nest temperatures at levels similar to those of early-nesting females.

Many species endemic to isolated islands are of conservation interest because of concerns over the potentially devastating effects of environmental stochasticity and the pending threat of anthropogenic influences and invasive species. The effective size (N_e) of these species is a key parameter in their conservation because it predicts the detrimental effects of inbreeding or genetic drift and can be used to inform management plans. We used microsatellite allele frequencies (4 loci) and mtDNA (control region; cytochrome b) sequences to assess the genetic diversity and the effective number of breeders (N_b) in the Nihoa Millerbird (Acrocephalus familiaris kingi), a critically endangered passerine endemic to the northwest Hawaiian island of Nihoa. Using samples collected in 2007 and 2009, our results reveal extremely low levels of genetic diversity at both microsatellites and mtDNA, and both approximate Bayesian computation (ABC) and sibship methods indicate that the effective number of breeders (N_b) for this species is between 5 and 13 individuals. Our analysis highlights the utility of ABC and sibship methods for estimating N_e in species with low genetic polymorphism or few loci. We compare our results to a recent genetic study of this species and document the loss of alleles at two microsatellite loci and one unique mtDNA haplotype. We discuss our findings in the context of the planned translocation of Nihoa Millerbirds from Nihoa to Laysan Island.

The addition of planted grasslands (i.e., fields that have been planted with exotic grass and forb species) to the North American landscape has been beneficial for the conservation of many species, but not necessarily for species that show a preference for native grasslands. Under what conditions these planted fields are attractive to native grassland specialists is unclear. Sprague's Pipit (Anthus spragueii) is a native grassland specialist, but it breeds in planted grasslands in some parts of its range. We conducted a comparative study of territory and nest use by Sprague's Pipits in native pastures and planted hay fields from 2006 to 2008. In planted hay fields, territories were characterized by vegetation height of 25 cm and litter depth of <1.5 cm; in native pastures, the birds used territories with 15% bare ground and <1.5 cm litter depth. Nests in both habitats were located in areas with vegetation height of 25–30 cm, whereas random areas had either taller or shorter vegetation. Territories were associated with different vegetation characteristics in both habitats. Sprague's Pipits used the same nest characteristics in both habitat types, which suggests that they found areas within planted grasslands that closely resembled areas that they might use for nesting in native grasslands. Planted fields with a low amount of alfalfa and suitable vegetation height (20–30 cm) should be attractive to breeding Sprague's Pipits.

The effects of anthropogenic habitat modification are evident on tropical Pacific islands where forests have been extensively converted to plantations of Coconut Palm (Cocos nucifera). We evaluated resource selection in the critically endangered Tuamotu Kingfisher (Todiramphus gambieri gertrudae), which is confined to a single population on the low-elevation island of Niau Atoll in French Polynesia. Our analyses indicate that resources associated with foraging underlie space use and habitat selection of Tuamotu Kingfishers at multiple spatial scales. At the island scale, the occurrence of the species was best predicted by habitat features associated with foraging opportunities, including agricultural coconut forest with open understory, hunting perches, and exposed ground. Conversely, the species' distribution was negatively associated with undisturbed vegetation, including primary feo forest and fallow coconut plantation. At the home-range scale, utilization distributions of radiomarked Tuamotu Kingfishers also indicated that birds selected agricultural coconut forest and least preferred native feo forest. Observations further indicated that foraging birds selected coconut plantations managed with prescribed burning for hunting. The Tuamotu Kingfisher is a rare example of a threatened tropical species that likely benefits from agricultural management, and our findings provide support for conservation strategies based on establishing rescue populations on other islands with coconut plantations. We suggest that incorporating agricultural coconut forests into conservation planning could help prevent the extinction of several kingfisher species that historically relied on the natural broadleaf habitats that are now almost entirely absent from insular Pacific Oceania.

Despite recent increases in the number of demographic studies of birds in urban environments, the postfledging period remains poorly understood. Because novel ecological factors, including changes in predator abundance and invasive exotic shrubs, are associated with urbanization, we asked (1) how does postfledging survivorship vary across a rural-to-urban landscape gradient and (2) to what extent does Amur Honeysuckle (Lonicera maackii), an invasive exotic shrub, influence patterns of survivorship and habitat selection? During the 2008 and 2009 breeding seasons, we placed radiotransmitters on fledgling Northern Cardinals (Cardinalis cardinalis; n = 45) and Acadian Flycatchers (Empidonax virescens; n = 31) that occupied riparian forest stands embedded within a rural-to-urban landscape gradient in central Ohio, USA. Predation was the primary cause of fledgling mortality for both species, but cumulative survivorship (± SE) for Acadian Flycatchers (0.720 ± 0.097; 22 days) was 1.6 × that of Northern Cardinals (0.440 ± 0.077; 71 days). Survivorship across the entire postfledging period was not associated with urbanization, but during the initial 3 days after fledging, when mortality rates were highest, Northern Cardinal survivorship was positively related to urbanization. Northern Cardinals strongly selected for complex understory vegetation that was positively associated with survivorship, but survival was not related specifically to cover by Amur Honeysuckle. Contrary to assumptions that postfledging survival declines as landscapes urbanize, our results suggest that urban forests may provide suitable habitat for juvenile birds living within metropolitan areas.

We used stereo recordings of point counts from Breeding Bird Survey (BBS) routes to estimate inter-observer variability, to compare recordings with field observers, and to evaluate multiple-observer occupancy-model approaches to adjust for incomplete detection. We asked six birders with point-count experience (listeners) to listen to recordings of 80 stops from four BBS routes and report all the species they detected at each stop. Listeners went through each recording only once, without the use of aids such as spectrograms, to simulate field conditions. Listeners differed significantly in the mean number of species reported, ranging from 7.8 to 10.6 species per stop, compared with 12.6 confirmed on the recordings. On average, 14% of the reported records were identification errors (i.e., species not present on the recording), and 23% of species present on the recordings were overlooked. Field observers reported similar numbers of species as some listeners, but fewer species than were on the recordings. Multiple-observer occupancy models failed to correctly account for identification errors and tended to overestimate species richness by 1.0–8.4 species per stop; species-specific occupancy estimates were positively biased by 69–100%. Although inter-observer variability clearly needs to be considered in analysis of point-count data, multiple-observer occupancy models do not adequately correct for this variation. The number of species detected on recordings suggests that they have considerable potential to supplement current monitoring programs, but further development of analysis methods is required to address observer effects.

Energetic condition influences migratory decisions made by songbirds. Over-water or coastal flights are often the shortest routes but may be dangerous for landbirds because they may get caught over water where they are not able to rest and refuel. We investigated how various components of energetic condition were related to the likelihood that a migrant songbird in the Gulf of Maine region would initiate a migratory flight and the direction that it would choose. We used release tests and measurements of energy stores (fat score), plasma triglycerides, and within-day changes in body mass to investigate whether these measures of condition were related to the decisions migrants must make about when to resume migration and which direction they should go. Our results indicated that the amount of fat that a bird had at the time of release influenced the decision to initiate a flight, whereas directional decisions were influenced by both fat and within-day changes in body mass. Plasma triglyceride levels were higher in birds that initiated migratory flights; however, this does not appear to have influenced departure or directional decisions. These results indicate that migrant songbirds on stopover rely on cues about their energetic condition when making departure and orientation decisions and that the amount of fat a bird has may be the most relevant cue for these decisions.

In birds, molt duration is an important trait that can affect plumage functionality and, consequently, the fitness of individuals. However, knowledge about the factors that affect variation in molt speed is sparse, mostly because of the methodological difficulties of studying avian molt. We used a ptilochronology-based approach to estimate the rate at which tail feathers were produced during molt to shed light on the relationship between molt duration and feather growth rate. For that purpose, we used three data sets. First, we tested whether the average molt durations of 22 passerine species were correlated with the mean growth rates of their feathers, using both conventional and phylogenetically corrected statistical procedures. Second, we explored this same association among captive Great Tits (Parus major). And third, we took advantage of the biannual complete molt of Willow Warblers (Phylloscopus trochilus) to examine whether the feathers synthesized during their short summer molt grew faster than those produced during their long winter molt. Feather growth rates were negatively correlated with molt duration in all analyses, revealing that molt duration can be estimated from the growth rate of a single feather. However, predictive power was limited by the fact that molt duration is modulated mainly by molt intensity, which seems to be correlated with ecological constraints in our interspecific approach. We also discuss the implications of our results for the evolution of molt duration, and the potential application of ptilochronology in its study.

Feather molt is recognized as an energetically costly activity for birds, and parasite infestation during molt has the potential to reduce host fitness because parasites sequester essential nutrients and stimulate the immune system. We manipulated the coccidian parasite load of captive male House Sparrows (Passer domesticus) by suppressing the natural infection of control birds with an anticoccidial drug and infecting experimental birds with coccidian oocysts. Following infestation, the effect of chronic coccidian infection on individual condition, molt and 12 indices of physiological and immunological function was assessed. We found a significant positive relationship between infestation and heterophil/lymphocyte ratio measured at capture, indicating infectioninduced stress. We also found that coccidians negatively affected feather growth during molt: the increase in wing length of the noninfected birds was significantly higher than that of infected birds. In comparison to control birds, infected birds showed a significantly higher concentration of white blood cells and greater blood bactericidal activity. There was also a positive correlation between infection intensity, agglutination and lysis of blood in the experimentally infested birds, which indicated activation of the constitutive innate immune system during infection. Finally, the total antioxidant capacity of the blood increased significantly, while the carotenoid concentration decreased significantly in infected compared with control birds. Therefore, we showed that coccidians stimulated several measures of the constitutive innate immunity, including the bactericidal activity of the blood, and that coccidians can have significant negative effects on the health and possibly fitness of molting House Sparrows.

Passerine birds, especially during the breeding season and nestling development, are exposed to an array of hematophagous ectoparasites. Although the direct consequences of mite infestation on host fitness and immunological function have been investigated in the Domestic Chicken (Gallus gallus domesticus), parasite-specific immune responses to ectoparasites in passerine species have not been examined in great detail. We investigated the humoral immune response of House Sparrows (Passer domesticus) to hematophagous mite antigens and tested for the presence of mite-specific antibodies in adults, egg yolks, and nestlings in a wild population that was naturally exposed to ectoparasitic mites. Our results showed that adult House Sparrows can mount a specific adaptive immune response against hematophagous mite antigens. Further, we demonstrate that mite-specific antibodies are present in wild House Sparrow populations naturally infested with ectoparasites. The results of this study provide ecological immunologists with a tool for examining host-parasite interactions via a parasite-specific immune assay.

The Hairy Woodpecker (Picoides villosus) has one of the broadest breeding distributions of any North American bird and is also one of the most morphologically variable with as many as 21 described subspecies. This wide distribution and high degree of phenotypic diversity suggests the presence of underlying genetic structure. We used ND2 sequence from 296 individuals from 89 localities throughout the Hairy Woodpecker distribution to address this question and to explore this species' evolutionary history. Phylogenetic analyses identified three main Hairy Woodpecker clades, each ∼1.5% divergent from one another. One clade was comprised of birds from boreal and eastern zones of North America (N&E); the second, of birds from western and southwestern North America (S&W), and the third included only birds from a disjunct population in Costa Rica and Panama. Population genetic analyses and climatic niche models indicated that the N&E and S&W clades have very different recent evolutionary histories. Populations in the N&E are characterized by a lack of genetic structure and a genetic signature of recent population expansion. In contrast, S&W populations are highly structured and relative population stability was inferred. The S&W clade is further structured into three additional geographically and genetically isolated groups: Pacific Coast ranges, interior ranges, and southern Mexico. The continentalscale patterns of genetic variation observed suggest that the complex topography of the montane west has probably been more important than latitude in generating phylogenetic diversity within this species.

Among scolopacid shorebirds, Bar-tailed Godwits (Limosa lapponica) have unusually high intra- and intersexual differences in size and breeding plumage. Despite historical evidence for population structure among Alaska-breeding Bar-tailed Godwits (L. l. baueri), no thorough analysis, or comparison with the population's nonbreeding distribution, has been undertaken. We used live captures, field photography, museum specimens, and individuals tracked from New Zealand to describe geographic variation in size and plumage within the Alaska breeding range. We found a north-south cline in body size in Alaska, in which the smallest individuals of each sex occurred at the highest latitudes. Extent of male breeding plumage (proportion of nonbreeding contour feathers replaced) also increased with latitude, but female breeding plumage was most extensive at mid-latitudes. This population structure was not maintained in the nonbreeding season: morphometrics of captured birds and timing of migratory departures indicated that individuals from a wide range of breeding latitudes occur in each region and site in New Zealand. Links among morphology, phenology, and breeding location suggest the possibility of distinct Alaska breeding populations that mix freely in the nonbreeding season, and also imply that the strongest selection for size occurs in the breeding season.

When to commence breeding is a fundamental decision made by individuals that inhabit seasonal environments. Although photoperiod determines the timing of breeding in most temperate zones, other abiotic conditions can also play a significant role by influencing food availability and, consequently, reproductive performance throughout a breeding cycle. This study used the multibrooded endangered Cape Sable Seaside Sparrow (Ammodramus maritimus mirabilis) to test whether water conditions (rainfall and groundwater levels) influenced breeding variables in a subtropical environment, the Florida Everglades. Timing of breeding was related to rainfall preceding the breeding season, with females initiating nesting up to 1 month earlier in years with greater rainfall. Clutch size averaged 3.4 eggs, and females showed an increase in clutch size as the breeding season progressed and in response to higher groundwater levels during the laying period. This effect was more apparent for first nesting attempts, with drier conditions limiting clutch size. Although wetter conditions favored earlier breeding and larger clutch sizes, annual nest survival (range: 12–36%) was negatively associated with high average rainfall late in the breeding season. Clutch-size variation and high nest survival in Cape Sable Seaside Sparrows' first nesting attempts suggests that food-mediated processes affect their reproductive decisions early in the breeding season, whereas predator-mediated processes drove overall reproductive output, possibly through increased activity of major nest predators during wetter conditions.

Carotenoids can be important antioxidants and immunostimulants for developing embryos and adult birds, and they are often incorporated into colorful sexual displays as signals of individual quality. The allocation of carotenoids to egg yolks and feathers can be affected by a female's physical condition, which can in turn affect offspring growth and survival. We examined relationships between yolk and feather concentrations of carotenoids and various indices of female quality (i.e., body condition, heterophil-to-lymphocyte ratio, hematocrit, date of nest initiation, egg mass, reproductive success) in the Yellow-headed Blackbird (Xanthocephalus xanthocephalus), a brightly colored passerine. Measures of physical condition of female Yellow-headed Blackbirds were correlated with the allocation of carotenoids to both eggs and feathers. Specifically, less stressed (i.e., lower heterophil-to-lymphocyte ratio) females had higher concentrations of β-carotene in their eggs than females that were more stressed. In addition, females with higher hematocrit values (i.e., more red blood cells) had higher concentrations of feather carotenoids. Timing of breeding was also related to variation in yolk carotenoid concentrations; later-breeding females produced eggs with lower concentrations of β-carotene but higher concentrations of lutein, which could be due to renesting or seasonal differences in carotenoid availability and use. Concentrations of yolk and feather carotenoids were not correlated, which suggests that individual carotenoids may have different functions in eggs and plumage. Carotenoid concentrations and female condition variables were not significantly related to the reproductive traits measured, but small sample sizes of females that fledged young may have limited our ability to detect effects. Our results highlight the need for further studies on the condition-dependent allocation and use of carotenoid pigments for reproduction and sexual signals in brightly colored female birds.

Climate change and sea-level rise pose an imminent threat to the survival of coastal ecosystems, but the mechanisms by which animals inhabiting these areas may be affected by these changes are not well studied. During 2007–2009, we quantified the frequency of nest-flooding events at two salt marshes located in the northeastern United States that are of global importance to Saltmarsh Sparrow (Ammodramus caudacutus) conservation. Although nest flooding is a major cause of nest failure in this species, we lack a detailed understanding of exactly how flooding affects success, so it is difficult to determine the magnitude of the threat posed by sea-level rise. We tested whether variables associated with the timing of nest initiation, tide height, and flooding frequency can be used to estimate three aspects of nest fate: the probability of nest success, the probability of nest failure due to flooding, and the number of offspring lost to flooding. Of the 191 nests that we monitored, only 15% were never flooded and 18% were successful; the mean (± SD) number of flooding events observed per nest was 2.8 ± 2.1 (range: 0–10). The top-performing model for each measure of nest fate included variables related to tidal metrics, but model composition for the three measures differed in the importance of particular tide variables. Both tide height and flooding frequency emerged as important drivers of nest fate in this system. Saltmarsh Sparrow nests appear to be extremely vulnerable to even slight increases in sea level.

The influence of heterospecifics on successful avian reproduction remains poorly understood, despite the role that such relationships may play in the evolution of reproductive strategies. We estimated nest survival of Cackling Geese (Branta hutchinsii) near McConnell River, Nunavut, in 2004 and 2005 in relation to (1) nest initiation date; (2) nest age; (3) nesting habitat; (4) presence in or absence from a colony composed mainly of Ross's Geese (Chen rossii); and (5) density of neighboring Lesser Snow Geese (C. caerulescens caerulescens) and Ross's Geese. We also assessed whether there was any consistent pattern in nest densities of Cackling Geese inside and outside the colony, using distance sampling methods that account for imperfect detection. Nest survival declined both with later nesting and with increased densities of surrounding Lesser Snow Geese and Ross's Geese, independently of whether or not Cackling Geese nested in the Ross's Goose colony. However, despite these negative interspecific effects at the neighborhood scale, nests had higher survival probabilities inside the colony than outside it when we controlled for nest initiation date and density of neighboring Lesser Snow Goose and Ross's Goose nests. There was no consistent difference in nest densities of Cackling Geese nesting inside and outside the colony. We conclude that Cackling Geese coincidentally establish nest sites inside the colony; the best nest locations are in low-density areas of the colony, but the location of these areas is unpredictable among years because Ross's Geese usually initiate nests later than Cackling Geese.