Birds of the forest canopy are an integral component of bird communities of neotropical forests but remain largely unstudied, inhibiting any broad characterization of their assemblages. We present the first description of a canopy-bird assemblage from Middle America and, on the basis of > 11000 detections in lowland rainforests in Honduras and Amazonian Brazil, compare two distant canopy-bird assemblages. The richness of canopy birds at the two sites was similar despite the much higher richness of forest birds in Brazil. Furthermore, abundance distributions differed significantly: in Honduras the assemblage was dominated by a small number of superabundant species and had fewer rare species, whereas in Brazil it had fewer abundant species and was thus more even. Omnivores and insectivores dominated the assemblages in terms of species richness, but omnivores were numerically more abundant. Species of forest edges and open habitats, sometimes considered an important component of forestcanopy avifauna, were underrepresented at both sites in comparison to null expectations drawn from the pool of species in each region. Long-distance migrants were more important in Honduras, where they constituted a third of canopy birds, yet species richness of migrants did not differ from a null expectation. Finally, we present a baseline classification of the core constituent species of bird assemblages in the canopy of lowland neotropical rainforests.

The tropical Andes rank first among the world's 25 “hotspots” of biodiversity and endemism yet are threatened and little studied. We contrast population trends in avian diversity in montane cloud forest (bosque altoandino) and similar forest degraded by the planting of introduced tree species (bosque introducido) in the Mazán Reserve, Ecuador. We describe changes in bird diversity and abundance in these habitats over 12 years and evaluate the nature of change within these avian communities. On the basis of 2976 count detections and 419 net captures of 76 species of landbirds, indices of similarity between the habitats were low, with only 47.6% of species occurring in both forest types. From 1994–95 to 2006–07, species richness decreased from 54 to 31 in bosque introducido and from 67 to 30 in bosque altoandino. Capture rates also declined from 56.0 to 28.5 birds per 100 mist-net hr in bosque introducido and from 38.0 to 22.4 birds per 100 mist-net hr in bosque altoandino. We explore various potentially interacting factors that might have caused the observed changes in bird communities, including changes in vegetation within the Mazán Reserve and environmental changes resulting from global warming. But our results also suggest that local and regional changes in habitat outside of the Mazán Reserve were likely responsible for some community changes within the reserve. We argue for increased population monitoring to verify trends and to strengthen the effectiveness of conservation efforts in the Andes.

We studied habitat use of disturbed coastal forest by communities of North American migrant and Cuban resident land birds on Cayo Coco, Cuba. This region is subject to a growing resort industry, yet the ecological effects of this disturbance remain largely unknown. Using mist-nets, we sampled birds during two early winters and one late winter. We sampled at sites adjacent to coastal resorts, and at a distance of up to 5.7 km from resorts, in three habitat types (mixed mangrove, semi-deciduous, and coastal scrub forests). We tested for differences in abundance and richness at sites near and far from resorts and among the three habitat types. We also assessed whether bird distribution was associated with fruit abundance and/or vegetation characteristics. Across seasons, migrants were consistently more abundant at sites near resorts than at sites more distant, whereas richness of Cuban residents was consistently higher at sites near resorts than at those farther away. Neither abundance nor richness of the resident guild varied significantly by habitat. The distributions of neither migrants nor residents were correlated with fruit abundance. High foliage density associated with greater edge habitat provided the strongest explanation for high estimates of abundance and richness of migrants and residents near resorts. Our results suggest that moderately disturbed forests near resorts can support abundant and rich communities of both migrants and residents.

For reproduction, many arctic-nesting migratory birds rely on nutrients obtained on the breeding grounds, so they devote sufficient time to foraging immediately prior to nesting. However, little is known about the increase in foraging effort necessary to meet the energetic requirements of reproduction. In early June 2006 and 2008, we quantified the proportion of time spent foraging before breeding by a large sea duck, the King Eider (Somateria spectabilis), on its breeding grounds in northern Alaska. During >235 hours of behavioral observations, both male and female King Eiders spent >50% of the day loafing (resting, sleeping, comfort behavior, or being alert). Females foraged on average 30% of the time (mean 7.2 hr day^-1,95% CI 6.0-8.4 hr day^-1), three times as much as males (9%; 2.3 hr day^-1, 95% CI 1.5–2.8 hr day^-1). The most common prey in ponds where the eiders foraged were chironomid larvae and worms ranging in length from 1 to 30 mm. If the King Eider's daily energy expenditure on its breeding grounds is similar to values published for related species, it would need to ingest only 0.2–0.6 g dry mass of invertebrates per minute of foraging to meet its energetic requirements. Males did not lose body mass before breeding, and we assume that their foraging effort was sufficient for energy balance. Therefore, female King Eiders appear to triple their foraging effort over maintenance requirements to meet the energetic challenges of egg formation.

Many large birds cannot replace all their flight feathers annually, creating potential life-history tradeoffs between breeding and molting. We show for the Black-footed Albatross (Phoebastria nigripes) that adults with overly worn primary flight feathers suffer reduced fledging success in the current breeding season and are likely to skip the next breeding season, even though they are still alive. If worn flight feathers affect breeding detrimentally, it follows that worn flight feathers accumulate because time for molt is limited. We show that individuals that spend more time breeding replace fewer flight feathers in the following molt. Thus in the Black-footed Albatross incomplete molts link more time invested in breeding to reduced feather quality, and feather quality predicts breeding success in the current season and breeding effort in the following year. Detrimental effects of flightfeather wear on breeding should be expected in other birds that cannot replace all their flight feathers annually. As in other albatrosses, the primaries of the Black-footed Albatross are replaced in an intrinsic molt cycle that in most but not all individuals results in most flight feathers being replaced at least every second year.

Knowledge of the dynamics of long-distance migrations of pelagic seabirds is limited. Recent advances in tracking technology have yielded detailed, continuous accounts of the movements of individual seabirds over large spatial and temporal scales. We studied the timing of migration and year-round distribution of the Westland Petrel (Procellaria westlandica), listed by the IUCN as vulnerable, with miniature archival light loggers (geolocators) deployed on 10 incubating birds breeding in 2007 at Westland, New Zealand. We retrieved data from eight Westland Petrels, indicating the birds migrated in November directly east ∼7000 km from the coast of New Zealand to South American waters in 6 days (range 4–7), then returned the following April in 10 days (range 8–13). The durations of an individual's outward and return flights and the dates of its outward and return migrations were positively correlated. During their journeys east and west, birds spent on average (±SD) 9.9% (±9.7) and 17.2% (±12.0), respectively, of their time on the water. There was also considerable variation in individuals' foraging areas: while breeding, birds used three major coastal areas <1200 km from their colony; during the nonbreeding period, six birds remained off the south coast of Chile, while two others continued their migration through the Drake Passage to waters off southern Argentina. These results expand the known distribution of the species, identify new key foraging areas, and show patterns of outward and return migration behavior consistent in individuals.

The Pelagic Cormorant (Phalacrocorax pelagicus) is the most widespread cormorant in the North Pacific, but little is known about its foraging and diving behavior. However, knowledge of seabirds' foraging behavior is important to understanding their function in the marine environment. In 2006, using GPS dataloggers, we studied the foraging behavior of 14 male Pelagic Cormorants rearing chicks on Middleton Island, Alaska. For foraging, the birds had high fidelity to a small area 8 km north of the colony. Within that area, the cormorants' diving activity was of two distinct kinds—near-surface dives (1–6 m) and benthic dives (28–33 m). Individuals were consistent in the depths of their dives, either mostly shallow or mostly deep. Few showed no depth preference. Dive duration, time at maximum depth, and pauses at the water surface between consecutive dives were shorter for shallow dives than for deep dives. The cormorants made dives of both types throughout the day, but the frequency of deep dives increased toward evening. Maximum foraging range was 9 km; maximum total distance traveled per trip was 43.4 km. Trip durations ranged from 0.3 to 7.7 hr. Maximum depth of a dive was 42.2 m, and duration of dives ranged from 4 to 120 sec. We found that Pelagic Cormorants at Middleton Island were faithful to one particular foraging area and individuals dived in distinct patterns. Distinct, specialized foraging behavior may be advantageous in reducing intra- and interspecific competition but may also render the species vulnerable to changing environmental conditions.

From 1995 to 1998, we tracked movements of adult Swainson's Hawks (Buteo swainsoni), using satellite telemetry to characterize migration, important stopover areas, and movements in the austral summer. We tagged 46 hawks from July to September on their nesting grounds in seven U.S. states and two Canadian provinces. Swainson's Hawks followed three basic routes south on a broad front, converged along the east coast of central Mexico, and followed a concentrated corridor to a communal area in central Argentina for the austral summer. North of 20° N, southward and northward tracks differed little for individuals from east of the continental divide but differed greatly (up to 1700 km) for individuals from west of the continental divide. Hawks left the breeding grounds mid-August to mid-October; departure dates did not differ by location, year, or sex. Southbound migration lasted 42 to 98 days, northbound migration 51 to 82 days. Southbound, 36% of the Swainson's Hawks departed the nesting grounds nearly 3 weeks earlier than the other radio-marked hawks and made stopovers 9.0–26.0 days long in seven separate areas, mainly in the southern Great Plains, southern Arizona and New Mexico, and north-central Mexico. The birds stayed in their nonbreeding range for 76 to 128 days. All used a core area in central Argentina within 23% of the 738 800-km² austral summer range, where they frequently moved long distances (up to 1600 km). Conservation of Swainson's Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons, including migration stopovers.

Examining incubation behavior during laying and that behavior's consequences on patterns of hatching can help discriminate among hypotheses competing to explain the evolution of asynchronous hatching. Consequently, I documented nest attentiveness and patterns of hatching of American Coots (Fulica americana) nesting in southwestern Manitoba from 1986 to 1991. Coots gradually increased their nest attentiveness from laying of the first to the sixth egg, and attentiveness to late-season clutches peaked earlier during laying, but it was unaffected by clutch size, first vs. replacement nest, or supplemental food. Nest attentiveness during laying was effective at initiating embryo development, as evidenced by a strong positive correlation between the order of laying of eggs and order of hatching of chicks. These results are most consistent with hypotheses that nest attentiveness during laying evolved to protect eggs or maintain viability of embryos. Clutch-initiation date had the most pronounced effect on patterns of hatching, with late-laid clutches hatching sooner and more asynchronously. Very large clutches took longer to hatch, whereas renesting and supplementally fed coots hatched early-sequence eggs more quickly. Despite large clutches and pronounced asynchrony, there was no evidence that neglect of last-laid eggs delayed their hatching. Observed variation in patterns of hatching provided little support for hypotheses that asynchrony of hatching has evolved to produce a hierarchy within a brood (e.g., brood reduction, reduction of peak loads) but strongly supported hypotheses that hatching asynchrony serves to minimize risks to unincubated eggs (e.g., egg viability, nest protection, and nest failure).

For a single lineage of birds, the diversity of mating systems and parental care among shorebirds (Charadrii) is high, which has made them an important group for investigations of the evolution of social mating systems. From 2003 to 2007, we studied a population of the Upland Sandpiper (Bartramia longicauda) at Konza Prairie Biological Station in northeastern Kansas. Our objectives were to determine the genetic mating system of this socially monogamous shorebird and to determine whether spatial patterns of philopatry and nest placement might affect opportunities for extra-pair mating. We used six microsatellite markers to estimate rates of extra-pair paternity in 58 family groups (107 parents, 184 offspring). We found that 30% of broods contained extra-pair offspring, representing 15% of chicks, the highest rate of extra-pair paternity ever reported in a socially monogamous shorebird. High rates of extra-pair paternity were not due to the degree of relatedness between partners in mated pairs, and they did not result in greater diversity among broods with extra-pair young. We used a spatial genetic-autocorrelation analysis and found evidence for relatedness among females nesting <1 km apart. The Upland Sandpiper might have a high rate of extra-pair paternity because related females nest synchronously and in close proximity, but the probability of extra-pair young was not related to nest density or distance to nearest nest. Female-biased natal philopatry is unusual among birds but is consistent with the mate-defense mating system of the Upland Sandpiper.

Making a detour can be advantageous to a migrating bird if fuel-deposition rates at stopover sites along the detour are considerably higher than at stopover sites along a more direct route. One example of an extensive migratory detour is that of the Sharp-tailed Sandpiper (Calidris acuminata), of which large numbers of juveniles are found during fall migration in western Alaska. These birds take a detour of 1500–3400 km from the most direct route between their natal range in northeastern Siberia and nonbreeding areas in Australia. We studied the autumnal fueling rates and fuel loads of 357 Sharp-tailed Sandpipers captured in western Alaska. In early September the birds increased in mass at a rate of only 0.5% of lean body mass day^-1. Later in September, the rate of mass increase was about 6% of lean body mass day^-1, among the highest values found among similar-sized shorebirds around the world. Some individuals more than doubled their body mass because of fuel deposition, allowing nonstop flight of between 7100 and 9800 km, presumably including a trans-oceanic flight to the southern hemisphere. Our observations indicated that predator attacks were rare in our study area, adding another potential benefit of the detour. We conclude that the most likely reason for the Alaskan detour is that it allows juvenile Sharp-tailed Sandpipers to put on large fuel stores at exceptionally high rates.

At night during the breeding season, Xantus's Murrelets (Synthliboramphus hypoleucus) congregate on the water adjacent to nesting colonies. We examined relationships of attendance at these nocturnal congregations, breeding status, and daytime foraging locations of radio-marked Xantus's Murrelets from Anacapa Island (33 in 2002, 44 in 2003) and Santa Barbara Island (35 in 2002) in the California Channel Islands. Murrelets that spent more nights attending congregations were located closer to the island during the day, so regular attendance at the congregations may have constrained daytime traveling distances to foraging locations. In mid-May 2003 home-range sizes increased while congregation attendance decreased, likely indicating the end of colony attendance and declining availability of prey near Anacapa Island. In both years, incubating murrelets foraged farther from the colony than did nonbreeding murrelets, suggesting that breeding and nonbreeding murrelets use different foraging strategies to meet their energetic requirements.

Determining factors that affect post-fledging dispersal and survival is key toward a better understanding of the population dynamics of species with a propensity for range expansion, such as the Eurasian Collared-Dove (Streptopelia decaocto). By radio tracking, we assessed the survival, causes of mortality, movements, and emigration of 41 juvenile Eurasian Collared-Doves, monitored in two villages from a fragmented urban and agricultural landscape in western France, 2001–2002. Thirteen weeks after fledging the doves' survival was 61% (±8% SE), and predation was the leading cause of mortality. Home ranges and distances traveled increased over time. Individuals in better body condition had larger home ranges and a higher propensity to emigrate. In addition, those originating from the smaller village had smaller home ranges and were more likely to emigrate. Our results suggest that range expansion of the Eurasian Collared-Doves should be faster in regions where urban areas are smaller but more closely spaced.

We used an information-theoretical approach and Cormack—Jolly—Seber models for open populations in program MARK to examine relationships between survival rates of Northern Spotted Owls and a variety of local weather variables and long-term climate variables. In four of the six populations examined, survival was positively associated with wetter than normal conditions during the growing season or high summer temperatures. At the three study areas located at the highest elevations, survival was positively associated with winter temperature but also had a negative or quadratic relation with the number of storms and winter precipitation. A meta-analysis of all six areas combined indicated that annual survival was most strongly associated with phase shifts in the Southern Oscillation and Pacific Decadal Oscillation, which reflect large-scale temperature and precipitation patterns in this region. Climate accounted for a variable amount (1–41%) of the total process variation in annual survival but for more year-to-year variation (3–66%) than did spatial variation among owl territories (0–7%). Negative associations between survival and cold, wet winters and nesting seasons were similar to those found in other studies of the Spotted Owl. The relationships between survival and growing-season precipitation and regional climate patterns, however, had not been reported for this species previously. Climate-change models for the first half of the 21st century predict warmer, wetter winters and hotter, drier summers for the Pacific Northwest. Our results indicate that these conditions could decrease Spotted Owl survival in some areas.

The Mexican Sheartail (Doricha eliza) is a hummingbird endemic to Mexico, where it occurs in disjunct populations in the states of Yucatan and Veracruz. In neither area has the species' reproductive biology been studied. On the basis of observations in Veracruz we characterize the species' eggs (the first description for the genus), fledging success, nestling growth, causes of mortality, nest-site selection, and courtship behavior. We located 11 active nests at various stages (8 eggs and 12 chicks, so not all nests contributed to all data sets). Nests were placed on four species of plants (three of them with spines), and some were aggregated. The species nested in natural grasslands and cattle pastures dominated by Acacia. Males formed leks. Chicks fledged from 4 of 11 nests, yielding 8 juveniles from 22 possible. Causes of mortality were predation, weather, human disturbance, and failure to hatch. Conservation of nesting sites in Veracruz is necessary for maintaining a healthy population.

Riparian woodlands of aspen (Populus tremuloides) provide valuable breeding habitat for several cavity-nesting birds. Although anecdotal information for this habitat is available for Lewis's Woodpecker (Melanerpes lewis), no study has previously examined the importance of aspen woodlands to this species' breeding biology. From 2002 to 2004, we monitored 76 Lewis's Woodpecker nests in aspen riparian woodlands of south-central Idaho to describe nest-site characteristics and estimate the nests' survival. We quantified the vegetation at nest sites and randomly selected other sites to determine habitat features important in the species' selection of a nest site. We then related these features, as well as several time-specific covariates, to nest survival. Lewis's Woodpecker selected nest trees that were larger in diameter than random trees and selected nest sites with more trees, fewer woody stems, and less bare ground than random sites. However, nest-site characteristics were not important determinants of nest survival. Rather, nest-initiation date and daily maximum temperature had the strongest influence on nest survival, which was higher for early nesters and increased with increasing daily maximum temperature. Nest survival (74%) and productivity (2.3 fledglings per successful nest) were comparable to values observed for Lewis's Woodpeckers in burned pine forests, suggesting that aspen riparian woodlands also serve as valuable breeding habitat for this species in the Intermountain West.

We investigated how variation in the timing and amount of annual precipitation influenced annual variation in the fecundity of the Spotted Antbird (Hylophylax naevioides) in central Panama from 1998 to 2001. The onset of nesting varied significantly by year and corresponded with a notably strong episode of El Niño—Southern Oscillation that generated variation by year in dry-season precipitation and the onset of wet-season rains. The end of nesting, however, was not influenced by annual variation in rainfall. Fecundity was also similar each year despite pronounced variation in wet-season precipitation. Although breeding pairs attempted an average of almost five nests per year, slightly less than one nest attempt per pair was successful. Annual fecundity was 1.5 fledglings per pair, exceeding the turnover of territorial adults in this population. Extended parental investment in care of fledglings delayed renesting and consequently limited subsequent opportunities to breed within the season. Predation and duration of parental care likely influence annual fecundity more than variation in environmental conditions.

We studied environmental and maternal factors explaining bacterial loads on eggshells in a population of a hole-nesting passerine, the Pied Flycatcher (Ficedula hypoleuca) and the possible effects of bacteria on hatching success. We collected bacteria from eggshells at early and late stages of incubation and from females' feces, as a surrogate for cloacal samples, at intermediate stages of incubation. Higher environmental temperatures during laying promoted bacterial loads on the eggshells during early incubation, supporting the fact that bacterial growth is generally favored by increasing ambient temperature. Bacterial loads on the eggshells at late stages of incubation were correlated positively with bacterial loads in the female's cloaca, suggesting possible vertical transmission of bacteria. We detected no significant differences between bacterial loads of the eggshells at early and late stages of incubation. Possible bacteriostatic effects of incubation and/or other alternative mechanisms not associated with incubation may be responsible for this pattern. Bacterial loads seemed not to affect hatching success, raising the question whether bacterial species composition rather than bacterial load affects embryo survival.

Animals select habitat to satisfy life-history requirements, yet few habitat-selection studies consider multiple factors, especially food. Because resources vary in abundance and quality across different spatial scales or habitat types, selected habitat features may also vary, making habitat selection incongruent. Using an information-theoretical approach, we assessed whether Phainopeplas (Phainopepla nitens) select breeding habitat for food abundance or vegetation structure at nest-tree and nest-patch scales in two woodland types, acacia and mesquite, in the Mojave Desert. Habitat selection at the tree and patch scales was congruent: models containing both food (mistletoe) and structure variables had stronger support than models with only food or structure variables. In both woodland types, nest trees were larger and had more food, and in nest patches food abundance, tree density, tree height, and cover were greater than in non-nest patches. However, nests in acacia were higher than those in mesquite, acacia nest trees were smaller and had more food but less cover, and acacia nest patches had lower tree density and more food. These differences between woodland types apparently led to incongruence in nest-site selection: the difference between height of nest and non-nest trees was greater in shorter acacia than in mesquite woodlands, and the difference in food abundance between nest and non-nest sites was greater in food-poor mesquite woodlands. Contrary to assertions that vegetation structure drives nest-site selection, Phainopeplas' nest-site selection reflects both food abundance and vegetation structure at all spatial scales, underscoring the importance of multiple factors, scales, and habitats to habitat-selection studies.

Researchers commonly model nest density as a function of ecological variables, but nests, like birds, can be undetected while present. In the Nebraska Sandhills in 2007, we used the rope-drag method on previously located Western Meadowlark (Sturnella neglecta) nests to model nest-detection error and nest density. Detecting nests by rope dragging (commonly used for nests of grassland birds) is conditional on two primary sources of nest availability, adults attending nests and adults flushing from nests in response to disturbance from the rope, the behavioral cue necessary for nest detection. On the basis of our trials with rope dragging, the probability of adults attending nests was 0.46. The probability of trials eliciting flight responses from adults was 0.19, indicating that observed estimates of nest density were subject to detection error and negatively biased. We compared our ability to detect differences in nest densities between two habitat types with a statistical power analysis, using (1) t-tests with estimates of apparent, uncorrected density and (2) a Bayesian hierarchical model incorporating nest-detection error. Our power analysis indicates that accounting for detection error in a hierarchical model increased statistical power for revealing differences in nest densities by habitat type. We discuss mechanisms underlying detection error for nests of grassland birds and make recommendations for sampling and modeling to maximize the reality of models for nest detectability and density.

From 2001 to 2008, we estimated probabilities of survival and encounter of adult House Finches (Carpodacus mexicanus) breeding at Stone Lakes National Wildlife Refuge, Sacramento County, California, from capture-recapture data on birds trapped with mist nets and ground traps. Our primary objectives were to determine when West Nile virus (WNV, Flaviviridae, Flavivirus) arrived at the site and if survivorship changed after this arrival. We monitored viral activity by screening blood samples from House Finches for WNV antibodies with an enzyme immunoassay and by testing mosquito pools for viral RNA. WNV arrived after the breeding season in late 2004, so we compared data from 2001–2004 (pre-WNV) to that from 2005–2008 (post-WNV). We found a decrease in annual survival following the arrival of WNV (pre-WNV, 0.59; post WNV, 0.47), which, if representative, may have contributed to the reported decline in the abundance of this species in northern California.