Documenting bird—habitat relationships by statistical modeling has been a cornerstone of avian ecology for decades, but rarely is the predictive capacity of such models tested. To evaluate how well quantitative models of habitat relationships developed during an initial survey period predicted species distributions and/or abundances in a later period, in 1997 we revisited 13 shrubsteppe sites that we had previously surveyed from 1977 through 1983. Using multiple regression (linear and logistic) and classification and regression trees (CART), we developed habitat models for each species based on the “historic” period. R² values for these models ranged from 0.45 to >0.95. We then predicted bird species distributions and abundances by using the 1997 habitat attributes as inputs for the models derived from the earlier data. These models generally failed to predict 1997 bird distributions and abundances accurately; only 1 of 14 multiple regressions and 2 of 14 CARTs explained a statistically significant amount of variation in the target species. Thus, although the models may capture relationships between a species and environmental variables when aggregated over multiple years, they may not adequately predict the subsequent distribution and abundance of populations over shorter time scales. This result may limit the usefulness of multivariate habitat models in resource management.

Surveys based on double sampling include a correction for the probability of detection by assuming complete enumeration of birds in an intensively surveyed subsample of plots. To evaluate this assumption, we calculated the probability of detecting active shorebird nests by using information from observers who searched the same plots independently. Our results demonstrate that this probability varies substantially by species and stage of the nesting cycle but less by site or density of nests. Among the species we studied, the estimated single-visit probability of nest detection during the incubation period varied from 0.21 for the White-rumped Sandpiper (Calidris fuscicollis), the most difficult species to detect, to 0.64 for the Western Sandpiper (Calidris mauri), the most easily detected species, with a mean across species of 0.46. We used these detection probabilities to predict the fraction of persistent nests found over repeated nest searches. For a species with the mean value for detectability, the detection rate exceeded 0.85 after four visits. This level of nest detection was exceeded in only three visits for the Western Sandpiper, but six to nine visits were required for the White-rumped Sandpiper, depending on the type of survey employed. Our results suggest that the double-sampling method's requirement of nearly complete counts of birds in the intensively surveyed plots is likely to be met for birds with nests that survive over several visits of nest searching. Individuals with nests that fail quickly or individuals that do not breed can be detected with high probability only if territorial behavior is used to identify likely nesting pairs.

In some seabirds sexually dimorphic in size, males and females segregate at sea or diverge in other aspects of foraging behavior. We examined factors influencing foraging strategies of Cory's Shearwater and compared the sexes' flight morphology and activity patterns. Trip duration, incubation-shift length, total mass gain, and rate of mass gain at sea of birds from our two study colonies differed. The colonies are situated in regions of contrasting oceanographic conditions: Selvagem Grande, a remote subtropical oceanic island, and Berlengas, an island on the Portuguese continental shelf. Although the wing loading and wing span of males and females breeding at Selvagem Grande differed significantly, sex did not consistently influence activity patterns of Cory's Shearwaters foraging at sea during the incubation period. Moreover, both sexes breeding at Selvagem Grande foraged in areas with similar sea-surface temperatures. Our study suggests that sexual differences in size and shape may be poor predictors of differentiation in the ways male and female pelagic seabirds use the marine environment.

In long-lived species, juvenile survival and the age at which individuals begin the process of recruitment have important consequences for individual fitness and population growth. We investigated how characteristics of fledglings (mass, wing length, and date) influenced the local survival of juveniles and age at first return to the natal breeding colony of two annual cohorts of the Tufted Puffin (Fratercula cirrhata) at Triangle Island, British Columbia. Although both cohorts were produced in years when nestlings grew quickly and had high mass at fledging, only 8% of banded nestlings from the 1999 cohort, but 43% of nestlings from the 2000 cohort, were resighted up to 2008. Age at first return of the 2000 cohort averaged one year younger than that of the 1999 cohort. In addition to the cohort effect, we found that the local survival of juveniles increased strongly with wing length at fledging, providing an ultimate explanation for puffin nestlings' preferential allocation of energy and nutrients to wing growth over mass growth. Mass and date at fledging had detectable, but much weaker, effects on survival. Conversely, nestlings' age at first return decreased strongly with mass at fledging, weakly with wing length at fledging. Ours is the first study to report an effect of characteristics at fledging on juvenile survival and age at first return in an alcid whose offspring receive no parental care after they leave the nest site.

The Red-bellied Woodpecker species group (Melanerpes carolinus and relatives) is composed of five morphologically similar species whose limits have been unclear. The relationship of the Golden-fronted Woodpecker (M. aurifrons) to the remainder of the group is particularly uncertain. We used mitochondrial DNA sequences to examine the phylogeny of this group and its close relatives. We sequenced 872 bp, including fragments of the genes for ND2, ND3, COIII, and tRNAmet, of 11 species of Melanerpes. We constructed trees from combined sequences by using the maximum likelihood and Bayesian inference approaches. We found that M. aurifrons is not monophyletic but rather consists of two clades, one comprising tropical populations (M. santacruzi), the other, consisting of northern populations, being sister to M. carolinus. The Caribbean species, M. superciliaris, is sister to the carolinus—aurifrons clade. The group as a whole appears to have diversified into multiple lineages in response to several episodes of vicariance, perhaps associated with glacial—interglacial cycles. As a result of these findings, major taxonomic changes in the group are needed.

Among lek-breeding manakins (Pipridae), courtship repertoires are extremely diverse and have played a central role in establishing phylogenetic relationships within the family. Behaviorally, Lepidothrix is among the least known genera in the family, with brief accounts published for only two of the eight species. Here, I describe the lek structure, territory characteristics, vocalizations and behavioral display elements of the Blue-crowned Manakin (Lepidothrix coronata coronata) in eastern Ecuador. From 2003 to 2006, I located all leks in two 100-ha study plots (average of 13.5 leks 100 ha^-1) and recorded behavior at individual territories in ten leks. Males displayed solitarily or at exploded leks with up to seven individual territories of ∼0.1 ha; within a lek, territory centers were separated by about 90 m. Males in definitive and predefinitive plumage (2 years and older) held stable territories, whereas first-year, female-plumaged males did not hold stable territories but sometimes associated loosely with territorial males. I noted 4 vocalizations and 11 male display behaviors during solitary and group displays involving other males and females, revealing a repertoire considerably more diverse than previously documented.

Secondary-cavity-nesting birds occur widely throughout the world, but little information is available on the benefits of the nest's microclimate for such species, particularly for those using natural cavities. We investigated the influences of microclimate on a threatened secondary-cavity-nesting passerine, the South Island Saddleback (Philesturnus carunculatus carunculatus). Our aims were to determine whether (1) saddlebacks select tree cavities with microclimates less variable than those of other tree cavities in their surrounding territory, (2) whether structural aspects of tree cavities translate into certain microclimate characteristics, and (3) if less frequently used sites not in tree cavities (e.g., cavities in banks or in vegetation) have thermal properties similar to those of tree-cavity nests. We found that the saddleback's tree-cavity nests were more stable in temperature, more insulated against cold, and did not change temperature as rapidly as the ambient air or unused tree cavities. Regression analysis showed that of structural characteristics of tree cavities examined, only one, entrance width, was significantly associated with an aspect of microclimate (minimum temperature). Additionally, we found that regardless of cavity type the thermal properties of saddleback nest cavities were similar. These results indicate that saddlebacks likely select nest cavities with less variable thermal properties that are potentially beneficial, and future studies experimentally manipulating the variability of microclimate may be fruitful in determining the effect of microclimate on reproductive success. Nevertheless, this study is one of the first to demonstrate microclimate as a factor determining selection of natural nest cavities over available unused cavities.

Understanding how genetic variation in the Tree Swallow (Tachycineta bicolor) is geographically structured is informative because this broadly distributed North American bird is increasingly used as a model for studies of mating systems, life-history traits, and physiology. We explored patterns of phylogeographic differentiation across the Tree Swallow's breeding range by using nine microsatellite loci and a mitochondrial DNA sequence marker. Contrary to this species' high population-level variation in life-history traits and other ecologically important characteristics, we found no genetic structuring across the majority of its distribution, spanning Tennessee, New York, and Alaska, but we found that birds from California form a distinct yet subtly differentiated genetic cluster. The Tree Swallow can be characterized as a species with both continent-wide genetic panmixia and slight differentiation at one edge of its breeding distribution. This pattern of genetic variation has implications for understanding the underlying basis of geographic variation in this species' life history and other phenotypic traits.

Altricial young face two significant energetic challenges in the nest: thermoregulation and stress caused by ectoparasites. Ectoparasites feed on blood of nestlings and serve as vectors for bacterial and viral infections. Many bird species line their nests with feathers, which insulate the nest and reduce heat loss from chicks. Feathers may also affect ectoparasite numbers by serving as a parasite barrier. We tested the possible roles of nest feathers and the effects of nest parasites on the growth and survival of Tree Swallow (Tachycineta bicolor) nestlings by comparing young in control nests with those in nests from which we removed feathers and removed feathers plus used an insecticide in an attempt to reduce ecotoparasites. On the day chicks fledged, control nests had seven times more feathers in them than both categories of nests from which we removed feathers. Nestlings in control nests were larger than those in nests from which feathers were removed, and chick growth was positively related to number of feathers in the nest. Among the three categories, however, time between hatching and fledging and number of chicks fledged did not differ. Time between hatching and fledging may have been influenced by amount of rain just prior to fledging. The abundance and composition of arthropods in the nest did not differ among the categories either, suggesting that our treatments did not significantly reduce parasite numbers. Therefore, the effect of parasites on chick growth and survival remains equivocal. We concluded that feathers did not serve as an ectoparasite barrier, though they affected nestlings' growth rates positively.

Mist netting is widely used to monitor the reproductive success of passerines, yet little is known about its effects on bird ecology. Using a 25-year data set from central California, we evaluated the effects of constant-effort mist netting on the reproductive performance of the Wrentit (Chamaea fasciata) and Song Sparrow (Melospiza melodia). We compared nest survival, number of young fledged, and an index of nestling condition (mass corrected for body size) at nests where at least one parent was captured while the nest was active to these variables at nests where neither parent was captured. We also compared these characteristics for nests at varying distances from nets run at different frequencies. Wrentit nestlings from nests closer to less frequently run nets were in poorer condition than those from nests close to more frequently run nets and than those far away from any nets. For the Song Sparrow, daily nest survival was higher where at least one parent was captured while the nest was active. For all other comparisons, there was no statistical evidence that mist netting had an effect on reproductive performance of these species. This information should ease concerns about the use of mist nets in monitoring avian demographics.

Maximizing reproductive output often entails a trade-off between energy spent on current breeding attempts and that saved for future reproductive opportunities. For species with biparental care, energy spent on the current breeding attempt represents not only a trade-off with future breeding opportunities but also an interaction with the energetic effort of one's mate. In most songbird species, the female typically invests the most in the early stages of breeding. Consequently, the male's contribution to provisioning young may free the female from this energetically costly activity and aid her ability to attempt a second brood. We investigated parental provisioning in the Black-throated Blue Warbler (Dendroica caerulescens) to see if males and females altered their provisioning rates with respect to first and second broods. Using parental provisioning rates from 239 nests from three study sites over 6 years, we show that females provisioned young of first broods at a rate lower than that for second broods, while males' provisioning rate did not differ. Males' provisioning rate was inversely associated with that of females, with males increasing their provisioning when the number of young in a nest increased while females' provisioning decreased. Consequently, we believe our results highlight both the trade-off in energy females spend on current and future reproduction and the role of males' care in helping to maintain reproductive output through increased effort when conditions for feeding are difficult.

Altricial nestlings encase excrement in fecal sacs that parents remove by either ingesting them or transporting them away from the nest. Ingestion may allow energetically or nutritionally deprived parents to recapture energy or nutrients that might be lost because of nestlings' inefficient digestion (the “parental-nutrition hypothesis”), but ingestion may also permit parents to avoid flights from the nest that interfere with parental care (e.g., brooding young; the “economic-disposal hypothesis”). We used a hypothetico-deductive approach to test the two hypotheses' ability to account for fecal-sac ingestion by the Spotted Towhee (Pipilo maculatus). We confirmed the parental-nutrition hypothesis' predictions that more fecal sacs should be ingested in years of food shortage (males only), late in the season when food supplies decline (both sexes), by parents that had the greatest difficulty raising young (i.e., underweight young), and that adults' body condition should vary directly with their rate of fecal-sac ingestion (females only). We rejected the economic-disposal hypothesis' prediction of a decline in fecal-sac ingestion with increasing brood size. The latter, plus the observation that nearly 40% of males ingest fecal sacs despite their spending virtually no time attending nests, suggests that fecal-sac ingestion is not a mechanism to avoid needless and time-consuming flights from the nest that interfere with parental care. Fecal-sac ingestion by Spotted Towhees is better interpreted as either a resource supplement to parents or as a mechanism to satiate hunger so that parents can maintain rates of feeding to dependent young.

Grassland-obligate birds are undergoing some of the steepest population declines of all North American passerines. Few studies have addressed these species' patterns of habitat use in their winter ranges in the southeastern United States. The dry prairie of south-central Florida constitutes one of the largest areas of contiguous grassland remaining within this region and during winter supports a diverse group of migratory grassland-obligate birds. Modern land-use of this region has altered the ecosystem's natural fire regimes and shifted the vegetative community away from graminoids and forbs toward overabundance of woody-stemmed species such as the saw palmetto (Sereona repens). Simultaneously, the prairie's historic range has decreased with urban development and conversion to agriculture. In order to understand how these changes affect overwintering grassland birds, we documented the dry prairie's winter bird community and evaluated the effects of habitat characteristics and time since fire on the occurrence of the Grasshopper Sparrow (Ammodramus savannarum pratensis) and Sedge Wren (Cistothorus platensis), two winter residents. We surveyed birds via flush transects and used an information-theoretic approach to select models that best predicted the species' occurrence. Time since fire was the best predictor of the Grasshopper Sparrow both years of our study, and occupancy by the Grasshopper Sparrow was six times more likely if transects were burned within the previous year. The Sedge Wren favored longer intervals between fires, and its response to habitat covariates in the two years differed. These results highlight the need for dry prairie to be managed with natural (1–3 years) fire-return intervals to maintain wintering habitat for declining grassland birds.

The role of both temporal and spatial variability in nest predation and food availability in influencing birds' decisions about clutch size has not been studied. I examine patterns in nest-predation risk and food availability across a range of severity of wildfire to investigate their relationship to clutch size in the Dark-eyed Junco (Junco hyemalis), which breeds commonly in burned forests. Spatial variation in burn severity led to lower risk of nest predation in patches of intermediate severity in the first two years after the fire, while food availability was inversely related to burn severity during only the first year post-fire. Spatial variation in risk of nest predation explained variation in clutch size only during the first year post-fire when food was limited, consistent with parents investing less in risky nest locations during periods of nutritional stress. Nest-predation risk increased seasonally during both year 1 and year 2 post-fire. Clutch size rose dramatically over the first breeding season post-fire, paralleling a unique seasonal increase in food availability in year 1, consistent with juncos tracking temporal variation in food availability by investing more in eggs. Results are consistent with parents balancing spatio-temporal variation in resource limitation with predation risk in their investment in eggs. Disagreement between existing studies as to the relative importance of food and nest predation further highlights the need for carefully designed experimental approaches that integrate explanations for both temporal and spatial trends in sources of selection likely to shape the evolution of clutch-size decisions.

Invasive species are often implicated in population declines of native species because of predation. The red imported fire ant (Solenopsis invicta) has been documented to prey on songbird nests. We conducted a replicated manipulative experiment to determine the decrease in nest survival caused by S. invicta. In 2006 and 2007 we monitored 71 nests, 44 of the White-eyed Vireo (Vireo griseus) and 27 of the Black-capped Vireo (V. atricapilla), in nine patches of 36–103 ha each in central Texas. We prevented S. invicta from preying on nests by applying insect-specific chemical and physical barriers at individual nests. Excluding S. invicta increased nest survival from 10% to 31% for the White-eyed Vireo and from 7% to 13% for the Black-capped Vireo. Our results suggest the decrease in nest survival of songbirds susceptible to predation by S. invicta may be substantial in the areas this ant occupies.

In 2003, we evaluated nest survival and density of the Dickcissel (Spiza americana), Eastern Meadowlark (Sturnella magna), Field Sparrow (Spizella pusilla), and Red-winged Blackbird (Agelaius phoeniceus) in four unhayed, two earlyhayed (26–31 May) and three late-hayed (17–25 June) fields in northwestern Arkansas. Rope dragging and observations revealed 89 nests. Daily nest-survival rates (SE) prior to haying ranged from 0.94 (0.03) to 0.97 (0.02). Early haying affected both nest-survival rates and bird densities negatively, whereas late haying had minimal effects. Fifteen nests in hayed portions of early-hayed fields were destroyed, whereas only 2 of 52 nests were affected by late haying. Density was at least 0.98 birds ha^-1 higher in unhayed than in early-hayed fields and 1.03 birds ha^-1 higher in late-hayed than in early-hayed fields. In northwestern Arkansas, postponing haying until mid- to late June would allow time for nestlings to fledge, would have little effect on bird densities, and would affect hay nutrition and regrowth minimally.

The Humboldt (Spheniscus humboldti) and Magellanic (S. magellanicus) Penguins overlap over 1100 km along the coast of the southeastern Pacific Ocean, and much has been hypothesized about hybridization between them. We visited Puñihuil and Metalqui islands, southern Chile (41–42° S), where both species form mixed colonies; these are also the Humboldt Penguin's southernmost colonies. We observed one mixed pair attending chicks and two adults of intermediate color pattern, one of which tended a chick at a nest. Additionally, on the basis of analysis of 30 blood samples of Humboldt Penguins from the Puñihuil colony, we report the first documented Humboldt × Magellanic Penguin hybrid. Judged from the pattern of restriction fragments, this bird had a Magellanic dam and a Humboldt sire. We sequenced mitochondrial and nuclear copies independently to confirm these results. We suggest that hybridization at Metalqui and Puñihuil is encouraged by the low abundance of the Humboldt Penguin rather than by failed mate recognition.

Birds that nest along reservoir or river shorelines may face fluctuating water levels that threaten nest survival. On Lake Sakakawea of the upper Missouri River, 37 and 70% of Piping Plover (Charadrius melodus) nests found in 2007 and 2008, respectively, were initiated at elevations inundated prior to projected hatch date. We describe eight events at seven nests in which adult Piping Plovers appeared to have moved active nests threatened by rising water or gathered eggs apparently displaced by rising water on Lake Sakakawea and the Garrison reach of the upper Missouri River. Additionally, we describe one nest that was moved after the habitat at the nest site had been disturbed by domestic cattle. Our observations and evidence indicate that adult Piping Plovers are capable of moving eggs and establishing nests at new sites during incubation. Furthermore, our results suggest that Piping Plovers evaluate their reproductive investment under potential threat of nest loss and may be capable of acting prospectively (moving nests prior to inundation) and reactively (regathering eggs after inundation) to avoid nest failure.

The distribution of the Florida Burrowing Owl (Athene cunicularia floridana) has expanded from primarily rural areas in south-central Florida to include urban/suburban areas to the north, northwest, south, and southeast. While Florida Burrowing Owls still reside in rural areas, the majority of previous research and current management strategies focus on urban/ suburban populations. Determining differences in the owl's ecology between rural and urban/suburban areas can aid in creating effective statewide management strategies for this species. We compared the available prey and diet of Burrowing Owls in a rural and urban environment. Although, on the basis of analysis of pellets, insects and arachnids were the two most frequent food items at both the rural and urban sites, the diets at the two sites differed, largely because of greater consumption of avian prey in the urban habitat. This study is the first comparison of dietary and prey-availability differences between rural and urban Burrowing Owl populations.

The dawn chorus is a collective behavior involving a network of birds signaling at the same time. Two hypotheses can explain the mechanisms of dawn singing. The “condition-dependent hypothesis” states that the dawn chorus consists of a “broadcast network” in which the signal is given in all directions but is not dependent on the singer's neighbors' chorus. The song output is condition dependent and can thus be limited by the amount of food to which a signaler has access to in its territory. On the other hand, the “social-dynamic hypothesis” states that during the chorus the birds are constantly interacting with their neighbors. Under this scenario, the dawn chorus consists of an “interactive network” and the song output is not dependent on the condition of the signaler but on the interaction with the neighbors. To determine which scenario best explains the mechanisms of the dawn chorus in the Black-capped Chickadee (Poecile atricapillus), we set up a supplemental-feeding experiment in a dyadic fashion by providing 3.5 g of mealworms to selected birds and compared their song output to that of unfed counterparts by controlling for rank and habitat. We found that fed birds, both dominant and subordinate males, sang more than unfed birds. We thus conclude that body condition is a critical variable contributing to individual differences in song output in the Black-capped Chickadee and consequently the functioning of the dawn-chorus network.

Many studies have demonstrated the deleterious effects of introduced predators on resident populations of island birds, but few have quantified their effect on the survival and space-use behavior of migratory species. We used radio telemetry to investigate the winter survival and roosting patterns of Bicknell's Thrush (Catharus bicknelli) at two sites in the Dominican Republic. Depredation by introduced rats was the only cause of mortality among 53 radio-tagged individuals monitored between January and March over multiple years; five (9%) marked individuals were depredated. Predator trapping revealed the presence of both the black rat (Rattus rattus) and Norway rat (R. norvegicus) and that the density of rats was higher in broadleaf cloud forest than in nearby pine forest. Some thrushes that used cloud forest exclusively during the day roosted at night in adjacent pine habitat. We suggest that introduced rats exert predation pressure on wintering Bicknell's Thrush in the Dominican Republic and that nocturnal arboreal rat predation could influence the thrush's space-use strategies.

Despite the importance of knowing the method and cost of ejection in understanding the persistence of brood parasitism, anecdotal records of witnessed ejections of real Brownheaded Cowbird (Molothrus ater) eggs exist for only eight of ∼30 ejecter species. The probability of a host damaging its own egg while ejecting a parasite's egg is thought to be lower for hosts that grasp-eject, but grasp-ejection is an option only for hosts with appropriate bills. For hosts incapable of grasp-ejection, the cost of puncture-ejection may render acceptance adaptive. We video-recorded 12 ejections of real cowbird eggs by American Robins (Turdus migratorius) and 17 by Gray Catbirds (Dumetella carolinensis). With no damage to their own eggs, robins graspejected all cowbird eggs, whereas catbirds grasp-ejected 14 eggs and puncture-ejected three eggs. Our study revealed that a few species use a mixture of ejection methods and even large species may puncture-eject with little cost.

A previous phylogeny of New World orioles (Icterus) suggested a possible example of island-to-mainland colonization. Using two mitochondrial genes (cytochrome b and ND2), that study showed that 43 of the recognized species/ subspecies are divided into three clades (A, B, C). Because of a lack of fresh tissue, however, two key taxa—the South American Orange-crowned Oriole (I. auricapillus) and the Caribbean Hispaniola Oriole (I. dominicensis dominicensis)—were missing from that analysis. To complete the phylogeny, we sequenced both genes for these taxa and reconstructed a well-supported phylogeny via parsimony and maximum-likelihood analyses. The addition of I. d. dominicensis to the phylogeny confirms that the Greater Antillean Oriole (I. dominicensis) is polyphyletic, and taxonomic revision of this species complex is warranted. Also, the placement of I. auricapillus and I. d. dominicensis within clade A has important implications for biogeography. The revised phylogeny implies that clade A orioles colonized mainland South America from Caribbean islands. Orioles thus provide a striking example of reverse colonization that contradicts the traditional assumption in island biogeography of mainland-to-island colonization.