In northern Venezuela, arid zones are represented by isolated areas, which are important from an ornithological perspective because of the occurrence of restricted-range birds, which depend exclusively on arid scrub for their survival. From September 2004 to August 2005, bird surveys were conducted bimonthly using distance sampling at point counts in six areas of northern Venezuela, which differ in size and geological origin. A total of 21 228 individuals representing 96 species and 26 families were recorded throughout the study areas. Bird species richness, community composition, and species abundance varied among areas. Number of species recorded per area ranged from 37 to 82. An analysis of similarity showed that areas differed in overall community composition based on species presence or absence (Global R = 0.68). The Vermilion Cardinal (Cardinalis phoeniceus) was the only restricted-range species with a high indicator value (52%) identified through an indicator species analysis. The most abundant birds in all six areas were widespread generalist species, such as the Tropical Mockingbird (Mimus gilvus) and Tropical Gnatcatcher (Polioptila plumbea), and only one of the restricted-range birds, the Buffy Hummingbird (Leucippus fallax), had high densities (range: 2.67–9.00 individuals ha⁻¹) throughout all the study areas. Densities of two restricted-range birds, the Yellow-shouldered Parrot (Amazona barbadensis) and Vermilion Cardinal varied among areas as a consequence of poaching in some areas. Species richness was not a reliable indicator of an area's conservation value because the protection of the area with highest species richness does not guarantee the effective conservation of all the restricted-range birds.

The Pacific island of Rota is part of the Mariana archipelago, and is located approximately 60 km north of the island of Guam. Two Rota endemics, the Mariana Crow (Corvus kubaryi) and the Rota Bridled White-eye (Zosterops rotensis), have declined dramatically in the last 20 years. We examined trends in abundance of eight terrestrial bird species (six native, two exotic) on Rota between 1982 and 2004, and found that seven of them declined significantly, with five species showing declines >50%. Only Micronesian Starlings (Aplonis opaca) increased in abundance. Declines occurred in species abundant in both forested and open habitats, suggesting that the declines were unlikely to be simply the result of deforestation. While the introduction of the brown tree snake (Boiga irregularis) on Guam caused the collapse of that island's avifauna, we do not believe that Rota's declines are due to the establishment of a snake population. Other, as yet unidentified, agents are likely to be responsible. We suggest that future research into the causative agent(s) of decline focus on the comparatively common declining species, rather than studying small populations of endangered species.

Ecological factors on the breeding grounds are expected to have a relatively large effect on the timing of molt in migratory birds breeding at middle latitudes (e.g., southern North America), because constraints on the time available to molt are probably weak. We investigated the timing of prebasic molt in adults of two migratory passerines, the endangered Black-capped Vireo (Vireo atricapilla) and the common White-eyed Vireo (V. griseus), on their breeding grounds in Texas. We compared the onset and rate of molt between sites differing in habitat and between years differing greatly in precipitation due to the El Niño–Southern Oscillation (ENSO). Black-capped Vireos began molting 13 days later (8 July) and completed molt 12 days faster (50 days) in low quality, clumped habitat than in more typical, contiguous shrubby habitat (62-day molt starting 25 June). Long-term estimates of onset and duration of molt based on study skins were intermediate. White-eyed Vireos in the site with clumped habitat also started molting significantly later (13 July), but did not molt significantly faster (56 days), than those in the shrubby site (63-day molt starting 2 July). Both species started molting significantly later in the wet La Niña year than in the year with dry El Niño conditions. Body condition did not differ between sites or years. Our molt duration estimates of ~55 days for Black-capped Vireos and ~60 days for White-eyed Vireos suggest weak time constraints on molt in these populations. This study highlights the sensitivity of molt dynamics to events and conditions during the preceding breeding season.

In a community of ≥3 competing species, one species may also have a positive indirect effect on another by suppressing a third, shared competitor. We examine the potential for similar interactions among Red-cockaded Woodpeckers (Picoides borealis) and two of its cavity kleptoparasites: southern flying squirrels (Glaucomys volans) and Red-bellied Woodpeckers (Melanerpes carolinus). We hypothesized that flying squirrels have a positive indirect effect on Red-cockaded Woodpeckers by suppressing Red-bellied Woodpeckers. We monitored occupancy of Red-cockaded Woodpecker cavities on 16 territories for one year, and then regularly removed flying squirrels from Red-cockaded Woodpecker cavities for one year on eight territories, each paired with a control. We predicted that flying squirrel removal would competitively release Red-bellied Woodpeckers, which in turn would preempt a positive occupancy response by Red-cockaded Woodpeckers. During the removal phase, flying squirrel occupancy decreased 53% on the removal territories relative to controls (0.46 vs. 0.96 cavities occupied per territory), while Red-bellied Woodpecker occupancy increased 46% (1.00 vs. 0.69 cavities per territory). Red-bellied Woodpecker occupancy increased 103% on the removals from July to December of the removal phase, when most Red-cockaded Woodpecker fledglings, potential helpers, and dispersers acquire cavities. Red-cockaded Woodpeckers failed to respond positively to the removals, apparently because Red-bellied Woodpeckers rapidly occupied the evacuated cavities. The results are consistent with the hypothesis that flying squirrels indirectly benefit Red-cockaded Woodpeckers by suppressing Red-bellied Woodpeckers. This indirect effect approximately counterbalanced the direct negative effect of flying squirrels on Red-cockaded Woodpeckers.

Black-backed Woodpeckers (Picoides arcticus) are burned-forest specialists that rely on beetles (Coleoptera) for food. In the Black Hills, South Dakota, standing dead forests resulting from mountain pine beetle (Dendroctonus ponderosae) outbreaks offer food resources for Black-backed Woodpeckers, in addition to providing habitat similar to burned forest. However, data on reproductive rates in these habitats are lacking. We estimated nest success and evaluated factors affecting nest survival of Black-backed Woodpeckers in beetle-killed forests in the Black Hills in 2004 and 2005. Nest success was 78% (n = 12) in 2004 and 44% (n = 31) in 2005. Fledging rates per pair were 2.0 ± 0.3 SE (n = 12) and 1.4 ± 0.3 SE (n = 28) in 2004 and 2005, respectively. Our results showed that temporal effects (e.g., age, date, and year) had the greatest influence on nest survival. Nest age was the most important predictor of daily nest survival; survival was higher in older nests. Nest survival was also lower later in the breeding season. The difference in nest success between the two years requires further study; however, nest success of Black-backed Woodpeckers in beetle-killed forests in the Black Hills was within the range of nest success within postfire habitats in this area. In the Black Hills, forests experiencing beetle outbreaks offer available habitat for Black-backed Woodpeckers.

Predation is a major cause of nest failure for songbirds, yet information is lacking on the relative importance of predator species in different landscapes. We identified nest predators of Golden-cheeked Warblers (Dendroica chrysoparia) in an urban landscape, compared cause-specific mortality rates between urban and rural landscapes, and evaluated whether monitoring nests with cameras affected nest survival. We monitored 68 nests with cameras in Austin, Texas, during 2005, 2006, and 2008 to identify causes of mortality, including predators, in an urban landscape. The period mortality and predation rates were 0.60 (95% CI: 0.42–0.73) and 0.52 (95% CI: 0.37–0.68), respectively. We identified predators at 20 nests: Texas rat snakes (Elaphe obsoleta lindheimerii) depredated eight nests (40%), Western Scrub-Jays (Aphelocoma californica) depredated six (30%), Cooper's Hawks (Accipter cooperii) depredated two (10%), fox squirrels (Sciurus niger) depredated three (15%), and fire ants (Solenopsis sp.) depredated one nest (5%). We compared mortality rates, predation rates, and predators of the 68 camera-monitored nests in Austin to 74 nests monitored with cameras in the rural landscape of Fort Hood, Texas, during 1997–2002 and 2005. The period mortality rate (0.63, 95% CI: 0.47–0.75), predation rate (0.59, 95% CI: 0.45–0.73), and predator composition at Fort Hood were similar to those in Austin. Nest abandonment, hatching success, and nestling survival were also similar in both landscapes. We compared nest survival of the 68 camera-monitored nests to 62 active nests monitored without video cameras in Austin; period nest survival was slightly higher for camera-monitored nests (0.40, 95% CI: 0.22–0.58) than for nests without cameras (0.37, 95% CI: 0.19–0.54).

Knowledge of how landscape structure influences patterns of animal space use is critical to developing sustainable landscape management practices. For breeding songbirds that defend a territory embedded within a larger home range, effects of structural change on movement may be manifested at multiple spatial scales. We used radio-telemetry to assess within-territory and home range space use as functions of the proportion of clearcut-harvested versus naturally unforested land for two species of Neotropical migrant songbirds. We tested whether these relationships varied with spatial scale by assessing landscape structure in both the local neighborhood (115 m radius around an individual's territory center) and across the landscape (1250 m radius). Territory size for riparian-associated male Northern Waterthrushes (Seiurus noveboracensis) was curvilinearly related to the proportion of harvested versus naturally unforested land and varied by greater than two orders of magnitude. Waterthrush territories were largest in the most heavily harvested landscapes. Home range space use by male Blackpoll Warblers (Dendroica striata), which are habitat generalists, was influenced by the ratio of clearcuts to natural gaps in both the neighborhood and landscape. Blackpolls may modify their behavior as a result of anthropogenic processes acting at both small and larger spatial scales, but we observed considerable interannual variability. Our results suggest that boreal forest–breeding passerines may be capable of modifying their space use behavior in response to moderate levels of structural change caused by forestry.

I investigated variation among 46 populations of the Fox Sparrow (Passerella iliaca) using five microsatellite loci, to determine whether populations assorted into the four groups (red, slate-colored, sooty, and thick-billed) previously defined on the basis of morphology and mitochondrial DNA (mtDNA). Results of neighbor-joining and principal components analyses showed that the red, sooty, and thick-billed phenotypic-mtDNA groups were mostly differentiated from each other. Some populations of the slate-colored group were intermingled with other groups. Thus, there was not complete agreement between microsatellites and the mtDNA gene tree. Some of the populations of slate-colored Fox Sparrows that aligned with other groups were geographically adjacent. A plot of principal components 1 and 2 showed populations of the slate-colored group surrounded by members of the other three groups, which mirrored their geographical arrangement. The lack of clear differentiation in microsatellites could be due to insufficient time for nuclear allele sorting or hybridization at group boundaries; it is likely that both are explanations. The four groups qualify as phylogenetic species that exhibit hybridization, whereas the number of biological species, although greater than currently recognized (one), depends on the amount of introgression deemed acceptable.

Mountain Plover (Charadrius montanus) is a species of conservation concern that has experienced significant habitat loss and population decline. This, coupled with previous observations that the species exhibits strong fidelity to breeding grounds, suggests that breeding populations may be genetically differentiated and possibly suffer from reduced genetic variation associated with relatively small population sizes. A previous genetic study comparing mitochondrial DNA sequences of plovers in Montana and Colorado found high levels of genetic variability and very little genetic differentiation among breeding locales. Because mitochondrial DNA can track only female movements and is sampled from only one locus, we used 14 nuclear microsatellite loci to further examine population structure, thereby both documenting male movements and providing a more comprehensive view of genetic structure. We found no significant differences among breeding populations. The most likely number of unique genetic clusters was one, suggesting that all sampled breeding locations comprise a single relatively homogenous gene pool. Levels of genetic diversity were similar across all four populations, with the greatest diversity in the southern plains population. We speculate that the lack of detectable genetic differentiation among populations is due to sufficient gene flow among breeding populations that might ensue if at least some pair bonds are formed when birds form mixed flocks on wintering grounds. This study corroborates and expands upon the findings of a previous mitochondrial DNA study providing a more comprehensive view of Mountain Plover population structure.

Stable-hydrogen isotope ratios (deuterium:protium; δD) in feathers enable researchers to evaluate patterns of avian movement and to estimate the source areas of migratory birds. However, variation in feather δD remains inadequately described, thus confounding inferences of avian movement and origin. We assessed variation within a feather and among feathers within and between tracts in three species of immature raptors. Within contour feathers, measurements of δD increased from a distal section to an adjacent, proximal section; the magnitude of δD increase varied with raptor species. Furthermore, contour and flight feathers differed systematically in their δD content. Two explanations for intrafeather and intraindividual variation warrant further investigation: (1) hydrogen isotope fractionation associated with feather growth rate, and (2) the incorporation of temporal variation in environmental δD into growing feathers. We consider these explanations for raptors and passerines, which seemingly differ in the incorporation of deuterium into feathers. Additionally, corresponding sections of multiple contour feathers exhibited better measurement repeatability than multiple sections within a contour feather; the variability of multiple δD measurements within a feather tract (geometric SD: ±3.5%) suggests that biological effects on the repeatability of δD measurements from concurrently grown feather material are difficult to distinguish from analytical effects. In most cases, intrafeather and intraindividual variation can be minimized by informed sample selection decisions, but both sources of variation must be considered when stable-hydrogen isotopes are used to infer the geographic origins of migrants, ascertain migratory connectivity, and facilitate avian conservation decisions.

Brood parasitism usually imposes several costs on individual hosts, one of which is the increased probability of brood reduction. We analyzed the effect of cowbird (Molothrus spp.) parasitism on the probability of brood reduction in the Brown-and-yellow Marshbird (Pseudoleistes virescens), a common host in the Argentinean Pampas. Using a nine-year database of nesting success of the Brown-and-yellow Marshbird, we compared the number of host fledglings produced in parasitized and unparasitized nests, and assessed the effect of year, parasitism (if the nest was parasitized or not), overall brood size (including cowbird and marshbird nestlings), and "hatching interval" (interval between the first- and last-hatched young) on the probability of brood reduction. Parasitized nests produced fewer Brown-and-yellow Marshbird fledglings. About 22% of nests suffered brood reduction and 68% of these nests were parasitized by cowbirds. A logistic regression model showed that hatching interval was the main factor associated with brood reduction in this species, being associated with both the number of cowbird eggs present in the nest and overall brood size. Our results reinforce the idea that cowbird egg-laying synchronization imposes additional costs on hosts, as it increases the probability of host brood reduction.

Characterizing avian diet is complex, especially for generalist insectivores, as food resources can vary over space and time, and individuals of different sexes and ages may consume different food. We examined diet of a generalist insectivore, the Southwestern Willow Flycatcher (Empidonax traillii extimus), at Roosevelt Lake in central Arizona from 2000 to 2004, determined from 344 fecal samples. We found that five prey categories accounted for 70% of the proportional abundance in flycatcher diet: Hymenoptera, Diptera, Cicadellidae, Coleoptera, and Formicidae, although the relative amounts of these and other taxa differed significantly among years. We detected no differences in diet between sexes of adults, but adults and nestlings differed, with higher proportions of Hymenoptera in adult samples and more Diptera in nestling samples. Using a subset of samples, we compared flycatcher diet in habitat patches dominated by native cottonwood (Populus fremontii) and willow (Salix gooddingii), exotic salt cedar (Tamarix ramosissima), or a mix of these tree species. We found that prey groups varied significantly among habitats in only one year, 2002, with Araneae, Lepidoptera, and Odonata significant indicators of native habitat, Cicadellidae and Hymenoptera significant indicators of exotic habitats, and Homoptera a significant indicator of mixed habitat. In 2002, a severe drought resulted in reduced prey base and near total reproductive failure, but we detected no major shift in the composition of adult diet during that year, suggesting that for generalists like the Southwestern Willow Flycatcher, overall insect abundance may be a more important driver of productivity than abundance of specific prey taxa.

Northwestern South America is a complex area that has witnessed the differentiation and expansion of a major portion of the Neotropical avifauna. The northern end of the Cordillera Central of the Colombian Andes contributes to this complexity by bringing a continuum of humid habitats from the Andean highlands to the lowland rainforests. We present new distributional information on 36 avian species of the cloud forests and páramos of this region (1300–3250 m), gained through eight years of fieldwork and general collecting. These new records reflect the mixed biogeographic affinities of the avifauna of the northern Cordillera Central, which is composed of taxa from the pluvial foothills of the Chocó (e.g., Indigo Flowerpiercer [Diglossa indigotica], Scarlet-and-white Tanager [Chrysothlypis salmoni]), Central America and Darién (e.g., Purple-throated Woodstar [Calliphlox mitchellii]), and elsewhere in the Andean mountains (e.g., Semicollared Hawk [Accipiter collaris], Yellow Manakin [Xenopipo flavicapilla]). In addition, we report the first or second definite Colombian records of the Pavonine Cuckoo (Dromococcyx pavoninus), Cinnamon Screech-Owl (Megascops petersoni), and Sharpbill (Oxyruncus cristatus). Our findings support Chapman's (1917) view of Colombia as being "at the crux of the problem of intercontinental relationships" of Neotropical birds.

It has been hypothesized that populations that are strongly connected between two periods of the year (i.e., individuals that breed in similar locations and also spend the nonbreeding season in similar locations) will be most vulnerable to population perturbations. Using stable-hydrogen isotopes in feathers and data from the North American Breeding Bird Survey, we examined this hypothesis for a vulnerable songbird, the Cerulean Warbler (Dendroica cerulea). Cerulean Warblers exhibit a parallel migration system, whereby western breeding populations are generally connected to southwestern wintering sites and eastern breeding populations are generally connected to northeastern wintering sites. As predicted, breeding populations that exhibited the strongest degree of migratory connectivity with a specific wintering region were also those populations that experienced the most severe declines over the past 40 years. Our results suggest that the strength of migratory connectivity should be an important factor when making resource-allocation decisions for the management and conservation of migratory species.

The Red-footed Booby (Sula sula) is considered one of the most polymorphic seabirds, with three adult plumage types recognized: white, white-tailed brown, and brown, as well as several degrees of intermediates. Here we show that there is no evidence of deviation from random mating according to plumage color in the largest population of Red-footed Boobies in the Galápagos Archipelago, based on a random sample of approximately 300 pairs, which agrees with previous results found in the Indian Ocean. We also found that the ratio of color morphs varies among islands within this archipelago, with the populations of Islas Genovesa and Wolf presenting a reversed ratio (90% brown, and 10% white) when compared to the majority of Red-footed Boobies populations worldwide. Furthermore, there was no indication of differential habitat association among morphs. We concluded that plumage color does not play an important role in mate choice, and as a result, nonrandom mating based on plumage color is likely not a selective mechanism maintaining the plumage polymorphism in this population.

Sequence variation of control region mitochondrial DNA, phylogenetic reconstruction, and analysis of molecular variance (AMOVA) were used to determine the degree of genetic structure of Yellow Warblers (Dendroica petechia) in the Galápagos Archipelago. When the Galápagos population was partitioned into subpopulations (by island), AMOVA indicated a nonsignificant level of genetic structure. The presence of the same haplotype on more than one island also indicated low genetic divergence among subpopulations. Using these sequences and those available in Genbank, we also determined the degree of divergence between the Galápagos Yellow Warbler population and other New World populations. Mean sequence divergence between the Galápagos population and Latin American populations was 3.7%, and between the Galápagos population and North American populations was 6.7%.

We examined the genetic mating system and social breeding structure of the Southern Lapwing (Vanellus chilensis), a shorebird that breeds in Brazil in secluded pairs or groups (3–4 adults). We never observed copulation between males or females of primary pairs with additional adults in groups; all recorded copulations were between primary pair members. Where DNA from primary males was available, we found mixed paternity in 18.8% of the broods (3 of 16), comprising 9.8% of the chicks (4 of 41). All broods containing young sired by different males occurred in groups. One chick had a DNA fingerprint with four novel bands but shared a high proportion of bands with both primary pair members of its group. One explanation is that the chick's mother copulated with a relative of her social mate. However, quasi parasitism (i.e., nest-sharing by two females) cannot be excluded. Our study demonstrates a flexible social and genetic mating system in Southern Lapwings.

We describe the genetic mating system of Cherrie's Tanager (Ramphocelus costaricensis) in southwestern Costa Rica. Our data represent the first analysis of the genetic mating system of any member of the tanager family, Thraupidae. For 59 nestlings sampled from 32 broods over two years, the social mother was the genetic mother for all but two nestlings. These two unmatched nestlings were in the only brood we observed of four young, which is double the modal brood size. We identified social fathers for 55 nestlings from 31 broods. Of these young, 49% of the nestlings in 55% of the broods resulted from extra-pair matings. Our data on Cherrie's Tanager do not support the prediction that asynchronously breeding, tropical species will have low levels of extra-pair fertilizations and highlight the need for more genetic studies of tropical species.

Multiscale models of nest site selection often ignore cross-scale correlations (correlations between predictor variables at different scales). We reexamined nest site selection of Chestnut-backed Chickadees (Poecile rufescens) at two scales within territories to isolate: (1) variation associated purely with variables measured at the patch (0.031 ha) and tree scales, and (2) variation shared by variables measured at the patch and tree scales. We used conditional (fixed-effect) logistic regression to build a patch, tree, and full model, and subtracted pure and shared components of variation from the deviance explained by the full model. Tree scale and patch scale variables accounted for 85% and 9% of the total explained variation, respectively. Only 6% of explained variation in nest site locations was due to cross-scale correlations. We suggest that multiscale habitat selection studies incorporate a diagnostic tool like variance decomposition to avoid spurious results caused by lack of independence of habitat relationships.

Subspecies are assumed to have unique evolutionary histories, but molecular data sometimes contradict subspecies designations based on morphology. A recent genetic survey of the Yellow-throated Warbler (Dendroica dominica) found that none of its three continental subspecies qualified as evolutionarily significant units. I performed a range-wide morphological assessment of the continental Yellow-throated Warbler subspecies in an effort to quantify their differences and examine if and how subspecific differences related to geography. Results indicated much overlap in the morphological characters most important in diagnosing Yellow-throated Warbler subspecies (bill length and the proportion of yellow in the lores), and discriminant function analysis failed to correctly assign most individuals, especially those collected near a subspecies border. There was a strong west-to-east clinal change in bill length and the proportion of yellow in the lores and no evidence of discrete morphological groups. I recommend eliminating the subspecies D. d. albilora and D. d. stoddardi because they cannot be reliably diagnosed by morphology or mtDNA.

Adult sex ratios of waterfowl often show male bias, usually explained by differential female mortality during breeding. However, the sex ratio among first-winter Common Eiders (Somateria mollissima) in Europe is already male biased; thus, the breeding mortality hypothesis cannot be the sole explanation for this phenomenon. To clarify when the observed male bias originally arises, we studied the sex ratio of hatched eider ducklings and the sex ratio of ducklings found dead prior to fledging in a wild and free-ranging population. The hatching sex ratio did not deviate from equal (50% females, n = 418). In contrast, the sex ratio of duckling carcasses was female biased (59%, n = 118), suggesting that survival of female ducklings is lower than that of males. Consequently, the adult-male bias found in many ducks may be established already during the early phases of life, despite an equal sex ratio at hatching.

We determined nest attendance patterns of Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) in Connecticut using temperature data-loggers. In this species, only females incubate and feed the young. Females maintained a stable thermal environment in their nests during incubation by modifying their attendance behavior in relation to ambient temperature; during cooler conditions, females made shorter, but more frequent, trips away from their nests to feed. Once eggs hatched, average nest temperature increased significantly. The data-loggers also recorded information on rare and unpredictable events, such as nest flooding, depredation, and fledging. Eggs and nestlings apparently tolerated nest inundation for periods averaging more than 90 min. Nestlings fledged from their nests soon after sunset on the flooding tide. Detailed insight into nest attendance behavior and the circumstances surrounding rare events such as flooding are especially important for this species of high conservation concern in which tidal inundation is the major cause of breeding failure.

The White-browed Spinetail (Hellmayrea gularis), of the Andean cloud forests, is the sole member of the genus Hellmayrea, and its phylogenetic relationships are still unresolved. The diversity of nest architectures in the family Furnariidae provides many phylogenetically informative characters; however, information on the nest of this enigmatic genus is lacking. Here, we describe four nests of Hellmayrea discovered in Ecuador. All nests were embedded within hanging masses of epiphytic moss, but were not pendulous, being supported from below or by stems incorporated in side walls. All nests were balls with a side entrance, externally built of green moss and internally of dry bamboo leaves. The bottom of the chamber was lined with Tillandsia seed down and, in one nest, tree-fern scales were also used. These first nests of Hellmayrea represent a type of nest architecture previously unknown in the family Furnariidae.