The amount of supplementary food humans provide to wild animals is increasing, yet the full effects of this provisioning remain unclear. For these effects to be assessed at the levels of both the population and the individual, the degree to which individuals are using this resource must be quantified. Traditional approaches rely on observations of feeding animals and analysis of gut contents and feces, but these have several limitations. Stable-isotope analysis can overcome some of these. If supplementary food items are isotopically distinct from natural ones, the relative contribution of supplementary food to the diet may be quantified accurately. We demonstrate how the isotopic signature of supplementary foods can be manipulated to increase their discrimination from natural food sources and provide an example of the utility of this approach in a supplementary feeding study. We provided supplementary food over a winter, then sampled birds during the following breeding season and analyzed their claws for their isotopic signature to estimate diet choices. The results highlight considerable variation in individuals' use of supplementary food, both within a study site and between different sites. Often the results from supplementation experiments are inconclusive. Even within the same species there can be an effect in one year or location but not in others, so a method for quantifying variation in food uptake could help in interpretation of the results. Stable-isotope analysis allows the effects of experimentally increased food supplies on ecology and behavior to be assessed accurately.

Studies of gene expression and transcriptome profiling often require the isolation of high-quality mRNA. Here, we examined how preservation method and the lag between collection and processing (postmortem interval; PMI) affect RNA quality and yield in field-collected samples. We subjected tissue samples of 11 House Sparrows (Passer domesticus) to two preservation treatments (flash freezing in liquid nitrogen versus treatment with Ambion's RNAlater prior to freezing) and eight PMI treatments (intervals ranging from 0 to 360 min). Mean RNA yields were significantly higher for flash-frozen tissues. Total RNA yield, as measured by a UV-vis spectrophotometer (Nanodrop), was not negatively associated with PMI in either preservation treatment, and we were able to extract RNA of quality (28S:18S fluorescence ratio >0.9) sufficient for most gene-expression applications from specimens that were held at ambient temperature for up to 6 hr postmortem. These results demonstrate that sufficient quantities of high-quality RNA can be extracted from avian tissues collected under typical field conditions. Although RNA remains stable for several hours postmortem, other studies have demonstrated that the transcriptional profile changes as a function of PMI. To increase the value of tissue samples for RNA studies we recommend that collectors include with a specimen detailed notes on the duration of the PMI as well as other extrinsic (e.g., time of day, temperature) and intrinsic (e.g., age of bird, sex) factors that influence levels of gene expression.

Many annual monitoring programs assume that availability—the probability that an animal will be visible, make an audible sound, or leave other evidence of its presence—is not changing systematically from year to year. Until recently, this assumption of unchanging availability seemed reasonable, but recent studies report changes in breeding phenology that are presumed to be linked to climate change. Because the rate of bird song is often correlated with stage of breeding, earlier breeding could shift timing of peak bird availability, changing the number of birds counted during annual surveys on set dates. Such changes could be erroneously interpreted as population trends. To better understand how changes in phenology might affect the probability of detecting birds, we modeled availabilities of 31 species in southern Alabama through the breeding season, documenting strong seasonal variation in availability. Then, using our availability estimates, we investigated whether changes in detection probabilities could underlie observed changes in the abundances of some species. We calculated the expected change in the number of times a species would be recorded during surveys conducted within fixed dates by assuming a 1-week shift in breeding activity. We found that summer residents were more likely to show changes in availability but that such changes in availability did not account for trends in Breeding Bird Survey (BBS) data for Alabama. Our results suggest that while summer residents' availability may be declining during BBS dates, population declines observed in BBS data for Alabama cannot be dismissed as due to shifting phenology.

We studied the effects of the edge between two forest types on the probability of occurrence of seven species of birds and found that four responded to the edge on only one side. Over 4 years, we measured the responses of forest birds to the edge between ponderosa pine forest undergoing restoration and neighboring untreated stands. Of the seven species analyzed, one occurred most frequently near the edge. Of the remaining six, none responded to the edge in the treated forest, but four responded in the untreated forest. Relatively few studies have examined abundance changes on both sides of an edge between distinct habitats that support similar bird communities, and predictive models of edge effects used for mapping animal responses to habitat change often assume that animal abundance will change on both sides of this sort of edge, declining near the edge in the habitat in which the species is most abundant and increasing near the edge in the habitat in which the species is less abundant. One-sided edge effects, such as those we have documented, may lead to markedly different predictions of the effects of habitat change on bird abundance in heterogeneous landscapes.

We estimated first-year and adult survival of Black Brant (Branta bernicla nigricans) from the Yukon—Kuskokwim Delta, Alaska, to assess (1) the role that first-year survival plays in declining recruitment and in the local breeding population's decline since the early 1980s and (2) the potential role of subsistence harvest in declining first-year survival. We used band-recovery models in program Mark to estimate band-recovery rates and annual survival from 1986 to 2007. The only models of band recoveries that received support contained annual variation and an additive effect of sex on band-recovery rates. The two best-supported models of annual survival differentiated between first-year and older Black Brant. The best-supported model (Akaike weight = 0.69) included a linear trend in first-year survival, while the second best-supported model (Akaike weight = 0.20) included an effect of mean gosling mass on first-year survival. Band-recovery rates corresponded to harvest rates of ∼1%, indicating that during the study period harvest was not demographically important. Adult survival was comparable (0.87) to that from other studies of this population, while first-year survival declined from 0.46 in 1986 to 0.24 in 2007. The trend of decline in first-year survival represented the effects of variation in conditions for goslings' growth in the breeding area combined with unknown effects on migration and in the wintering areas. Declining first-year survival is an important contributor to decline in the local breeding population of Black Brant.

Small black-and-white shearwaters of the genus Puffinus are distributed globally, and their phylogenetic relationships are complex and uncertain. In 1963 a small shearwater collected at Midway Atoll in the North Pacific Ocean was identified as a Little Shearwater (P. assimilis), but several physical features suggest closer alliance with Audubon's Shearwater (P. lherminieri) and its relatives. Biometrics indicate that the taxon this specimen represents is smaller than any other known shearwater, and phylogenetic analyses indicate it is distinct, with a pair-wise sequence divergence of at least 3.8% from related taxa. We thus propose a new species based on the specimen: Bryan's Shearwater (Puffinus bryani nom. nov.). The breeding and nonbreeding ranges of Bryan's Shearwater are unknown, but a physical resemblance to the North Atlantic boydi (of controversial taxonomic status within Puffinus) suggests an affiliation with subtropical or tropical waters. Bryan's Shearwater is apparently rare and could be threatened by extinction; therefore, additional information is needed to increase our understanding of this taxon and its conservation requirements.

Although some of the components of egg-size variation in birds have been studied, there is a lack of approaches in which phenotypic variation is both partitioned and its causes are analyzed. We partitioned and analyzed the phenotypic variation in egg size in 1588 eggs from 572 clutches of the Imperial Cormorant (Phalacrocorax atriceps) over three breeding seasons (2004–2006) at Punta León, Argentina. We estimated repeatability and phenotypic plasticity of egg size, investigating the effects of year, date of laying, body size, and body condition on egg-size variation within and between clutches. Egg size varied widely, the largest egg being >2× as heavy as the smallest. The repeatabilities of both egg size and mean egg size (0.761 and 0.894, respectively) are among the highest reported for any bird. Most variation among clutches was due to differences among individuals, being weakly related to date of laying and unrelated to year, body size, or body condition. Egg size decreased with the egg's order. This general pattern was not related to year, date of laying, body size, or condition. Proximate constraints did not explain variation either within or among clutches. There is no obvious adaptive benefit of intraclutch variation because the effect in brood reduction of intra-clutch variation in egg size was negligible. However, egg size was positively related with the survival time of the last (third) chick. Therefore, investing in a large third egg should benefit females of the Imperial Cormorant, a brood reducer, by keeping the last chick alive longer.

We report the results of a 40-year study of the western Red-shouldered Hawk (Buteo lineatus elegans) involving the banding of 2742 nestlings in southern California from 1970 to 2009 (this study) plus 127 nestlings banded in other California studies (1956–2008) and the analyses of 119 records of subsequent recovery from the Bird Banding Laboratory (1957–2009). Of the Red-shouldered Hawks recovered, 109 (91.6%) moved <100 km (short-distance dispersers), while 10 (8.4%) moved >100 km (long-distance dispersers). Three (2.5%), all long-distance dispersers, were vagrants (recovered outside the species' range of residency), and were found 374 to 843 km northeast and south of their banding locations in the Mojave, Great Basin, and Vizcaino deserts. The distribution of directions of short-distance dispersal was bipolar, closely corresponding with the northwest—southeast orientation of the species' range in southern California, while that of long-distance dispersers was mainly to the north. One of 10 long-distance dispersers, a nonvagrant, survived well into the age of breeding (103.0 months), whereas eight of the other nine perished before 14.5 months. The implications of vagrancy for conservation of this resident subspecies are that a relatively small source area can contribute genetic material over a vastly larger receiving area but rarely does so because of high mortality rates. Nonetheless, the movements of vagrants we documented provide evidence for the species' potential to populate new landscapes in response to changing environmental conditions and to maintain genetic heterogeneity within existing populations.

Measures of reproductive success have long been assumed to be reasonable surrogates of fitness. We examined reproductive success and recruitment at the individual and population levels in Swainson's Hawks breeding in northern California. At the population level, we investigated whether the number of individuals subsequently recruited could be predicted by the number of offspring produced in any given year, finding no evidence of differences in probability of recruitment by cohort or year. Instead, age of recruits was the best predictor of probability of their being recruited into the local breeding population. At the individual level, we used generalized linear models to examine the correlation between lifetime reproductive success of individual females and the number of their offspring recruited. For individuals, the number of fledglings produced was significantly correlated with both the number of those offspring and of grandchildren recruited into the breeding population. We also examined the relationship between the average annual reproduction of an individual and the number of offspring recruited, finding these significantly correlated. The relationship was not linear: individuals producing moderate numbers of fledglings, on average, yielded the highest numbers of recruits, reflecting a trade-off between adult survival and reproduction. These results provide evidence that monitoring of reproductive success of individuals or a population can give reasonable indices of future recruitment if the study is continued for a long period. But individuals with the highest average rate of reproduction may not be the most fit.

Many populations of the American Kestrel (Falco sparverius) are in decline; in northern populations it is unknown whether low recruitment and rates of return are due to mortality, poor detection, or dispersal. Ratios of stable hydrogen isotopes in feathers (δD_f) have been used widely to estimate origins of birds, in some cases providing estimates of adults dispersal between breeding seasons and post-natal dispersal of young. We attempted to use δD in feathers, grown during breeding, to identify returning and immigrant birds and to quantify dispersal. We used birds of known origin to establish the expected local δD_f but found a high degree of deuterium enrichment in these individuals relative to the local δD of rainfall (δD_P) and a significant difference between δD_f of nestlings and adults, which complicated the distinguishing of local birds from immigrants. We subsequently compared the δD of primary feathers and plasma of adults and tested for relationships among the δD of adult feathers and adult mass, body size, and reproductive effort at the time of growth to explore the cause of deuterium enrichment in adult feathers. Adults' feathers were significantly more deuterium-enriched than plasma, and their distribution did not overlap with that of nestlings' feathers. Larger males and females that fledged female nestlings of greater mass had feathers that were more deuterium-enriched, while males whose mates laid clutches of greater volume had less enriched feathers. We discuss our results with respect to the prevailing hypotheses for deuterium enrichment of raptor feathers, particularly the evaporative-cooling hypothesis.

The causes and consequences of coloniality in seabirds, and larids in particular, have received extensive study. Here, we use the Herring Gull (Larus argentatus) as a model organism to investigate the effect of nest density on chicks' growth rate and survival. On Appledore Island, Maine, Herring Gulls nest both in dense subcolonies and in more isolated situations, affording a unique opportunity for comparison of reproductive success of pairs nesting in both contexts on the same island. Chicks reared in dense subcolonies grew at a rate significantly higher than that of those reared in more isolated settings. Using mark-recapture analysis, we found that a chick's expected survival is dependent on hatch weight, hatch date, hatch order, and context (nest in dense or loose subcolony). The first chick to hatch in each nest had a significantly greater probability of surviving to fledging than the last-hatched chick. Last-hatched chicks had a significantly greater chance of survival from hatching to fledging if they were hatched and reared in the dense subcolony than in the loose subcolony. Further research is required to distinguish among the effects of parents' quality and age (and thus their ability to defend young and provide food), agonistic behavioral interactions, and proximity to nesting Great Black-backed Gulls (L. marinus, the main predator of Herring Gull chicks), on these differences. Our results suggest that pairs nesting in dense subcolonies benefit through chicks' greater growth rate and survival, possibly due to increased vigilance or greater access to food.

Cues and social information are important in the decisions many animals make to settle. In colonial seabirds, such decisions are based upon information gathered during a prospecting phase, in which for young individuals social information from conspecifics is key. Yet the specific cues that prospectors use, and why, remain debated questions. We used an experimental approach to evaluate a conspecific-attraction hypothesis, predicting that during nocturnal prospecting Ancient Murrelets (Synthliboramphus antiquus) use social information in the form of audio cues. Specifically, we used playback experiments to test whether prospectors use conspecific vocalizations to locate potential breeding sites, and we hypothesized that prospectors' activity should increase during playback of conspecific calls. Using an information-theoretic approach we found that, as predicted, playback increased Ancient Murrelet activity, supporting a conspecific-attraction hypothesis. During playback, activity increased over background levels by 271% at Langara Island and by 458% in the Aleutian Islands. In addition, Ancient Murrelet activity decreased with increasing wave height, as moon phase approached full, and with increasing distance to the nearest occupied colony. We conclude that prospectors use conspecific vocalizations to locate potential colony sites and that playback may be used in management to speed the process of recolonization of areas from which the species has been extirpated historically.

Both the geographic center and the shape of the hybrid zone between the Northern Spotted Owl (Strix occidentalis caurina) and California Spotted Owl (S. o. occidentalis) have been unknown because of a lack of samples from the transition zone between Mt. Shasta and Lassen Peak in northern California. However, the position of the boundary between these taxa, and their associated taxonomic rank, have important biogeographical, management, and political implications. We used sequences of the mtDNA control region from owls captured in that region to infer the quantitative structure of this contact zone. The proportion of Northern Spotted Owl haplotypes to total haplotypes fell below 50% approximately 24 km south of the Pit River; the 95% confidence interval for this transition extended from just south of the Pit River to just north of Lassen Peak. We estimated the standard width (20%–80%) of the hybrid zone, which appeared symmetrical, to be 94 km. We rejected the prior hypothesis that the boundary between Northern and California Spotted Owls was the Pit River; rather, the center of the zone did not appear to be closely associated with any obvious physical barrier to gene flow. This is the first described instance of a secondary contact zone between avian taxa that is clearly associated with Remington's Cascade—Sierran suture zone. This hybrid zone was too narrow to be consistent with neutral introgression; it is likely that there is a selective, behavioral, or demographic barrier to gene flow across the Pit River region.

After a bird's molt is complete, the coloration of its plumage may be altered by external factors such as soiling. We tested how exposure to sunlight affects plumage coloration derived from carotenoid pigments and feather nanostructure. We studied these changes in the Blue-tailed Bee-eater (Merops philippinus) because that species combines yellow chin feathers (colored by carotenoid pigments), green back feathers (colored by a combination of carotenoid pigments and feather nanostructure), and turquoise-blue rump feathers (colored by feather nanostructure). We measured reflectance of feather samples and then exposed them to sunlight in boxes that allowed penetration of both UV and visible wavelengths of light. After exposure to sunlight, reflectance spectrometry revealed that all three regions became less colorful. According to models of avian sight, chromatic aspects of color change were too small to be perceived in the majority of individuals. In contrast, the reduction in brightness after exposure to sunlight was likely visible to birds in most cases. Moreover, our results suggest that types of feather coloration differ in sensitivity to sunlight-induced change in color that is visible to birds. Structural coloration appears to be the most resistant to sunlight, carotenoid-based coloration appears to be the most sensitive, and colors produced by a combination of carotenoid pigments and feather microstructure are intermediate in sensitivity. Overall, our study demonstrates that sunlight modifies plumage coloration between successive molts but the strength of this effect on the Blue-tailed Bee-eater is relatively small and depends on the mechanism of color production.

Knowledge of stopovers made by migratory birds comes mostly from studies at relatively fine spatial scales. While this focus yields important information about processes at those scales, it ignores possible processes acting at broader spatial scales. We established an array of three automated radio-telemetry receiver towers housing ten antennas arranged to sample a landscape and its associated airspace at Lake Erie in southern Canada. We used digitally coded tags to monitor the behavior of multiple Swainson's and Hermit Thrushes (Catharus ustulatus and C. guttatus) simultaneously during fall 2008. The towers registered flight activity of 86% of the 69 radio-tagged individuals, whose flights occurred predominantly shortly after the end of evening civil twilight. We recorded 15 nocturnal flights that were not departure flights, indicating that during stopover passerines make nocturnal flights for purposes other than the continuation of migration. The flights we recorded were distributed throughout the night, and in eight cases they resulted in individuals moving many kilometers. These multiple instances of nocturnal landscape-scale movements represent an ecological process that is not detectable when the focus of sampling is too small. We suggest that in most studies of passerines' stopover ecology, researchers need to consider temporal and spatial scales more carefully.

Documenting how different regions across a species' breeding and nonbreeding range are linked via migratory movements is the first step in understanding how events in one region can influence events in others and is critical to identifying conservation threats throughout a migratory animal's annual cycle. We combined two studies that evaluated migratory connectivity in the Willow Flycatcher (Empidonax traillii), one using mitochondrial DNA sequences from 172 flycatchers sampled throughout their winter range, and another which examined morphological characteristics of 68 museum specimens collected in the winter range. Our results indicate that the four subspecies occupy distinct but overlapping regions of the winter range. Connectivity between specific breeding and winter grounds appears to be moderate to strong, with distributions that suggest migration patterns of both the chain and leap-frog types connecting the breeding and nonbreeding grounds. The Pacific lowlands of Costa Rica appear to be a key winter location for the endangered Southwestern Willow Flycatcher (E. t. extimus), although other countries in Central America may also be important for the subspecies.

The Strange-tailed Tyrant (Alectrurus risora) is an endangered obligate grassland bird that inhabits savannas, wet grasslands and marshes in southern Paraguay and northeastern Argentina. We evaluated the extent of social polygyny, main measures of reproduction (clutch size, hatching success, and chick survival), and factors that influence nest success in this species. We also estimated the reproductive success of females and males by measuring the number and fate of nesting attempts by banded females and the number of females per a male's territory. More than 80% of the males were polygynous. Males defended contiguous territories of 2-2.5 ha that included the territories of up to four females. Females built the nest, incubated the eggs, and brooded and fed the chicks. On average, successful nests fledged 2.3 chicks. Nest survival over the entire cycle was 0.23 and decreased with nest age and time of breeding. Most females made two or three nesting attempts per breeding season and bred in the same area for 2 or 3 consecutive years. In contrast, males rarely were seen in the same area more than 1 year, suggesting sexual differences in mortality. As a result of this, the reproductive succcess of females and males was similar. Our findings indicate that although males are highly polygynous and nest success is low, the high turnover of males in successive breeding seasons and the high probability of females' renesting within and in successive breeding seasons reduce the variance in reproductive success of both sexes.

Bird populations occupying managed transitional habitats often have low nest success because optimal habitat conditions are not maintained. In such cases, quantifying determinants of nest survival provides information for habitat maintenance or restoration. Our goal was to determine the current factors affecting nest survival in a managed but declining population of the Florida Scrub-Jay (Aphelocoma coerulescens) in Merritt Island National Wildlife Refuge. We used an information-theoretic approach and nest-survival models in program MARK to test a priori hypotheses for survival of Florida Scrub-Jay nests. Failure of Florida Scrub-Jay nests was common; only 35% of 614 were successful in producing at least one fledgling. Ninety-four percent of 399 nest failures were due to predation. Nest survival was highest in oak-dominated territories, varied by population center, and decreased with proximity to forest edges, as the season progressed, and with increasing accumulated rainfall prior to the nesting season. Shrub height, a primary focus of current efforts at habitat-quality assessment and management, was not well supported as a determinant of survival of Florida Scrub-Jay nests at Merritt Island. We suggest hypotheses to explain the lack of support for an effect of shrub height, and we conclude that mitigation of low nest survival at Merritt Island may require additional actions.

Many species of socially monogamous birds engage in extra-pair copulations, but the extent of extra-pair paternity varies considerably by species. The ecological conditions contributing to interspecific variation in rates of extra-pair paternity remain unclear. We used a combination of single-nucleotide polymorphisms and microsatellites to document extra-pair paternity in the Banded Wren (Thryothorus pleurostictus), a socially monogamous neotropical passerine that lives in a highly seasonal environment. The rate of extra-pair paternity was relatively low, with extra-pair males siring 4% of offspring in 10% of nests. This low rate is consistent with current hypotheses predicting low rates of extra-pair paternity in nonmigratory species in which survivorship of adults is high, and it is contrary to the pattern predicted by hypotheses linking synchronous breeding with high rates of extra-pair paternity. Extra-pair males sang better and were more genetically similar to females than the males they cuckolded, though our sample size for this comparison was limited. Our data will be useful for future comparative studies examining ecological correlates of extra-pair paternity. This study also demonstrates the utility of genotyping by single-nucleotide polymorphisms as a powerful alternative to microsatellites for assessing genetic mating systems.

The role of food in limiting migratory birds during the nonbreeding period is poorly understood, in part because of the complexities of quantifying food availability and diet. We tracked overwinter changes in the availability of arthropods and fruits, the primary winter foods of the Hermit Thrush (Catharus guttatus), a short-distance migrant. Fruit availability declined over the winter, and arthropod availability fluctuated with changing temperature. Concurrently, using fecal samples and stable isotopes, we tracked relative food consumption. In fecal samples fruit declined from early to mid season and δ¹³C and δ¹⁵N isotope signatures in blood became more enriched, consistent with a decline in fruit consumption and an increase in arthropod consumption. Larger-bodied birds, predominantly males, maintained territories in which the abundance of arthropods was higher, had a greater proportion of arthropods in their diet and less variation in δ¹³C (indicator of a stable diet) and fat loads over the winter. In contrast, smaller-bodied birds, primarily females, gained fat midwinter in response to unpredictable and lower-quality resources. These results are consistent with both a size-mediated form of dominance and sexual habitat segregation, such that smaller bodied birds, mainly females, may be behaviorally excluded from optimal territories. Future research should focus on the long-term consequences of food limitation in the nonbreeding season and size and sex-mediated dominance behavior on both the condition of birds within a season and on subsequent breeding success and survival.

Areas where divergent taxa come into secondary contact are important in identifying the reproductive barriers that may have evolved between them. Here we investigate whether song variation plays a role in maintaining a recently described hybrid zone between MacGillivray's (Oporornis tolmiei) and Mourning Warblers (O. Philadelphia) in northeastern British Columbia, Canada. We analyzed song recordings and genetic data from across the ranges of both species as well as where they occur in sympatry. We predicted that if song differences are an important pre-mating reproductive barrier between these taxa, song and genotype in the hybrid zone should covary. Using a discriminant function analysis, we show that the two species' songs are differentiated in allopatry but that songs converge in sympatry, with a weak and nonsignificant association between songs and diagnostic mitochondrial and nuclear genetic markers in the hybrid zone. These results suggest that song divergence is unlikely to be an important reproductive barrier between these taxa and that learning of the other species' song may be promoting continued hybridization. This result contrasts with studies of other species pairs that maintain song differences in sympatry and come into contact in this same geographic region.

Geographically isolated populations diverging in vocalizations and habitat use are prime candidates for diversification along the speciation/differentiation continuum. The Tawny-bellied Seedeater (Sporophila hypoxantha) is relatively widespread, thus potentially variable across its range. We investigated geographic variation in vocalizations, habitat use, and migratory behavior, identifying five regiolects (song variants encompassing extensive subpopulations of a species and all individuals within this large range), which correspond with different patterns of habitat use but arose independently of migratory behavior. Given the low level of genetic divergence in the capuchinos, a subset of the genus Sporophila that includes S. hypoxantha, the phylogenetic potential for learning in the genus, the fast temporal changes evident within regiolects (chronolects), the existence of environmental sound assimilation, and the singing of subsongs by young males, we conclude that geographic variation is due mostly to learning, the genetic makeup of the various populations having little effect. The occurrence of allopatric habitat-related regiolects with little (if any) morphological differentiation, suggests that this constitutes a plausible step toward the evolution of new species in the capuchinos. These results highlight the importance of habitat use and vocalizations in understanding the evolutionary differentiation and diversification of the seedeaters and suggest that their explosive radiation has been strongly influenced by the interplay of habitat choice, migratory behavior, and vocal differentiation.

The capuchinos, a subset of the genus Sporophila, represent a radiation of seedeaters characterized by little genetic differentiation, virtually no change in bill and body shape, marked plumage differences on a common theme, and notable differentiation in vocalizations and habitat use. We describe a distinctive variant that would have been considered a species by the traditional strictly phenotypical criteria for classification of species in the genus. This variant resembles the Tawny-bellied Seedeater (S. hypoxantha) but has a tawny, not gray, nape and back. It is also identical in pattern to the Chestnut Seedeater (S. cinnamomea) but has a tawny rather than chestnut body. We tested four hypotheses to assess the status of the variant: that it represents a new species, a hybrid S. hypoxantha × S. cinnamomea, a color morph of S. cinnamomea, or a color morph of S. hypoxantha. The variant is identical to S. hypoxantha in vocalizations and habitat use, varying geographically in parallel. Both forms breed syntopically, and the tawny variant is recorded only within the range of S. hypoxantha, with many records from areas where S. hypoxantha is the only breeding representative of the ruficollis group. We consider the tawny variant to be a color morph of S. hypoxantha. Two nontrivial evolutionary paths can constitute precursors to speciation in the capuchinos: (1) differentiation in vocalizations and habitat use arises with little plumage change in more or less geographically isolated populations, and (2) differentiation in plumage proceeds without change in vocalizations and habitat use within some populations.

The mouth coloration of passerine nestlings is hypothesized to attract parental care by increasing the visual conspicuousness of begging chicks and/or by signaling the reproductive value of nestlings. Specifically, carotenoids are often hypothesized to mediate the latter relationship. In House Sparrow (Passer domesticus) nestlings, we confirmed both the presence of carotenoids in rictal flanges and a positive relationship between carotenoid concentration and the intensity of yellow coloration. This carotenoid-based coloration was positively associated with nestling mass and with plasma carotenoid concentration. Red gape coloration also revealed titers of circulating carotenoids. Carotenoids reduced the overall brightness and the UV reflectance of flanges, an effect that may limit the detectability of carotenoid-rich mouth colors and the ability of brightness and UV coloration to function in communication. For example, flange brightness, likely the primary determinant of conspicuousness, was positively related to nestling mass and levels of circulating carotenoids but only when the reflectance effect of carotenoids was removed statistically. We found no evidence that UV coloration positively reflected nestling condition. Most aspects of mouth coloration were influenced by Julian date and differed among broods, suggesting that colors can capture information about temporal and nontemporal features of the environment experienced by nestlings and, furthermore, could have a genetic component.