Secondary sexual traits in males are thought to convey information about the quality of the male to rivals and potential mates. Semi-static signals such as sexually selected plumage are thought to convey information about how well a male fared through a critical period, such as development or molt, but it is unclear if they should relate to his current condition during the breeding season. We examined the relation between epaulet size and two measures of immune function, levels of baseline corticosterone (CORT), and body condition in adult male Red-winged Blackbirds (Agelaius phoeniceus). Epaulet size was significantly negatively related to the bacteria-killing ability (BKA) of the blood but was not related to the phytohemagglutinin swelling response. There was no significant relationship between CORT and epaulet size, but there was a significant positive relationship between CORT and BKA. In addition, BKA was significantly positively correlated with date, suggesting a possible tradeoff with breeding-related activity levels. However, body condition was not related to measures of immunity, CORT, or epaulet size. Our results indicate that male Red-winged Blackbirds with larger semi-static signals experience reduced BKA during the breeding season and that baseline levels of CORT can be positively associated with measures of immune function.

Temporal segregation is known to be an important mechanism of coexistence in many foraging guilds but has not been examined in avian scavengers. Given that carrion availability is higher in the morning than in the afternoon and that differences in wing-loading and nesting behavior may limit morning activity in some species, there is potential for temporal segregation in resource use to play an important role in the coexistence of avian scavengers. I predicted that Lappet-faced Vultures (Torgos tracheliotos), which have lower wing-loading and lower competitive abilities, would have higher abundance at carrion resources in the morning than White-backed Vultures (Gyps africanus) and Rüppell's Vultures (G. rueppellii). In addition, I predicted that differences in activity patterns among vulture species would affect foraging success. Using experimental carcasses, I examined the effect of time of day on foraging behavior. I quantified foraging success in roosting birds, measured as the proportion of individuals with a full crop. Contrary to predictions, during the dry season White-backed and Rüppell's Vultures were more abundant at carcasses in the morning and Lappet-faced Vultures were more abundant in the afternoon. In the afternoon a large proportion of the Gyps individuals appeared to be satiated and densities were lower at carcasses, perhaps creating a temporal competitive refugium in the afternoon during which Lappet-faced Vultures could feed. However, Lappet-faced Vultures have lower foraging success than White-backed and Rüppell's Vultures. These results demonstrate that temporal segregation occurs, but may not reduce competition, in this scavenging guild.

Colorful plumage traits in birds may convey multiple, redundant, or unreliable messages about an individual. Plumage may reliably convey information about disparate qualities such as age, condition, and parental ability because discrete tracts of feathers may cause individuals to incur different intrinsic or extrinsic costs. Few studies have examined the information content of plumage in a species that inhabits forest canopies, a habitat with unique light environments and selective pressures. We investigated the information content of four plumage patches (blue-green crown and rump, tail white, and black breast band) in a canopy-dwelling species, the Cerulean Warbler (Setophaga cerulea), in relation to age, condition, provisioning, and reproduction. We found that older males displayed wider breast bands, greater tail white, and crown and rump feathers with greater blue-green (435–534 nm) chroma and hue than males in their first potential breeding season. In turn, older birds were in better condition (short and long term) and were reproductively superior to younger birds. We propose that these age-related plumage differences (i.e. delayed plumage maturation) were not a consequence of a life history strategy but instead resulted from constraints during early feather molts. Within age classes, we found evidence to support the multiple messages hypothesis. Birds with greater tail white molted tails in faster, those with more exaggerated rump plumage (lower hue, greater blue-green chroma) provisioned more, and those with lower rump blue-green chroma were in better condition. Despite evidence of reliable signaling in this species, we found no strong relationships between plumage and reproductive performance, potentially because factors other than individual differences more strongly influenced fecundity.

Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. We evaluated the territorial system of the cooperative-breeding White-banded Tanager (Neothraupis fasciata) in central Brazil's savanna and present results on stability of territory site occupation, relationship between territory size and group size, and dispersal patterns. Territories (n = 27, mean per season) were monitored for 3 yr in a protected area in the cerrado of central Brazil and were defined by the minimum convex polygon method. Territory size averaged 3.7 ± 0.6 ha, and was defended by all individuals of groups of 2–8 individuals (mean = 3.4 ± 1.2). We recorded 44 dispersal events between territories, and most individuals dispersed distances equal to one territory in length. Males tended to stay in the same territory, whereas females dispersed. Our results support hypotheses that predict year-long territory defense for tropical birds. Territory size reflected group size, corroborating the hypothesis that individuals adjust the territory size to ensure the amount of resources for survival.

Phenotypic traits are important for assessing differences between populations, especially in groups with poorly resolved taxonomy. One such group, the House Wren complex, presents extensive taxonomic controversy and is thought to comprise many independent evolutionary units. Although the songs and morphological features of House Wrens (Troglodytes aedon) show extensive variation, differences between populations have not been quantified. We assessed variation in acoustic and morphometric traits within this complex and compared patterns of variation with currently recognized subspecies boundaries. First, we compared songs and morphology among eight recognized subspecies (T. a. aedon, T. a. parkmanii, T. a. cahooni, T. a. brunneicollis, T. a. nitidus, T. a. musculus, T. a. beani, and T. a. rufescens), controlling for significant effects of latitude. Second, we used variation in male song, a trait with an important role in mate choice and male–male competition, to assess divergence among subspecies. We compared variation among subspecies to variation across seven currently recognized Troglodytes species (T. hiemalis, T. pacificus, T. tanneri, T. sissonii, T. cobbi, T. rufociliatus, and T. ochraceus). Our results, based on broad sampling of songs (n = 786) and morphological traits (n = 401) from 609 locations throughout the Americas, show that most of the subspecies examined diverge in song, morphology, or both. In addition, the acoustic differences between subspecies are similar to, and in some instances greater than, the divergence between pairs of currently recognized species. Our results suggest that at least four allopatric subspecies—T. a. nitidus, T. a. musculus, T. a. beani, and T. a. rufescens—are likely different species, and we identify many other vocally and morphologically differentiated subspecies that may, upon further detailed genetic analysis, result in new species.

The fossil bird Namibiavis senutae from the early Miocene of Namibia was recently identified as an African stem-group representative of Opisthocomiformes (hoatzins). The species is known only from two wing and pectoral girdle bones, however, and the extent to which African Opisthocomiformes resembled their Neotropical relatives in skeletal morphology has remained elusive. I report a hoatzin tarsometatarsus from the middle Miocene of Maboko Island in Kenya, which, except for a peculiar autapomorphic fusion of the first metatarsal, closely matches the tarsometatarsus of the extant Opisthocomus hoazin. Although a well-founded classification on the species level is not possible, the new fossil documents the existence of essentially modern-type Opisthocomiformes in the Miocene of Africa. Being 2–2.5 Ma younger than N. senutae, the specimen further extends the temporal and spatial range of Miocene African Opisthocomiformes.

According to the “sexual selection hypothesis” (SSH), plumage conspicuousness has evolved through mate choice because it signals the quality of the bearer, and this is an honest signal because it involves a predation cost in terms of increased detectability to predators. Alternatively, according to the “unprofitable prey hypothesis” (UPH), conspicuousness is an aposematic signal indicating higher escape potential. We should expect the animals with higher predation risk (either conspicuous or dull, depending on the hypothesis) to have evolved antipredator behaviors to compensate for their higher predation risk (i.e. the “compensation hypothesis”). We tested these hypotheses by studying the vigilance behavior of wintering Eurasian Siskins (Spinus spinus) foraging on three feeders with different predation-risk and competition levels. Males were, on average, 50% more brightly colored than females. Males and females had similar wing loading, which allows us to reject male unprofitability related to higher takeoff speed. Males had shorter mean interscan durations (which improves predator detection) than females, especially at the high-predation-risk feeder (which males avoided), but the sexes did not differ in foraging-bout length, percentage of time spent scanning, and mean scan duration. In males, length of yellow tail stripe and brightness were positively correlated with percentage of time spent scanning. Therefore, our results on vigilance behavior and wing loading support the compensation hypothesis and the SSH assumption of a predation cost of conspicuousness, whereas they reject the predictions of the UPH. Compensation vigilance and other antipredator behaviors are expected to have also evolved in the conspicuous sex in other dichromatic species, and we predict that a correlation between plumage conspicuousness and vigilance should be found in future comparative studies.

Differentiation, often leading to speciation, is common among island populations of birds. However, migratory species tend to differentiate less because increased movements often preclude the extended periods of allopatry thought to be required for speciation. This interaction of isolation and migration–gene flow is a complex issue in evolutionary biology. We examined the genetics of divergence in Northern Saw-whet Owls (Aegolius acadicus), in which a migratory form (A. a. acadicus) occurs during fall migration and winter, but not at other times of the year, in the range of a sedentary, island form (A. a. brooksi) on Haida Gwaii, British Columbia. We used 2,018 base pairs of mtDNA and genomic data from 405 amplified fragment-length polymorphisms to assess the population genetics and evolutionary history of these two subspecies. Both mtDNA and nuclear genomic markers showed significant divergence between these subspecies, and mtDNA gene flow between them was very low (<1 individual generation⁻¹). These subspecies likely diverged in association with the Wisconsin glacial maximum, ∼16,000 yr BP. The refugial history of the region, life-history traits, and the maintenance of lineage integrity despite current contact suggest that this divergence occurred or is maintained through heteropatric differentiation, probably driven by a loss of migratory behavior in brooksi accompanied by local adaptations.

The Mountain Black-eye (Chlorocharis emiliae) is an endemic white-eye (Zosteropidae) of Borneo with a unique “sky island” distribution. We compared mitochondrial ND2, ND3, Cytb, and control region DNA sequences (2,194 nucleotides) to study the phylogeographic relationships of five populations of this species that span its range: Mounts Kinabalu, Trus Madi, Murud, Mulu, and Pueh. These comparisons showed that black-eyes are divided into two main clades that correspond generally to subspecific morphological groups: one in Sabah, Malaysia (Kinabalu and Trus Madi), and one in Sarawak, Malaysia (Murud, Mulu, and Pueh). The genetic and morphologic subdivision of black-eyes disputes the expected merging of populations during the Last Glacial Maximum (LGM), when montane forest presumably expanded and provided the opportunity for currently isolated populations to intermingle. Instead the genetic aging of black-eye populations indicates they diversified long before the LGM, and either did not expand sufficiently in range during the LGM to reach one another, or were reproductively isolated by the time of the LGM and thus prevented from interbreeding. Moreover, the subdivision between black-eyes in Sabah and Sarawak means that this species (and probably several other montane species) has a phylogeographic structure remarkably similar to Borneo's lowland bird populations, which are presumed to have evolved under different paleo-geographic conditions. The similar phylogeographic pattern found in both montane and lowland species requires that we rethink the causes of bird population diversification on the island of Borneo.

We studied the diversity and abundance of keratinolytic bacteria hosted by the plumage of Spectacled Thrushes (Turdus nudigenis), and their capacities to break down feathers in vitro. From 40 individuals sampled in Venezuela during the rainy and dry seasons, we isolated 18 bacterial isolates able to grow on feather meal agar, a medium selective of bacteria capable of extracting energy and nitrogen from feather keratin. Fourteen of these isolates were not previously known to grow on feather keratin. Bacillus cereus was the most prevalent, isolated from 85% of all individuals. Percentage of birds colonized by keratinolytic bacteria, prevalence of the most common bacteria, average number of bacteria species harbored per bird, and average abundance per bird of the most prevalent bacteria were not dependent on season. Capacity to degrade feathers in liquid culture varied extensively among bacterial isolates; four of them were able to noticeably damage feathers, but only B. cereus totally disintegrated them in 14 days. Degrading activity of B. cereus was as intense as that of our positive control, B. licheniformis, well known for its feather-degrading properties. The rest of the bacteria, although showing perceptible growth on feathers, did not visually damage them under our experimental conditions. Contrary to previous studies on wild birds, most feather-degrading isolates (11) in our sample were Gram-negative, likely because our culture protocol was less restrictive than that of previous studies.