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Woodstars are a clade of small hummingbirds with poorly known life history. One reason why they are insufficiently characterized is they tend to be little represented in museum collections. The Cornell Lab of Ornithology's Macaulay Library, an online database of user-uploaded photographs, is a complementary source of phenological information. Here, stimulated by our own field observations, we analyzed up to 200 photos per species from the Macaulay Library to investigate whether adult male Slender-tailed Woodstar (Chaetocercus [Microstilbon] burmeisteri), Amethyst Woodstar (Calliphlox amethystina), Chilean Woodstar (Eulidia yarrellii), Peruvian Sheartail (Thaumastura cora), and Purple-collared Woodstar (Thaumastura [Myrtis] fanny) molt into a drab-throated, nonbreeding plumage distinct from the better known iridescent-throated breeding plumage. We investigated these 5 species because adult males have elongated, dimorphic tails, meaning that we could distinguish adult males from immature males by their tail morphology alone. The photos show that, post-breeding, entire populations of Slender-tailed Woodstar and Peruvian Sheartail males replace their iridescent throat feathers with non-iridescent feathers, then molt back into their breeding plumage a few months later. The holotype of Microstilbon insperatusTodd 1913, type species of the genus Microstilbon, is an adult male of Slender-tailed Woodstar in the nonbreeding plumage that we describe here. Our data also suggest that male Amethyst, Chilean, and Purple-collared woodstars have a second distinct nonbreeding plumage. In these 3 species, photos showing the apparent drab-throated male plumage were rare, suggesting these species might have complex breeding phenology with some individuals molting into the nonbreeding plumage at the same time that others were breeding in iridescent-throated plumage. The rapidly growing number of photographs available in the Macaulay Library makes this resource valuable for documenting phenology, including for rare species such as woodstars. Las estrellitas son un clado de pequeños colibríes con historias de vida poco conocidas. Una de las razones por las que no están adecuadamente caracterizadas es que tienden a estar poco representadas en colecciones de museo. La Macaulay Library del Laboratorio de Ornitología de Cornell, una base de datos en línea de fotografías cargadas por usuarios, es una fuente complementaria de información fenológica. Aquí, estimulados por nuestras propias observaciones de campo, analizamos hasta 200 fotografías por especie de la Macaulay Library para investigar si los machos adultos de picaflor enano (Chaetocercus [Microstilbon] burmeisteri), picaflor amatista (Calliphlox amethystina), picaflor de Arica (Eulidia yarrellii), picaflor de cora (Thaumastura cora) y la estrellita de collar púrpura (Thaumastura [Myrtis] fanny) mudan a un plumaje no-reproductivo de garganta desvaída, distinto del más conocido plumaje reproductivo de garganta iridiscente. Investigamos estas 5 especies porque los machos adultos tienen colas elongadas y dimórficas, por lo cuál podemos distinguir a los machos adultos de los machos inmaduros por la morfología de su cola. Las fotografías muestran que, después de la reproducción, poblaciones enteras de machos de C. burmeisteri y T. cora reemplazan las plumas iridiscentes de su garganta con plumas no iridiscentes y luego mudan nuevamente a su plumaje nupcial unos meses después. El holotipo de Microstilbon insperatusTodd 1913, especie tipo del género Microstilbon, es un macho adulto de C. burmeisteri en el plumaje no-reproductivo que aquí describimos. Nuestros datos también sugieren que los machos de C. amethystina, E. yarrellii y T. fanny también tienen este segundo plumaje no-reproductivo distintivo. En estas 3 especies, las fotografías mostrando el aparente plumaje masculino de garganta desvaída fueron escasas, lo que sugiere que estas especies podrían tener una fenología reproductiva compleja, con algunos individuos mudando al plumaje no-reproductivo al mismo tiempo que otros se reproducen en plumaje de garganta iridiscente. El número cada vez mayor de fotografías disponibles en la Macaulay Library hace que este recurso sea valioso para documentar la fenología, incluso para especies raras como las estrellitas. Palabras clave: ciencia ciudadana, plumaje alterno, plumaje eclipse, Macaulay Library.

Males and females can be under different evolutionary pressures if sexual and natural selection is differentially operating in each sex. As a result, many species have evolved sexual dichromatism, or differences in coloration between sexes. Although sexual dichromatism is often used as an index of the magnitude of sexual selection, sexual dichromatism is a composite trait. Here, we examine the evolution of sexual dichromatism in one of the largest and most ecologically diverse families of birds, the tanagers, using the avian visual perspective and a species-level phylogeny. Our results demonstrate that the evolutionary decreases of sexual dichromatism are more often associated with larger and more frequent changes in male plumage coloration, and evolutionary increases are not more often associated with larger changes in either sex. Furthermore, we show that the crown and ventral plumage regions are correlated with sexual dichromatism in males, and that only male plumage complexity is positively correlated with sexual dichromatism. Finally, we demonstrate that light environment is important in shaping both plumage brilliance and complexity. By conducting a multilevel analysis of plumage evolution in males and females, we show that sexual dichromatism evolves via a mosaic of sexual and natural selection in both sexes.

A fascinating pattern in nature is the uneven distribution of biodiversity among clades, some with low species richness and phenotypic variation in contrast to others with remarkable species richness and phenotypic diversity. In animals, communication signals are crucial for intra-and interspecific interactions and are likely an important factor in speciation. However, evidence for the association between the evolution of such signals and speciation is mixed. In hummingbirds, plumage coloration is an important communication signal, particularly for mate selection. Here, using reflectance data for 237 hummingbird species (~66 % of total diversity), we demonstrate that color evolution rates are associated with speciation rates, and that differences among feather patches are consistent with an interplay between natural and sexual selection. We found that female color evolution rates of multiple plumage elements, including the gorget, were similar to those of males. Although male color evolution in this patch was associated with speciation, female gorget color evolution was not. In other patches, the relationship between speciation and color evolution rates was pervasive between sexes. We anticipate that future studies on animal communication will likely find that evolution of signaling traits of both sexes has played a vital role in generating signal and species diversity.

Animal pigmentation has evolved because of several adaptive functions. In the case of pigmentation produced by melanins, the most common pigments in animals, the main function is protection against UV radiation. However, pigmentation also affects animal surface's ability to absorb solar radiation and gain heat, which may represent a thermal constraint for endotherms due to their relatively high and constant body temperatures. As darker colours absorb more radiation than lighter colours, dark‐pigmented endotherm animals may exhibit limited performance under high ambient temperatures and thus be constrained at occupying hot environments. While the influence of pigmentation on the determination of the thermal niches of ectotherms, particularly reptiles, has been the focus of several studies, this remains an unexplored issue for endotherm animals. Here, we made a detailed quantification of the expression of pigmentation phenotypes produced by melanins in 96 species of birds inhabiting the Spanish sector of the Iberian Peninsula and estimated their climate niche position by calculating the effects of ambient temperature, insolation and precipitation on bird occurrence at a fine 10 × 10 km spatial scale. After controlling for the body size and the nocturnal condition of species, and for phylogenetic and spatial effects, we found a positive association between plumage reflectance and the functional response of bird distribution to spring–summer ambient temperature and insolation but not to precipitation. Thus, bird species preferentially occupying the hotter and sunnier areas of Spain exhibit lighter plumage pigmentation. Our findings suggest that darker birds are limited from occupying environments with high temperatures, unveiling a constraint in endotherms imposed by their pigmentation phenotype. A plain language summary is available for this article. Plain Language Summary

Abstract Island organisms often evolve phenotypes divergent from their mainland counterparts, providing a useful system for studying adaptation under differential selection. In the white-winged fairywren (Malurus leucopterus), subspecies on two islands have a black nuptial plumage whereas the subspecies on the Australian mainland has a blue nuptial plumage. The black subspecies have a feather nanostructure that could in principle produce a blue structural color, suggesting a blue ancestor. An earlier study proposed independent evolution of melanism on the islands based on the history of subspecies divergence. However, the genetic basis of melanism and the origin of color differentiation in this group are still unknown. Here, we used whole-genome resequencing to investigate the genetic basis of melanism by comparing the blue and black M. leucopterus subspecies to identify highly divergent genomic regions. We identified a well-known pigmentation gene ASIP and four candidate genes that may contribute to feather nanostructure development. Contrary to the prediction of convergent evolution of island melanism, we detected signatures of a selective sweep in genomic regions containing ASIP and SCUBE2 not in the black subspecies but in the blue subspecies, which possesses many derived SNPs in these regions, suggesting that the mainland subspecies has re-evolved a blue plumage from a black ancestor. This proposed re-evolution was likely driven by a preexisting female preference. Our findings provide new insight into the evolution of plumage coloration in island versus continental populations, and, importantly, we identify candidate genes that likely play roles in the development and evolution of feather structural coloration.

Although evolutionary theory predicts an association between the evolution of elaborate ornamentation and speciation, empirical evidence for links between speciation and ornament evolution has been mixed. In birds, the evolution of increasingly complex and colorful plumage may promote speciation by introducing prezygotic mating barriers. However, overall changes in color complexity, including both increases and decreases, may also promote speciation by altering the sexual signals that mediate reproductive choices. Here, we examine the relationship between complex plumage and speciation rates in the largest family of songbirds, the tanagers (Thraupidae). First, we test whether species with more complex plumage coloration are associated with higher speciation rates and find no correlation. We then test whether rates of male or female plumage color complexity evolution are correlated with speciation rates. We find that elevated rates of plumage complexity evolution are associated with higher speciation rates, regardless of sex and whether species are evolving more complex or less complex ornamentation. These results extend to wholeplumage color complexity and regions important in signaling (crown and throat) but not nonsignaling regions (back and wingtip). Our results suggest that the extent of change in plumage traits, rather than overall values of plumage complexity, may play a role in speciation.

Abstract Plumage pigmentation plays critical roles in survival and reproductive success in birds, from providing camouflage and thermoregulation to mediating elaborate mating displays. The genetic and developmental origins of diverse plumage pigmentation patterns remain incompletely understood, in part, due to limited intraspecific variation and high levels of genetic divergence between distantly related species. Domestic avian species are more tractable models for understanding the genetic architecture of plumage pigmentation, but the relevance of domestic phenotypes to plumage patterns observed in the wild is not clear. Here, we used comparative genomic approaches to examine coding variation in EDNRB2, a candidate gene associated with loss of plumage melanin in several species, in representative genomes from a diverse array of wild and domestic birds. We found widespread coding variation in EDNRB2 and in other pigmentation genes with limited pleiotropic roles in development. We also found that EDNRB2-mediated melanin loss may play a critical role in establishing bright non-melanin plumage colors. This work highlights EDNRB2 as a key candidate gene for mediating the development of both interspecific and intraspecific plumage variation and demonstrates the applicability of findings in domestic species to understanding avian plumage patterning more broadly.

Many animal signals co-occur, and these signals may coevolve due to their interactive properties. Previous work has demonstrated ecological drivers of evolutionary relationships between signals and the environment, which leads to questions about why specific signal pairs evolved among species that possess multiple signals. We asked whether the coloration of different species was optimized for presentation with its natural behavioral display. We investigated this in “bee” hummingbirds, where males exhibit angle-dependent structurally-colored plumage and a stereotyped courtship (shuttle) display, by experimentally creating mismatches between the behavior and plumage of five species and quantifying how these mismatches influenced male color appearance during a display. Specifically, we photographed the plumage from a given species as we moved its feathers through the position-and-orientation-specific courtship display path of other species and quantified the resulting color appearance during the display in order to compare the mismatched color appearance to each species’natural color appearance. We found that mismatches significantly altered display flashiness (% change in coloration during displays) compared to the natural plumagebehavior pairings, and that such departures in flashiness were predicted by differences in shuttle behaviors alone. These results illustrate a tight evolutionary relationship between shuttle displays and color flashiness in these hummingbirds. Further, we found that interspecific variation in male plumage, behavior, and natural color appearance predicted deviations between natural and mismatched flashy color appearance. Altogether, our work provides a new method for testing signal coevolution and highlights the complex evolutionary relationships between multiple signals and their interactions.