Avian Plumage Research Articles

Urbanization alters the geographic patterns of passerine plumage color in China

Urbanization has altered natural landscapes and serves as an environmental filter that selects species with specific traits. Coloration is an important trait associated with biotic interactions and thermoregulation, enabling species’ survival and reproductive success. However, few studies have focused on how species coloration changes in response to urbanization. Here, we used 547 passerine bird species from 42 cities and their corresponding non-urban communities in China to test whether urban species are darker and if they have duller plumage colors than their non-urban counterparts. Furthermore, we examined whether and how urbanization influences avian plumage color homogenization and the extent to which urbanization has altered the strength of the color–latitude geographic pattern in passerine birds across China. We found a 3.2% loss in the coloration space of birds after urbanization, although there were no significant differences in the individual dimensions of colorfulness and lightness between urban and non-urban birds. Avian communities in cities exhibited more plumage color homogenization than those in non-urban communities. There were significant latitudinal gradients in plumage colorfulness and lightness in non-urban communities, but these correlations were weaker in urban communities. Non-urban communities that were more colorful and lighter tended to be duller and darker in urban environments, and vice versa. Our results provide national-scale evidence that urbanization has led to reduced color diversity, increased color-based community similarity, and altered geographic patterns of avian plumage color gradients in China. These findings provide new insights into how rapid human-induced environmental changes have affected animal coloration during the Anthropocene.

Stabilizing selection on a plumage-based foraging adaptation: hooded warblers with average-sized white tail spots live longer.

Avian flush-pursuit insectivores typically use contrasting white plumage patches in their tails or wings to startle potential prey. Although experimental evidence indicates that the extent of white has been fine-tuned by natural selection to optimize foraging performance, the hypothesis that within-population plumage variation directly influences survival or lifetime reproduction and is subject to stabilizing selection has not been tested. Here, I provide such a test using data collected as part of a 14-year study of a colour-ringed breeding population of the hooded warbler (Setophaga citrina), a migratory flush-pursuit insectivore that shows inter-individual variation in the extent of white in the tail that is highly repeatable across moults and probably heritable. As expected under stabilizing selection, warblers with average-sized white tail patches achieved significantly higher apparent long-term survival than individuals with either a lesser or greater extent of white in the tail. Evidence of stabilizing selection was especially strong in males, an observation that is probably related to pronounced sexual habitat segregation on the wintering range. My results provide infrequently observed evidence of stabilizing selection operating in a natural population, and also illustrate how stabilizing selection can act on avian plumage traits outside the context of sexual and social signalling.

Avian nuptial plumage coloration changes differently when exposed to urban and rural areas

Avian plumage coloration could be altered by external factors like dust accumulation, but the effect of environmental conditions on such post-moult colour changes are poorly studied. Here, we investigated how exposure to the atmosphere in habitats of differing anthropogenic pressures modifies UV/blue structural plumage coloration — a sexually selected trait in eastern bluebirds Sialia sialis. We collected feather samples from live birds and distributed them in three types of habitats: (i) urban roads with low traffic, (ii) urban roads with high traffic, and (iii) rural roads with low traffic. After 4 weeks, the brightness of feathers decreased in all types of habitats-resulting in less-ornamented coloration. Changes in UV and blue chroma, however, varied with habitat type; chroma decreased in urban areas (becoming less ornamented), but increased in rural locations (becoming more ornamented). According to physiological models of avian colour vision, however, these changes in coloration tended to be below perceptual thresholds. Our results underscore the importance of how human activity can influence plumage colour of individual birds during the period between moult cycles which could have an impact on avian visual signalling. The study opens venues for further studies focusing on how the optical properties of specific airborne particles can influence coloration of wild-living animals.Significance statementPlumage coloration plays an important role in avian visual communication. In addition to moult-based change, coloration may change between moult cycles due to exposure to external factors like, for example, dust accumulation. Ecological factors modifying a passive plumage change, however, remains poorly studied. We collected samples of structurally coloured feather from a species wherein plumage colour is sexually selected and exposed them to outdoor conditions. We demonstrate that UV/blue chroma of coloration changes differently in urban and rural habitats. It increased in rural and decreased in urban areas. On the other hand, brightness decreased in both habitat types. Using physiological models of avian colour vision, however, we found that these colour changes were likely not perceptible to birds. Our study provides the first evidence that changes in coloration of fully grown feathers may be habitat dependent.

Deer management influences perception of avian plumage in temperate deciduous forests

Many animals use visual signals to communicate; birds use colorful plumage to attract mates and repel intruders. Visual signal conspicuousness is influenced by the lighting environment, which can be altered by human-induced changes. For example, deer-management efforts can affect vegetation structure and light availability. Whether these changes alter animal communication is still unknown. We investigated the effect of deer management on forest light and the contrast of understory birds against the forest background. We modeled visual perception using: (1) an ultraviolet-sensitive (UVS) avian model and plumage parameters representative of red, yellow, and blue birds (2) species-specific turkey visual and plumage parameters, and (3) individual-specific brown-headed cowbird visual and plumage parameters. Deer management led to greater light irradiance and lowered forest background reflectance. Management increased chromatic contrasts in the UVS model, primarily in deciduous forests and low understory, and across all habitat types in turkey and cowbird models. Deer management did not affect achromatic contrasts in the UVS model, but was associated with lower contrast in mixed forests for turkeys and across habitats for cowbirds. Together, this suggests that management of deer browsing is likely to impact visual signaling for a wide range of avian species. However, we also suspect that species- and individual-specific parameters increased the resolution of models, warranting consideration in future studies. Further work should determine if differences in visual perception translate to biologically relevant consequences. Our results suggest that, at least for some species, deer browsing and anthropogenic change may impose an evolutionary driver on visual communication.

Host-Parasite Relationships of Quill Mites (Syringophilidae) and Parrots (Psittaciformes)

The family Syringophilidae (Acari: Prostigmata) includes obligatory ectoparasites, which occupy feather quills from various parts of avian plumage, where they feed and reproduce. Our study was concerned with the global fauna of syringophilid mites associated with Psittaciformes, as well as host-parasite specificity and evolution. We assumed that the system composed of quill mites and parrots represents a model group that can be used in a broader study of the relationships between parasites and hosts. In total, we examined 1524 host individuals of parrots belonging to 195 species, 73 genera, and 4 families (which constitute ca. 50% of global parrot fauna) from all zoogeographical regions where Psittaciformes occur. Among them, 89 individuals representing 81 species have been infested by quill mites belonging to 45 species and 8 genera. The prevalence of host infestations by syringophilid mites varied from 2.8% to 100% (95% confidence interval (CI Sterne method) = 0.1–100). We applied a bipartite analysis to determine the parasite-host interaction, network indices, and host specificity at the species and whole network levels. The Syringophilidae-Psittaciformes network was composed of 24 mite species and 47 host species. The bipartite network was characterized by a high network level specialization H2′ = 0.98, connectance C = 0.89, and high modularity Q = 0.90, with 23 modules, but low nestedness N = 0.0333. Moreover, we reconstructed the phylogeny of the quill mites on the generic level, and this analysis shows two distinct clades: Psittaciphilus (Peristerophila + Terratosyringophilus) (among Syringophilinae subfamily) and Lawrencipicobia (Pipicobia + Rafapicobia) (among Picobiinae). Finally, the distributions and host-parasite relationships in the system composed of syringophilid mites and parrots are discussed.

A high-quality assembly reveals genomic characteristics, phylogenetic status, and causal genes for leucism plumage of Indian peafowl.

BackgroundThe dazzling phenotypic characteristics of male Indian peafowl (Pavo cristatus) are attractive both to the female of the species and to humans. However, little is known about the evolution of the phenotype and phylogeny of these birds at the whole-genome level. So far, there are no reports regarding the genetic mechanism of the formation of leucism plumage in this variant of Indian peafowl.ResultsA draft genome of Indian peafowl was assembled, with a genome size of 1.05 Gb (the sequencing depth is 362×), and contig and scaffold N50 were up to 6.2 and 11.4 Mb, respectively. Compared with other birds, Indian peafowl showed changes in terms of metabolism, immunity, and skeletal and feather development, which provided a novel insight into the phenotypic evolution of peafowl, such as the large body size and feather morphologies. Moreover, we determined that the phylogeny of Indian peafowl was more closely linked to turkey than chicken. Specifically, we first identified that PMEL was a potential causal gene leading to the formation of the leucism plumage variant in Indian peafowl.ConclusionsThis study provides an Indian peafowl genome of high quality, as well as a novel understanding of phenotypic evolution and phylogeny of Indian peafowl. These results provide a valuable reference for the study of avian genome evolution. Furthermore, the discovery of the genetic mechanism for the development of leucism plumage is both a breakthrough in the exploration of peafowl plumage and also offers clues and directions for further investigations of the avian plumage coloration and artificial breeding in peafowl.

Estimating the distribution of carotenoid coloration in skin and integumentary structures of birds and extinct dinosaurs

Carotenoids are pigments responsible for most bright yellow, red, and orange hues in birds. Their distribution has been investigated in avian plumage, but the evolution of their expression in skin and other integumentary structures has not been approached in detail. Here, we investigate the expression of carotenoid-consistent coloration across tissue types in all extant, nonpasserine species (n = 4022) and archelosaur outgroups in a phylogenetic framework. We collect dietary data for a subset of birds and investigate how dietary carotenoid intake may relate to carotenoid expression in various tissues. We find that carotenoid-consistent expression in skin or nonplumage keratin has a 50% probability of being present in the most recent common ancestor of Archosauria. Skin expression has a similar probability at the base of the avian crown clade, but plumage expression is unambiguously absent in that ancestor and shows hundreds of independent gains within nonpasserine neognaths, consistent with previous studies. Although our data do not support a strict sequence of tissue expression in nonpasserine birds, we find support that expression of carotenoid-consistent color in nonplumage integument structures might evolve in a correlated manner and feathers are rarely the only region of expression. Taxa with diets high in carotenoid content also show expression in more body regions and tissue types. Our results may inform targeted assays for carotenoids in tissues other than feathers, and expectations of these pigments in nonavian dinosaurs. In extinct groups, bare-skin regions and the rhamphotheca, especially in species with diets rich in plants, may express these pigments, which are not expected in feathers or feather homologues.

We encourage the collection of more data to better understand the visual ecology of birds: A counter-response to O'Daniels et al. (2021)

Wisenden et al. (2020) reported differential behavioral responses by male Red-winged Blackbirds (Agelaius phoeniceus) to models bearing a red-epaulet visual signal with and without reflectance in the ultraviolet (UV) portion of the spectrum. O'Daniels et al. (2021) wrote a response, claiming that some of our key terminology was incorrect and that our methodology was potentially confounded, calling into question the veracity of the results reported in our study. Herein, we explain (1) our use of the term “control” to be the treatment that lacks the test variable of interest; (2) the labels UV+and UV–refer to treatments that did, and did not, reflect in the UV; (3) that sunscreen likely did not contain methyl anthranilate, and even if it did, the amounts of sunscreen used were so small that it could not possibly explain the behavioral effects we observed over the distances between models and territorial males tested in the field; and (4) visual modeling would not enhance the interpretation or impact of our study. We do agree with O'Daniels et al. (2021) that additional field research should be done to better understand visual ecology and the evolution of avian plumage signals.

Elevational plumage divergence in the Rufous‐capped Babbler (Cyanoderma ruficeps) on a mountainous island

Environment plays an important role in the evolution of plumage coloration in birds and may also lead to sexual dichromatism if males and females face different selection pressures. Mountains exhibit varying ecological conditions along their elevation gradient that may impose divergent selection on elevationally widespread species, causing intraspecific plumage divergence. For example, UV light environments often vary between montane and lowland habitats, which could potentially cause differences in plumage UV reflection between birds occurring in the two types of habitats. However, few studies have examined the effects of elevation on plumage evolution. In this study, we quantified the plumage coloration of the Rufous‐capped Babbler Cyanoderma ruficeps from montane and lowland habitats on a mountainous island, Taiwan. We aimed to examine whether their plumage showed differences associated with changing ecological environments across the elevational gradient. The results supported that the plumage of babblers occupying montane habitats had higher UV‐reflectance and brightness than that of lowland birds, corresponding to the higher UV intensity in montane than lowland background light environments. The elevational differences were mainly found across the ventral parts of babblers that had relatively higher levels of UV reflectance compared with their dorsal parts. Alternatively, the brighter plumage, with higher UV‐reflectance in montane than lowland birds, might be mediated by physiological adaptation to other ecological factors, such as parasite pressures. The elevational differences in plumage UV‐reflectance and brightness were more dramatic in males than in females. However, we found significant sexual dichromatism in different body parts between montane and lowland babblers in which females had brighter or stronger UV‐associated coloration than males, suggesting that sexual selection has little impact on babbler plumage. Our study suggests the importance of elevational divergent selection associated with UV light or other ecological environments on avian plumage evolution.

Avian Coloration Genetics: Recent Advances and Emerging Questions.

The colorful phenotypes of birds have long provided rich source material for evolutionary biologists. Avian plumage, beaks, skin, and eggs-which exhibit a stunning range of cryptic and conspicuous forms-inspired early work on adaptive coloration. More recently, avian color has fueled discoveries on the physiological, developmental, and-increasingly-genetic mechanisms responsible for phenotypic variation. The relative ease with which avian color traits can be quantified has made birds an attractive system for uncovering links between phenotype and genotype. Accordingly, the field of avian coloration genetics is burgeoning. In this review, we highlight recent advances and emerging questions associated with the genetic underpinnings of bird color. We start by describing breakthroughs related to 2 pigment classes: carotenoids that produce red, yellow, and orange in most birds and psittacofulvins that produce similar colors in parrots. We then discuss structural colors, which are produced by the interaction of light with nanoscale materials and greatly extend the plumage palette. Structural color genetics remain understudied-but this paradigm is changing. We next explore how colors that arise from interactions among pigmentary and structural mechanisms may be controlled by genes that are co-expressed or co-regulated. We also identify opportunities to investigate genes mediating within-feather micropatterning and the coloration of bare parts and eggs. We conclude by spotlighting 2 research areas-mechanistic links between color vision and color production, and speciation-that have been invigorated by genetic insights, a trend likely to continue as new genomic approaches are applied to non-model species.

Interpreting the Image on the Konda Plaque

The research featured the authentic composition on a IX–XX century plaque found near the Konda River. The article focuses on some ambiguous details of the image. For instance, the decoration of the female figure’s clothing is made up of several zones. Its motifs include scales and dots, which are known to represent animal hair in metalwork and ceramics. In general, the image revealed a certain parallelism in the ornamentation of human clothing, animal hair, and bird plumage. The author established a clear correlation between the zoning and motifs of the female dress and the stylized plumage of ornithomorphic creatures in Oriental toreutics. Therefore, the clothes the male character is trying to take off the woman may symbolize avian plumage. The author interpreted the plot depicted on the Konda plaque as the motif of stealing the avian gown of the peri, a mythical creature of medieval Asian folklore. According to legends, the hero had to steal peri’s clothes to marry her. Thus, the image of peri, which was popular in verbal folklore, proved to be quite common in visual art as well, in particular, in early Islamic art.

Occurrence and function of melanin‐based grey coloration in Western Palaearctic songbirds (Aves: Passeriformes)

Melanin is the most common pigment in avian plumage and has various functions, including signalling individual condition, social status, aiding in camouflage and strengthening feathers. To date, most research focusing on melanin‐based colours has focused on eumelanin black and pheomelanin rusty traits. The occurrence and function of grey melanin‐based coloration, however, remains largely unstudied. Using colour plates from a bird identification guide and a comparative phylogenetic approach, we analysed the occurrence and relative patch size of grey plumage regions in 239 passerine species belonging to 36 families occurring in the Western Palaearctic. We proposed four hypotheses to explain the evolution of grey plumage: (1) protection from visually oriented predators, (2) badges of social information, (3) sexually selected ornaments, and (4) visual enhancement of badges and ornamental colour patches via high between‐colour contrast. We tested these hypotheses by analysing the occurrence and relative size of grey patches in relation to ecological and life‐history traits and the occurrence of other colours. Moreover, we surveyed the distribution of grey over avian body regions and its adjacency to other plumage colours. Grey coloration was present in 97 species from 25 families (40.5% of all species and 69.4% of all families sampled, respectively). Our results support the idea that grey plumage evolved to provide cryptic coloration and/or as a sexual signal used in female mate choice. Grey colour occurrence was associated with less concealed nest structure and open habitats, and this effect was especially pronounced in species in which males incubate. In both sexes, grey was more abundant on the head and back regions, which are the most visible body parts during incubation. The occurrence of grey was related to a greater dichromatism and was slightly higher in males than in females, which suggests that it could have evolved in response to female mate choice. No evidence suggests that grey plumage enhances ornamental colours or acts as a competitive signal. The study provides the first insight into potential functions of grey plumage in birds. Further studies at the species level are needed to test our findings.

Plumage colouration in gulls responds to their non‐breeding climatic niche

AbstractAimGlobal variation in animal colouration has inspired ecogeographical rules that suggest common patterns of recurrent adaptations to climate. However, little attention has been paid to the relative influence of the different climatic conditions encountered by species during their annual life cycle. We explored this question by testing whether breeding or non‐breeding climatic conditions most influence plumage colouration in gulls, a cosmopolitan group of birds with extensive variation in plumage darkness and seasonal migratory strategies.LocationGlobal.Time periodContemporary.Major taxa studiedAll species and subspecies of gulls (Aves, Laridae).MethodsWe used literature data and digital images to assess two characteristics of plumage colouration in all 80 species and subspecies of gulls: the darkness of the mantle and the proportion of black on wingtips. For each species and subspecies, we collected data on migration distance and environmental variables across its breeding and non‐breeding range for both breeding and non‐breeding seasons. We performed a phylogenetic comparative analysis to quantify the relative influence of climatic conditions experienced during the breeding and non‐breeding season on plumage colouration.ResultsThe climatic conditions encountered during the non‐breeding season explained interspecific variation in colouration better than the climate experienced during the breeding season. In accordance with hypotheses on the role of dark colouration in thermoregulation and feather protection, darker mantle colouration was positively correlated with insolation and negatively with air temperature. The proportion of black on wingtips was greater for long distance migrants wintering under insolated conditions than short distance migrants or residents occupying less insolated regions.Main conclusionsIn gulls, plumage colouration is predominantly shaped by selection experienced outside the breeding period, in accordance with the hypothesized photoprotective and thermoregulatory functions of avian plumage. This highlights the importance of taking into account seasonality and migration to understand global spatial patterns of avian colouration.

Does solar irradiation drive community assembly of vulture plumage microbiotas?

BackgroundStereotyped sunning behaviour in birds has been hypothesized to inhibit keratin-degrading bacteria but there is little evidence that solar irradiation affects community assembly and abundance of plumage microbiota. The monophyletic New World vultures (Cathartiformes) are renowned for scavenging vertebrate carrion, spread-wing sunning at roosts, and thermal soaring. Few avian species experience greater exposure to solar irradiation. We used 16S rRNA sequencing to investigate the plumage microbiota of wild individuals of five sympatric species of vultures in Guyana.ResultsThe exceptionally diverse plumage microbiotas (631 genera of Bacteria and Archaea) were numerically dominated by bacterial genera resistant to ultraviolet (UV) light, desiccation, and high ambient temperatures, and genera known for forming desiccation-resistant endospores (phylum Firmicutes, order Clostridiales). The extremophile genera Deinococcus (phylum Deinococcus-Thermus) and Hymenobacter (phylum, Bacteroidetes), rare in vertebrate gut microbiotas, accounted for 9.1% of 2.7 million sequences (CSS normalized and log2 transformed). Five bacterial genera known to exhibit strong keratinolytic capacities in vitro (Bacillus, Enterococcus, Pseudomonas, Staphylococcus, and Streptomyces) were less abundant (totaling 4%) in vulture plumage.ConclusionsBacterial rank-abundance profiles from melanized vulture plumage have no known analog in the integumentary systems of terrestrial vertebrates. The prominence of UV-resistant extremophiles suggests that solar irradiation may play a significant role in the assembly of vulture plumage microbiotas. Our results highlight the need for controlled in vivo experiments to test the effects of UV on microbial communities of avian plumage.

Avian Pigment Pattern Formation: Developmental Control of Macro- (Across the Body) and Micro- (Within a Feather) Level of Pigment Patterns.

Animal color patterns are of interest to many fields, such as developmental biology, evolutionary biology, ethology, mathematical biology, bio-mimetics, etc. The skin provides easy access to experimentation and analysis enabling the developmental pigment patterning process to be analyzed at the cellular and molecular level. Studies in animals with distinct pigment patterns (such as zebrafish, horse, feline, etc.) have revealed some genetic information underlying color pattern formation. Yet, how the complex pigment patterns in diverse avian species are established remains an open question. Here we summarize recent progress. Avian plumage shows color patterns occurring at different spatial levels. The two main levels are macro- (across the body) and micro- (within a feather) pigment patterns. At the cellular level, colors are mainly produced by melanocytes generating eumelanin (black) and pheomelanin (yellow, orange). These melanin-based patterns are regulated by melanocyte migration, differentiation, cell death, and/or interaction with neighboring skin cells. In addition, non-melanin chemical pigments and structural colors add more colors to the available palette in different cell types or skin regions. We discuss classic and recent tissue transplantation experiments that explore the avian pigment patterning process and some potential molecular mechanisms. We find color patterns can be controlled autonomously by melanocytes but also non-autonomously by dermal cells. Complex plumage color patterns are generated by the combination of these multi-scale patterning mechanisms. These interactions can be further modulated by environmental factors such as sex hormones, which generate striking sexual dimorphic colors in avian integuments and can also be influenced by seasons and aging.

Insulin-like growth factor 1 is related to the expression of plumage traits in a passerine species

Avian plumage colors and ornaments are excellent models to study the endocrine mechanisms linking sexually selected traits and individual parameters of quality and condition. Insulin-like growth factor 1 (IGF-1) is an evolutionarily highly conserved peptide hormone. Its regulatory role in cell proliferation and differentiation and its high sensitivity to the nutritional state of individuals suggest it as an interesting candidate, possibly providing a link between body condition and individual capacity to grow elaborated ornamental features. We investigated whether IGF-1 levels during molting correlate with the expression of multiple ornaments in a sexually dichromatic passerine species, the bearded reedling (Panurus biarmicus). We collected blood samples of males and females shortly before the molting completed and measured the size and colors of ornamental traits. Our results indicate that in males, structural plumage colors, the size of the melanin-based ornament (beard), and tail length are independent traits. IGF-1 levels are associated with the length of the tail and the expression of male structural plumage components (UV coloration), but not the melanin-based ornament. In females, plumage color and tail length were independent traits, which were not related to IGF-1 levels. To the best of our knowledge, this study provides the first evidence that IGF-1 could play a role in the development of secondary sexual characters in a bird species.Significance statementIGF-1 is an evolutionarily highly conserved peptide hormone, which recently entered the center stage of research enquiry in evolutionary biology. It is considered as one of the key factors shaping individual life histories, but little is known about its effects on sexually selected traits. We investigated whether IGF-1 levels during molting predict the elaboration of multiple ornamental plumage traits in male and female bearded reedlings (Panurus biarmicus). Our results indicate that higher IGF-1 levels had positive effects on male structural plumage colors and tail feather length. This is the first study, bringing indication for a potential role of IGF-1 in the expression of plumage ornaments in a bird species. Our findings suggest that IGF-1 might serve as an ideal candidate to study the mechanisms linking condition and the capacity to develop sexually selected ornaments.

Do Fruits Bearing the Red Carotenoid Rhodoxanthin Affect Avian Plumage Coloration in Japan?

Consumption of the berries of Morrow's Honeysuckle Lonicera morrowii has caused reddening of bird plumages in North America. We looked for examples of reddened feathers in Japanese birds, where the honeysuckle is native. We report the observation of legitimate reddened feathers in three Gray-headed Woodpeckers Picus canus, but are unsure whether the honeysuckle caused the color change in this instance. Morrow's Honeysuckle is uncommon in Japan, and birds rarely eat its berries. The availability of a wide variety of edible fruits may generally reduce the likelihood of avian plumage coloration being altered by shrubs such as the honeysuckle in Japan.

Experimental study of the effect of preen oil against feather bacteria in passerine birds.

Avian plumage harbors various pathogens such as feather-degrading bacteria, which have the potential to reduce host fitness. A growing body of evidence suggests that the secretion of the uropygial gland of birds-preen oil-acts as one of the first lines of defence against harmful bacteria. However, previous studies on the antimicrobial impact of preen oil have yielded controversial results. The impact of preen oil on bacterial densities of feathers was experimentally investigated in two passerine species: great tits Parus major and pied flycatchers Ficedula hypoleuca. More specifically, we tested whether the antibacterial effect of the preen oil secreted by the same individual differs from that of the preen oil originating from the gland of other species. In the laboratory, ventral feathers were treated with preen oil from (1) an individual's own gland, (2) from the gland of another passerine species, or (3) from the gland of a phylogenetically distant bird species. We detected a significant antibacterial effect of preen oil on bacteria that were attached to feathers, though the effect did not depend on whether the oil originated from the individual's own gland or from the gland of another bird species. However, treatment with preen oil suppressed the density of bacteria more in the pied flycatcher than in the great tit. This is the first study providing experimental evidence that preen oil represents an important antimicrobial mechanism against those plumage bacteria that are attached to feathers.

High-throughput sequencing is revealing genetic associations with avian plumage color

Abstract Avian evolution has generated an impressive array of patterns and colors in the ~10,000 bird species that exist on Earth. Recently, a number of exciting studies have utilized whole-genome sequencing to reveal new details on the genetics of avian plumage color. These findings provide compelling evidence for genes that underlie plumage variation across a wide variety of bird species (e.g., juncos, warblers, seedeaters, and estrildid finches). While much is known about large, body-wide color changes, these species exhibit discrete color differences across small plumage patches. Many genetic differences appear to be located in regulatory regions of genes rather than in protein-coding regions, suggesting gene expression is playing a large role in the control of these color patches. Taken together, these studies have the potential to broadly facilitate further research of sexual selection and evolution in these charismatic taxa.

Male Red-crested Cardinal plumage coloration is associated with parental abilities and breeding performance

Avian plumage coloration deriving from carotenoid-based pigments is among the most honest signals of individual quality. It has been argued that females may differentially allocate resources based on mate attractiveness or quality, paying the costs of investing more in a current breeding attempt. We tested predictions of the differential allocation hypothesis on the natural variation of carotenoid-based plumage using the brightly red-colored head plumage of the Red-crested Cardinal (Paroaria coronata). It is to our knowledge the first time this hypothesis is tested on the natural variation of this pigment on a wild bird. We found that the brightness of the males’ red plumage patch is positively associated with their reproductive success and the nest defence they provide. We also found that brighter males invest less in their offspring (by delivering less food to their nestlings and poorly cleaning the nest) than duller males and, by contrast, females mated with brighter males invest more in parental care. Our results are consistent with the differential allocation hypothesis: differential allocation allowed breeding pairs with brighter males to produce more offspring, suggesting that it can be considered adaptive and should be included in studies of eco-evolutionary dynamics.