Ecological factors influencing the occurrence of 'flash marks' in wading birds

1. Although the plumage of birds is important for flight and thermoregulation, it is also employed in inter- and intraspecific communication. The role in communication of particular plumage features can be studied by experiment or, as here, by correlational analysis.
2. The study was carried out on the 210 species of wading birds, such as plovers, sandpipers, thick-knees and allies, that are placed within the traditional order Charadriiformes.
3. Species differ in the location and extent of 'flash marks', patches of white on the plumage that are typically conspicuous when the bird flies. These patches occur, in various permutations in different species, on the wing (primaries, secondaries, coverts), back, rump and tail.
4. Within a phylogenetic framework, it was asked which of several broad ecological variables (migration, habitat choice, feeding technique, propensity to flock) were correlated with the occurrence of flash marks. Only flocking correlated significantly. In particular, taxa that flock have flashier backs and coverts than their non-flocking relatives.
5. Three non-exclusive explanations for this correlation are: (i) individuals that take flight to avoid a predator may benefit from signalling their take-off to flock mates which themselves then take flight; (ii) flash marks could enhance the confusion effect within flocks, making it more difficult for a predator to single out an individual; and (iii) flash marks may facilitate co-ordinated flight within flocks.     

Colour polymorphism in birds: causes and functions

We studied polymorphism in all species of birds that are presently known to show intraspecific variation in plumage colour. At least three main mechanisms have been put forward to explain the maintenance of polymorphism: apostatic, disruptive and sexual selection. All of them make partly different predictions. Our aims were to investigate evolutionary causes and adaptive functions of colour polymorphism by taking into account a number of ecological and morphological features of polymorphic species. Overall, we found 334 species showing colour polymorphism, which is 3.5% of all bird species. The occurrence of colour polymorphism was very high in Strigiformes, Ciconiiformes, Cuculiformes and Galliformes. Phylogenetically corrected analysis using independent contrasts revealed that colour polymorphism was maximally expressed in species showing a daily activity rhythm extended to day/night, living in both open and closed habitats. All these findings support the hypothesis that colour polymorphism probably evolved under selective pressures linked to bird detectability as affected by variable light conditions during activity period. Thus, we conclude that selective agents may be prey, predators and competitors, and that colour polymorphism in birds may be maintained by disruptive selection.     

Carotenoids, colour and conservation in an endangered passerine, the hihi or stitchbird (Notiomystis cincta)

Carotenoids are essential dietary components utilized not only in pigmentation but also as immuno-stimulants and antioxidants. Reduced availability can have consequences on individual health and survival, thus making carotenoids a good indicator of environmental stress. We compared carotenoid profiles and plumage colour characteristics of an endangered passerine species in New Zealand, between its remnant island source population and two reintroduced island populations. Circulating carotenoids were predominantly lutein (mean of 82.2%) and zeaxanthin (mean of 14.8%), and these were the major carotenoids present as yellow pigments in the males' plumage. There were clear differences in total carotenoid concentrations and plumage colour among the three populations. Circulating carotenoid concentration was significantly higher in one of the reintroduced populations, and the yellow plumage of males was significantly higher in both reintroduced populations in comparison with the remnant population (reflected as a significant increase in hue). Understanding how these differences arise may be of importance to this species given the health benefits carotenoids impart and our ability to select plant species containing these compounds or artificially supplement them.     

What makes a feather shine? A nanostructural basis for glossy black colours in feathers

Colours in feathers are produced by pigments or by nanostructurally organized tissues that interact with light. One of the simplest nanostructures is a single layer of keratin overlying a linearly organized layer of melanosomes that create iridescent colours of feather barbules through thin-film interference. Recently, it has been hypothesized that glossy (i.e. high specular reflectance) black feathers may be evolutionarily intermediate between matte black and iridescent feathers, and thus have a smooth keratin layer that produces gloss, but not the layered organization of melanosomes needed for iridescence. However, the morphological bases of glossiness remain unknown. Here, we use a theoretical approach to generate predictions about morphological differences between matte and glossy feathers that we then empirically test. Thin-film models predicted that glossy spectra would result from a keratin layer 110-180 nm thick and a melanin layer greater than 115 nm thick. Transmission electron microscopy data show that nanostructure of glossy barbules falls well within that range, but that of matte barbules does not. Further, glossy barbules had a thinner and more regular keratin cortex, as well as a more continuous underlying melanin layer, than matte barbules. Thus, their quasi-ordered nanostructures are morphologically intermediate between matte black and iridescent feathers, and perceived gloss may be a form of weakly chromatic iridescence.     

黄喉鹀的羽色与雄鸟质量相关性分析

在国内首次利用光纤光谱仪对鸟类的羽色进行量化和分析.对黄喉鹀Emberiza elegans雌、雄鸟羽色的差异以及雄鸟羽色与雄鸟质量的相关性分析结果表明,黄喉鹀雌、雄鸟在人眼看来相同的黄色羽和白色羽部分,在紫外光色度上却存在显著差异,雄鸟紫外光色度高于雌鸟;雄鸟的质量与脸部黑色羽的亮度、可见光色度和色调呈显著正相关,雌...     

Sexual selection: when to expect trade-offs

Empirical evidence is mixed for interspecific trade-offs in investment among sexually selected traits. One important reason may be the way resources are allocated among species. Consider a set of species that obtains the same fitness pay-off for investment in song or plumage. Simulations where resources were normally distributed among species revealed significant trade-offs between song and plumage ( ± s.d. of r = −0.54 ± 0.06). However, simulations where resources were distributed in a negative binomial fashion usually produced positive correlations (r = 0.11 ± 0.09). Repeating simulations on three published studies that concomitantly quantified elaboration of song and plumage indicated that trade-offs are likely, although these analyses make assumptions that require further evaluation. Moreover, there are currently too few empirical distributions to make generalizations about the likelihood of interspecific trade-offs in sexually selected traits.     

Uncorrelated evolution between vocal and plumage coloration traits in the trogons: a comparative study

The costs of bird song incurred in a diversity of ways may result in trade‐offs in the production and maintenance of elaborate plumage ornaments. In this paper, we examine evolutionary trade‐offs between acoustic and visual signalling in trogon birds (Trogonidae). Using multiple regressions with phylogenetically independent contrasts, we found that interspecific variation in male plumage coloration was not significantly predicted by song traits (reduced by PCA) or altitude. Although plumage coloration is expected to decrease with increases in song elaboration, both groups of variables were not related. Given that song and plumage coloration traits are likely targets of sexual selection, we also examined their relationships with sexual plumage dimorphism. We found that male carotenoid‐derived coloration was positively related to sexual plumage dimorphism, suggesting that sexual selection on male carotenoid‐derived coloration may be stronger than on melanin‐ or structurally based coloration, or than on acoustic traits. Comparative studies on other bird families accounting for the effects of phylogeny as well as environmental covariates are required to test the generality of our findings in trogons.     

Body size does not predict species richness among the metazoan phyla

We present a comparative study of the relationship between body size and described taxonomic diversity in the Metazoa. We find no pattern between body size and taxonomic diversity; neither the smallest organisms nor organisms at an intermediate body size are consistently more diverse than their closest relatives. This conclusion holds for both nonphylogenetic analysis, in which phyla are treated as independent points, and analysis of independent contrasts using several recent hypotheses of metazoan phylogeny. These results appear surprising in the context of existing models of body size distributions. However, such models are built around the prevalence of right‐skewed distributions and we find no evidence for such a distribution.     

Group-foraging is not associated with longevity in North American birds

Group-foraging is common in many animal taxa and is thought to offer protection against predators and greater foraging efficiency. Such benefits may have driven evolutionary transitions from solitary to group-foraging. Greater protection against predators and greater access to resources should reduce extrinsic sources of mortality and thus select for higher longevity according to life-history theory. I assessed the association between group-foraging and longevity in a sample of 421 North American birds. Taking into account known correlates of longevity, such as age at first reproduction and body mass, foraging group size was not correlated with maximum longevity, with and without phylogenetic correction. However, longevity increased with body mass in non-passerine birds. The results suggest that the hypothesized changes in predation risk with group size may not correlate with mortality rate in foraging birds.     

Why colour in subterranean vertebrates? Exploring the evolution of colour patterns in caecilian amphibians

The proximate functions of animal skin colour are difficult to assign as they can result from natural selection, sexual selection or neutral evolution under genetic drift. Most often colour patterns are thought to signal visual stimuli; so,their presence in subterranean taxa is perplexing. We evaluate the adaptive nature of colour patterns in nearly a third of all known species of caecilians, an order of amphibians most of which live in tropical soils and leaf litter. We found that certain colour pattern elements in caecilians can be explained based on characteristics concerning above-ground movement. Our study implies that certain caecilian colour patterns have convergently evolved under selection and we hypothesize their function most likely to be a synergy of aposematism and crypsis, related to periods when individuals move overground. In a wider context, our results suggest that very little exposure to daylight is required to evolve and maintain a varied array of colour patterns in animal skin.     

Plumage colour mutations and melanins in the feathers of the Japanese quail: a first comparison

The absorbance of melanin content from dorsal feathers was compared between wild-type Japanese quail and nine other quail plumage colours determined by single mutations in one of seven genes: extended brown ( MC1R ), yellow ( ASIP ), silver ( MITF ), lavender ( MLPH ), roux ( TYRP1 ), imperfect albinism ( SLC45A2 ) and rusty . As compared with wild-type quail, all mutations but extended brown decreased total melanins. The largest decrease was observed in quail with one of the dilution mutations at TYRP1 , MLPH or SLCA45A2 . No difference in eumelanins was found between the 10 plumage colours. Despite visible colour differences, homozygous and heterozygous mutants at MITF , or the two imperfect albino (white) and cinnamon (pale yellow) alleles at SLC45A2, could not be differentiated on the basis of melanins. In contrast, the two white phenotypes caused by mutations at MITF and SLC45A2, or the two reddish plumage colours caused by the roux and rusty non-allelic mutations had different total melanin contents. The results showed that rusty was not likely to be a dilution mutation.     

Grey plumage colouration in the duck is genetically determined by the alleles on two different, interacting loci

Based on the observation of a grey phenotype in the F₁ generation from a cross between two white plumage duck varieties, the white Kaiya and the white Liancheng , we hypothesized a possible interaction between two autosomal loci that determine grey plumage. Using the parental and F₁ individuals, seven testing combinations including five different F₁ intercrosses (F₂) and two different backcrosses (BC₁ and BC₂) were designed to test our hypothesis. It was demonstrated by chi-squared analysis that six test matings produced offspring in the expected ratios between the grey and white, with P- values ranging from 0.50 to 0.99. Another mating, where all white offspring were expected, produced 33 white individuals. These results verified that the interaction between two loci produced the grey phenotype. The C locus, which carries the recessive allele ( c ), was previously thought to be the only gene responsible for white plumage in the duck. This is the first report that an allele ( t ), carried by the white Liancheng at a different autosomal locus, also determines white plumage in ducks. Furthermore, the dominant alleles at both loci can interact with each other to produce the grey phenotype, and a new dark phenotype, observed in some F₂ individuals, can be attributed to the dosage effect of the T allele.     

The cheek plumage patch is an amplifier of dominance in great tits

Amplifiers are signals that enhance the perception of other signals or cues, but no studies to date provide empirical evidence for the role of these signals in a reproductive context. Here we use the white cheek patch of great tits as a model for studying this issue. Aggressive interactions decrease patch immaculateness, so patch size may be an amplifier of dominance, that is, more clearly reveal status. If so, in high-quality individuals patch size should correlate positively with reproductive success (here estimated by laying date, assuming that the earlier the better), whereas low-quality individuals with a large patch should only more clearly reveal their low quality and thus suffer low reproductive success, which is exactly the pattern found in males. In contrast, the cheek patch does not seem to function as an amplifier in female great tits.