Spatial Variations in the Abundance of Sporophila Seedeaters in the Southern Neotropics: Contrasting the Effects of Agricultural Development and Geographical Position

Human alterations of the habitat may interfere with the natural processes that determine spatial patterns of species abundance. We examine the geographical position hypothesis and the agricultural transformation hypothesis to explain spatial patterns in the abundance of seedeater species (Sporophila spp.) in the southern Neotropics. The geographical position hypothesis predicts decreasing abundance with increasing distance from the center to the edge of a species' geographical range, and the agricultural transformation hypothesis predicts changing abundance as a response of variations in agricultural intensity. Bird abundance and the proportion of agricultural land were estimated for 16 transects covering 500 km along a gradient of both increasing agricultural intensity and increasing distance from the center of the species' geographical ranges. We found no evidence of distance effects on seedeater abundance. Responses to agricultural intensity varied among species. Neither the geographical position nor the agricultural transformation seemed to explain the pattern of abundance of Double-collared seedeaters (S. caerulescens). Agricultural intensity accounted for 63% and 99% of the spatial variation in the abundance of Dark-throated (S. ruficollis) and Tawny-bellied (S. hypoxantha) seedeaters, supporting the agricultural transformation hypothesis. The Dark-throated seedeater seem to be more tolerant to agricultural transformation than the Tawny-bellied seedeater, as they were not recorded in areas with more than 60% and 20% of agricultural lands, respectively. Our results indicate that the Dark-throated seedeater and the Tawny-bellied seedeater will most likely face (or may be already facing) a reduction in the southern part of their geographical range due to habitat loss to agriculture.     

Morphological and plumage colour variation in the Réunion grey white‐eye (Aves: Zosterops borbonicus): assessing the role of selection

The Réunion grey white‐eye (Zosterops borbonicus), a small passerine endemic to the island of Réunion (Mascarene archipelago), constitutes an extraordinary case of phenotypic variation within a bird species, with conspicuous plumage colour differentiation at a microgeographical scale. To understand whether natural selection could explain such variability, we compared patterns of variation in morphological and plumage colour traits within and among populations. To quantify morphological variation, we used measurements obtained by Frank Gill in the 1960s from 239 individuals collected in 60 localities distributed over the entire island of Réunion. To quantify colour variation, we measured the reflectance spectra of plumage patches of 50 males from a subset of Gill's specimens belonging to the five recognized plumage colour variants and used a visual model to project these colours in an avian‐appropriate, tetrachromatic, colour space. We found that variants occupy different regions of the avian colour space and that between‐variant differences for most plumage patches could be discriminated by the birds. Differences in morphology were also detected, but these were, in general, smaller than colour differences. Overall, we found that variation in both plumage colour and morphology among variants is greater than would be expected if genetic drift alone was responsible for phenotypic divergence. As the plumage colour variants correspond to four geographical forms, our results suggest that phenotypic evolution in the Réunion grey white‐eye is at least partly explained by divergent selection in different habitats or regions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 459–473.     

Song‐based species discrimination in a rapid Neotropical radiation of grassland seedeaters

Acoustic signals among newly diverged taxa have the potential to convey species identity, information that is key to reducing hybridization. Capuchino seedeaters constitute a remarkable example of recently radiated endemic species from the grasslands of South America. They are sexually dimorphic and show striking differences in male plumage coloration and song. Contrasting with this divergence in phenotype most species show extremely low neutral genetic differentiation and lack of reciprocal monophyly, which is interpreted to be a product of recent common ancestry and hybridization. Here we use field‐based playback experiments to test for the first time if males of two species, Sporophila hypoxantha and S. palustris, discriminate between conspecific and heterospecific song. Using various measures of behavior we find that both species react more strongly to their own songs. The response to playback from another southern capuchino cannot be differentiated from that of a control song from a more distantly related Sporophila species. Additionally, we did not find evidence for reinforcement as the response of S. hypoxantha did not differ between individuals that co‐occur with S. palustris and those that do not. Our finding suggests that song, a culturally inherited trait, may help maintain reproductive isolation between species in the rapid and explosive capuchino radiation.     

Conflicting mitochondrial and nuclear paraphyly in small‐sized West African house bats (Vespertilionidae)

Vallo, P., Benda, P., Červený, J. & Koubek, P. (2012). Conflicting mitochondrial and nuclear paraphyly in small‐sized West African house bats (Vespertilionidae). —Zoologica Scripta, 42, 1–12. Hybridization between species may result in introgression of mitochondrial DNA from one species to another. Phylogenetic inference, therefore, may not recover true evolutionary relationships. In bats, there are only a few reported cases of introgressive hybridization. House bats are a genus with obscure phylogeny and taxonomy, caused mainly by morphological similarity. We undertook a detailed analysis of small‐sized West African house bats (Scotophilus), tentatively identified as S. nigritellus, to clarify relationships between two sympatric colour forms. These forms were recovered in paraphyletic position to each other in both mitochondrial and nuclear phylogenies, signifying that they are two distinct species. While the yellow‐bellied form could be assigned beyond doubt to S. nigritellus s. str., the white‐bellied form may be an as yet undescribed species. Moreover, the white‐bellied form clustered as a sister mitochondrial lineage to another species, Scotophilus leucogaster. These sister lineages differed by only 2.6–2.8% sequence divergence, which lies within the intraspecific range for this genus. Two nuclear markers, however, contradicted the sister relationship, showing them instead to be distantly related. The apparent conflict between the mitochondrial and nuclear signals suggests that past hybridization may have occurred between these morphologically distinct species.     

Ontogenetic variation in the plumage colour of female European Pied Flycatchers Ficedula hypoleuca

Although variation in the dorsal plumage colour of male European Pied Flycatchers Ficedula hypoleuca has received a great deal of attention, females of the species have been usually considered to be nearly uniformly monochromatic brown. Using reflectance spectrophotometry, we explore the age‐dependent variation of plumage colour in females. We disentangle the within‐ and between‐individual effects of this pattern and show a within‐individual darkening of the mantle colour with age, whereas differences between individuals in structural colour expression may underlie the trend for a more reflective white in the females' breast plumage with advancing age. The darkening of the dorsal plumage as females age reflects the most common pattern of age‐related variation in males in most European populations of the species.     

Geographical and seasonal variation in the intensity of sexual selection in the barn swallow Hirundo rustica: a meta‐analysis

Sexual selection arises from competition among individuals for access to mates, resulting in the evolution of conspicuous sexually selected traits, especially when inter‐sexual competition is mediated by mate choice. Different sexual selection regimes may occur among populations/subspecies within the same species. This is particularly the case when mate choice is based on multiple sexually selected traits. However, empirical evidence supporting this hypothesis at the among‐populations level is scarce. We conducted a meta‐analysis of the intensity of sexual selection on the largest database to date for a single species, the barn swallow (Hirundo rustica), relying on quantitative estimates of sexual selection. The intensity of sexual selection was expressed as the strength (effect size) of the relationships between six plumage ornaments (tail length, tail asymmetry, size of white spots on tail, ventral plumage colour, throat plumage colour and throat patch size) and several fitness proxies related to reproduction, parental care, offspring quality, arrival date from spring migration, and survival. The data were gathered for four geographically separated subspecies (H. r. rustica, H. r. erythrogaster, H. r. gutturalis, H. r. transitiva). The overall mean effect size (Z_r = 0.214; 95% confidence interval = 0.175–0.254; N = 329) was of intermediate magnitude, with intensity of sexual selection being stronger in males than in females. Effect sizes varied during the breeding cycle, being larger before egg deposition, when competition for access to mates reaches its maximum (i.e. in the promiscuous part of the breeding cycle), and decreasing thereafter. In addition, effect sizes from experiments were not significantly larger than those from correlative studies. Finally, sexual selection on different sexually dimorphic traits varied among subspecies. This last result suggests that morphological divergence among populations has partly arisen from divergent sexual selection, which may eventually lead to speciation.     

Strong reproductive isolation and narrow genomic tracts of differentiation among three woodpecker species in secondary contact

Hybrid zones allow the measurement of gene flow across the genome, producing insight into the genomic architecture of speciation. Such analysis is particularly powerful when applied to multiple pairs of hybridizing species, as patterns of genomic differentiation can then be related to age of the hybridizing species, providing a view into the build‐up of differentiation over time. We examined 33 809 single nucleotide polymorphisms (SNPs) in three hybridizing woodpecker species: Red‐breasted, Red‐naped and Yellow‐bellied sapsuckers (Sphyrapicus ruber, Sphyrapicus nuchalis and Sphyrapicus varius), two of which (ruber and nuchalis) are much more closely related than each is to the third (varius). To identify positions of SNPs on chromosomes, we developed a localization method based on comparative genomics. We found narrow clines, bimodal distributions of hybrid indices and genomic regions with decreased rates of introgression. These results suggest moderately strong reproductive isolation among species and selection against specific hybrid genotypes. We found 19 small regions of strong differentiation between species, partly shared among species pairs, but no large regions of differentiation. An association analysis revealed a single strong‐effect candidate locus associated with plumage, possibly explaining mismatch among the three species in genomic relatedness and plumage similarity. Our comparative analysis of species pairs of different age and their hybrid zones showed that moderately strong reproductive isolation can occur with little genomic differentiation, but that reproductive isolation is incomplete even with much greater genomic differentiation, implying there are long periods of time when hybridization is possible if diverging populations are in geographic contact.     

Different modes of evolution in males and females generate dichromatism in fairy‐wrens (Maluridae)

Sexual dichromatism in birds is often attributed to selection for elaboration in males. However, evolutionary changes in either sex can result in plumage differences between them, and such changes can result in either gains or losses of dimorphism. We reconstructed the evolution of plumage colors in both males and females of species in Maluridae, a family comprising the fairy‐wrens (Malurus, Clytomias, Sipodotus), emu‐wrens (Stipiturus), and grasswrens (Amytornis). Our results show that, across species, males and females differ in their patterns of color evolution. Male plumage has diverged at relatively steady rates, whereas female coloration has changed dramatically in some lineages and little in others. Accordingly, in comparisons against evolutionary models, plumage changes in males best fit a Brownian motion (BM) model, whereas plumage changes in females fit an Ornstein Uhlenbeck (OU) multioptimum model, with different adaptive peaks corresponding to distributions in either Australia or New Guinea. Levels of dichromatism were significantly associated with latitude, with greater dichromatism in more southerly taxa. Our results suggest that current patterns of plumage diversity in fairy‐wrens are a product of evolutionary changes in both sexes, driven in part by environmental differences across the distribution of the family.     

Female tawny-bellied seedeaters do not prefer more colorful males in choice experiments

Plumage coloration has long been studied as a sexually selected character. The tawny-bellied seedeater, Sporophila hypoxantha, is a sexually dichromatic species, with adult males the more colorful sex and juvenile males indistinguishable from females. We did choice experiments to evaluate female preferences for males that differ in age or plumage coloration. Females were evaluated in three experiments: (1) choice between males with similar breast brightness that differed in age, (2) choice between males of 2 years of age that differed in breast brightness, and (3) choice between males of 3 or more years of age that differed in breast brightness. We also repeated the latter experiment with estradiol-treated females. We did not find a clear female preference for brighter or older males, as females spent the same proportion of time with males of similar breast brightness that differed in age or with males of similar age that differed in breast brightness. Our results do not support the hypothesis that breast brightness is a cue used by female tawny-bellied seedeaters at the time of choosing males. We propose that, in this species, male plumage coloration might play a role in intrasexual competition.     

Feather colours of live birds and museum specimens look similar when viewed by seabirds

Bird plumage and skin colour can be assessed from museum specimens. To determine whether these accurately represent the colours of live birds when viewed by birds themselves, we analysed the spectral reflectances of live and up to 100‐year‐old museum specimens of five seabird species (White‐faced Petrel Pelagodroma marina, Common Diving Petrel Pelecanoides urinatrix, Grey‐faced Petrel Pterodroma gouldi, Little Shearwater Puffinus assimilis and Fluttering Shearwater Puffinus gavia). Live birds had brighter colours than museum specimens, but there were no significant differences in the wavelengths reflected. Modelling indicated that seabirds would be able to detect colour changes in the skin, but not the feathers, of museum specimens, but only for species with blue or pink feet (Pelecanoides urinatrix and Puffinus assimilis). For seabirds, museum specimens are adequate proxies for feather colour but not for skin colour.     

Genomic evidence for convergent evolution of a key trait underlying divergence in island birds

Reproductive isolation can be initiated by changes in one or a few key traits that prevent random mating among individuals in a population. During the early stages of speciation, when isolation is often incomplete, there will be a heterogeneous pattern of differentiation across regions of the genome between diverging populations, with loci controlling these key traits appearing the most distinct as a result of strong diversifying selection. In this study, we used Illumina‐sequenced ddRAD tags to identify genomewide patterns of differentiation in three recently diverged island populations of the Monarcha castaneiventris flycatcher of the Solomon Islands. Populations of this species have diverged in plumage colour, and these differences in plumage colour, in turn, are used in conspecific recognition and likely important in reproductive isolation. Previous candidate gene sequencing identified point mutations in MC1R and ASIP, both known pigmentation genes, to be associated with the difference in plumage colour between islands. Here, we show that background levels of genomic differentiation based on over 70,000 SNPs are extremely low between populations of distinct plumage colour, with no loci reaching the level of differentiation found in either candidate gene. Further, we found that a phylogenetic analysis based on these SNPs produced a taxonomy wherein the two melanic populations appear to have evolved convergently, rather than from a single common ancestor, in contrast to their original classification as a single subspecies. Finally, we found evidence that the pattern of low genomic differentiation is the result of both incomplete lineage sorting and gene flow between populations.     

Simple technique for distinguishing Yellow‐bellied Flycatchers from Cordilleran and Pacific‐slope flycatchers

Flycatchers of the genus Empidonax are readily misidentified in the field, in the hand, and even in museum collections. We describe a novel plumage feature that can be used to distinguish Yellow‐bellied Flycatchers (E. flaviventris) from the two species that comprise the Western Flycatcher complex, Cordilleran Flycatchers (E. occidentalis) and Pacific‐slope Flycatchers (E. difficilis). The length of the buffy fringing on the anterior edge of each secondary feather, visible on the folded wing, is significantly shorter in Yellow‐bellied Flycatchers than in Western flycatchers, with minimal overlap. A definitive identification can be made using a simple formula that includes measurements of wing chord and the length of the buffy fringing along the outer edge of the first secondary (S1). This method provides definitive in‐hand identification, and the difference in length of the buffy fringing on the secondaries is also a useful field mark for visual identification. Testing our method with 113 museum specimens that had been identified a priori based on locality, we correctly identified 112 specimens. The exception was a specimen from Illinois that had been assumed to be a Yellow‐bellied Flycatcher. However, based on our formula, it was a Western flycatcher and analysis of its mtDNA sequence confirmed this result, proving the utility of our method.     

Phylogeography of the magpie-robin species complex (Aves: Turdidae: Copsychus) reveals a Philippine species, an interesting isolating barrier and unusual dispersal patterns in the Indian Ocean and Southeast Asia

Aim The oriental magpie‐robin (Copsychus saularis) of South and Southeast Asia is a phenotypically variable species that appears to be closely related to two endemic species of the western Indian Ocean: the Madagascar magpie‐robin (Copsychus albospecularis) and the Seychelles magpie‐robin (Copsychus sechellarum). This unusual distribution led us to examine evolutionary relationships in magpie‐robins, and also the taxonomic significance of their plumage variation, via a molecular phylogenetic and population genetic analysis of C. saularis and C. albospecularis. Location Southern Asia from Nepal across Indochina to southern China, and the Indian Ocean from Madagascar to the Greater Sunda and Philippine islands. Methods We sequenced 1695 nucleotides of mitochondrial DNA comprising the complete second subunit of the nicotinamide adenine dinucleotide dehydrogenase (ND2) gene and 654 bases of the cytochrome c oxidase subunit I (COI) region in 51 individuals of eight C. saularis subspecies, 10 individuals of C. albospecularis (one subspecies) and single individuals of two other Copsychus species as outgroups. The data were analysed phylogenetically, with maximum likelihood, Bayesian, relaxed clock and parsimony methods, and geographically for patterns of genetic diversity. Results Phylogenetic analysis indicated that C. albospecularis lies within the nominal C. saularis, making C. saularis polyphyletic. Malagasy and non‐Philippine Asian populations form a monophyletic group that is sister to a clade of Philippine populations. Within non‐Philippine Asian populations, two groups are evident: black‐bellied birds in the eastern Greater Sunda islands and white‐bellied birds in the western Sundas and on mainland Asia. Main conclusions The phylogeny of magpie‐robins suggests a novel pattern of dispersal and differentiation in the Old World. Ancestral magpie‐robins appear to have spread widely among islands of the Indian Ocean in the Pliocene, probably aided by their affinity for coastal habitats. Populations subsequently became isolated in island groups, notably the Philippines, Madagascar and the Greater Sundas, leading to speciation in all three areas. Isolation in the Philippines may have been aided by competitive exclusion of C. saularis from Palawan by a congener, the white‐vented shama (Copsychus niger). In the Greater Sundas, white‐bellied populations appear to have invaded Borneo and Java recently, where they hybridize with resident black‐bellied birds.     

UV reflectance as a cue in egg discrimination in two Prinia species exploited differently by brood parasites in Taiwan

Birds are capable of seeing the ultraviolet light (UV) spectrum and as a consequence have evolved UV‐reflective structures with signalling functions. Avian eggs also reflect in the UV spectrum but the importance of UV egg matching in egg rejection decisions has been equivocal. Here we conducted egg rejection experiments in the congeneric and sympatrically breeding Yellow‐bellied Prinia Prinia flaviventris and Plain Prinia Prinia inornata in Taiwan to assess the role of UV as a cue in egg discrimination. Yellow‐bellied Prinia is a host of Oriental Cuckoo Cuculus optatus, whereas Plain Prinia is not. We coated one prinia egg in the experimental clutches with a cream containing a UV‐blocking agent, while the rest of the eggs were coated with cream only. We also experimentally parasitized prinias with non‐mimetic model eggs with reduced UV reflectance. Yellow‐bellied Prinia and Plain Prinia rejected their own UV‐blocked eggs in 18.2 and 8.3% of the experiments, respectively, and the difference was not significant. However, Yellow‐bellied Prinia rejected 100% of the non‐mimetic eggs, whereas the Plain Prinia rejected only 5%. Hence, UV reflectance alone is a cue in egg discrimination, but the importance of reflectance outside the UV spectrum in these two prinia species is much more responsive to selection as a consequence of brood parasitism.     

Lack of association between winter coat colour and genetic population structure in the Japanese hare,Lepus brachyurus (Lagomorpha: Leporidae)

Seasonal changes in fur colour in some mammalian species have long attracted the attention of biologists, especially in species showing population variation in these seasonal changes. Genetic differences among populations that show differences in seasonal changes in coat colour have been poorly studied. Because the Japanese hare (Lepus brachyurus) has two allopatric morphotypes that show remarkably different coat colours in winter, we examined the population genetic structure of the species using partial sequences of the SRY gene and six autosomal genes: three coat colour‐related genes (ASIP, TYR, and MC1R) and three putatively neutral genes (TSHB, APOB, and SPTBN1). The phylogenetic tree of SRY sequences exhibited two distinct lineages that diverged approsimately 1 Mya. Although the two lineages exhibited a clear allopatric distribution, it was not consistent with the distribution of morphotypes. In addition, six nuclear gene sequences failed to reveal genetic differences between morphotypes. Population network trees for 11 expedient populations divided the populations into four groups. Genetic structure analysis revealed an admixture of four genetic clusters in L. brachyurus, two of which showed large genetic differences. Our results suggest ancient vicariance in L. brachyurus, and we detected no genetic differences between the two morphotypes. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 761–776.     

Molecular population genetics of the melanic plumage polymorphism in Arctic skuas (Stercorarius parasiticus): evidence for divergent selection on plumage colour

The Arctic skua (Stercorarius parasiticus) is a classic example of an avian plumage polymorphism, with variation in melanin‐based ventral plumage coloration defining pale, intermediate and dark morphs in adults of both sexes. However, despite several decades of field research, there is an incomplete understanding of how the polymorphism in ventral plumage colour is maintained and the selective forces involved. Here, we investigate selection on a locus (MC1R) that is strongly associated with plumage colour variation in Arctic skuas using patterns of nucleotide variation and comparison to neutral loci (nuclear introns and mtDNA). We find that three linked nonsynonymous mutations in MC1R, including the single mutation described previously, are associated with plumage colour in the Arctic skua. The position of nonsynonymous mutations on a MC1R haplotype network implies that divergent selection drove the initial evolution of the colour morphs. Comparisons of F_STs of MC1R vs. nuclear introns among five skua populations differing in proportion of dark morphs along an approximate north–south cline reveal a signature of divergent selection on MC1R. In contrast, we find limited evidence for balancing selection on MC1R within populations, although the power is low. Our results provide strong evidence for both past and ongoing selection on MC1R, and, by implication, plumage colour in Arctic skuas. The results suggest that a fruitful avenue for future ecological studies will be analysis of selection on morphs in colonies at the extremes along the morph ratio cline.     

The anatomical basis of sexual dichromatism in non-iridescent ultraviolet-blue structural coloration of feathers

Despite extensive research on the evolution of avian dichromatism, the anatomical bases for differences between the sexes in species with structurally coloured plumage remain largely unknown. Using full‐spectrum spectrometry and transmission electron microscopy, we compared the colour and morphology of rump feathers of male and female eastern bluebirds (Sialia sialis). The ultraviolet (UV)‐blue feather colour in this species is caused by coherent scattering of light within the medullary ‘spongy layer’ of feather barbs. This spongy layer lies beneath a keratin cortex and on top of a layer of melanin granules that surround a hollow central vacuole. Irregularly shaped electron‐dense regions are present within the cortex. Male and female S. sialis differed substantially in their plumage colour and feather structure. A backwards logistic regression predicted sex with 100% accuracy using the colour variables brightness, UV‐violet (UV‐V) chroma and spectral saturation. A second backwards logistical regression predicted sex with 100% accuracy using relative cortex area and size of air spaces. Thus, S. sialis are dimorphic both in colour and in the structures causing this colour. Multiple regression analyses using data pooled from both sexes indicated that multiple features of feather barb structure contributed to colour variation in complex ways. Brightness was negatively related to the relative surface area of cortex in barb cross‐sections. Hue was positively related and UV‐V chroma was negatively related to the distance between scattering elements (i.e. keratin rods and air spaces) in the spongy layer. In contrast, hue was negatively related and UV‐V chroma was positively related to the thickness of the spongy layer. UV‐V chroma was also negatively related to the relative area of electron‐dense regions in the cortex. Spectral saturation was negatively related to the distance between scatterers and the standard error of the size of air spaces. These results suggest that the dimensions of spongy‐layer elements are critical to colour production, but that UV‐blue coloration can also be modified by the cortex and the thickness of the spongy layer. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 259–271.     

Sillem's Mountain Finch Leucosticte sillemi is a valid species of rosefinch (Carpodacus,Fringillidae)

Sillem's Mountain Finch Leucosticte sillemi was described in 1992 on the basis of an adult and an immature specimen collected in western Tibet in September 1929, but its taxonomic validity and phylogenetic position have been unclear. Based on phylogenetic analysis of mitochondrial DNA from the holotype, we show that L. sillemi is not a colour morph of Brandt's Mountain Finch Leucosticte brandti but represents a valid, previously overlooked species of rosefinch (Carpodacus) that has secondarily acquired a pale plumage convergent on that of Leucosticte. Sillem's Mountain Finch is one of the least known species of bird and represents the only known species of rosefinch in which males have no reddish plumage coloration. This species and its sister taxon, the Tibetan Rosefinch Carpodacus roborowskii, are likely to be the world's highest‐altitude sister‐species pair of birds.     

What do we really know about the signalling role of plumage colour in blue tits? A case study of impediments to progress in evolutionary biology

Evolutionary biologists seek to explain the origin and maintenance of phenotypes, and a substantial portion of this research is accomplished by thorough study of individual species. For instance, many researchers study individual species to understand evolution of ornamental traits which appear to be products of sexual selection. I explored our understanding of sexual ornaments in a well‐studied vertebrate species that may serve as a case study for research programs in evolutionary biology. I attempted to located all published papers examining plumage colour and variables related to sexual selection hypotheses in a common European songbird, the blue tit (Cyanistes caeruleus). Researchers have estimated over 1200 statistical relationships with plumage colour of blue tits in 52 studies. However, of the approximately 1000 main‐effect relationships from the 48 studies that are candidates for inclusion in this meta‐analysis, more than 400 were reported without details of strength and direction. Circumstantial evidence suggests that an unknown number of other estimated effects remain unpublished. Missing information is a substantial barrier to interpretation of these papers and to meta‐analytic synthesis. Examination and analysis of funnel plots indicated that unpublished effects may be a biased sample of all effects, especially for comparisons of plumage colour to age and individual quality, and possibly also to measures of mate choice. Further, type I error was likely elevated by the large number of statistical comparisons evaluated, the frequent use of iterative model‐building procedures, and a willingness to interpret a wide variety of results as support for a hypothesis. Type I errors were made more problematic because blue tit plumage researchers only rarely have attempted to replicate important findings in their own work or that of others. Replication is essential to drawing robust scientific conclusions, especially in probabilistic systems with moderate to weak effects or a likelihood of bias. Last, researchers studying blue tit plumage have often developed ad hoc explanations for deviations of results from their predictions. Revising hypotheses in light of data is appropriate, but these revised hypotheses were rarely tested with new data. The only highly robust conclusion supported by meta‐analysis is that male blue tits have plumage that reflects more light in the ultraviolet and yellow wavelengths than the plumage of females. Various other effects, including condition‐dependence of plumage colour expression and a tendency for females to adjust the sex ratio of their offspring in response to male colour, remain uncertain. These obstacles to progress in the blue tit plumage literature are likely common in evolutionary biology, and so I recommend changes to incentive structures which may improve progress towards scientific understanding in this discipline.     

Carotenoid‐based plumage colouration is predicted by age and parasites in the male European serin

A fundamental assumption of theories on the evolution of sexual signals is that they should be costly to produce in order to honestly signal the quality of the sender. The expression of carotenoid‐based plumage signals is considered to be condition‐dependent, due to the role of carotenoids functioning as pigments and as health modulators. We assessed carotenoid‐based plumage colouration in relation to male condition in a free living population of male European serins Serinus serinus during the breeding season. Male serins were trapped for morphometric and colouration measurements, during a four‐year field study, in order to evaluate the signalling value of colouration in relation to body condition and parasites level. We compared two different forms of colour quantification based on spectral data – the most commonly used tristimulus colour variables and physiological models of avian colour vision – and found that they were highly correlated for this species. We investigated the signalling value of male plumage colouration and it was found to be related to age and ectoparasite load. Plumage double cone and patch size were negatively related to parasites level, whereas SWS ratio was positively related to parasites and age. Colouration was also related with the time since moult. Our results indicate that the colour expression of serin's plumage is age dependent and is related, in complex ways, with the ability to cope with parasitic infection.