Plumage Variation Research Articles

Comparing plumage colour measurements obtained directly from live birds and from collected feathers: the case of the great tit Parus major

Birds frequently display a colourful plumage which is important both in inter and intraespecific communication, and either in sexual and social contexts. In last years some methodologies have been developed to, analyse plumage coloration, but the use of the spectrometers has been particularly important for UV range. Measurement of plumage coloration with the spectrometer may be taken directly on the bird or, alternatively by collecting some feathers and measuring them later in the laboratory. However, few is known about the reliability of measures obtained from feathers and whether these are really representative of plumage coloration. We tested this assumption analysing measurements of carotenoids‐based coloration components (lightness, chroma and hue) and lutein peak of the yellow breast of the great tit Parus major. We used two spectrometers (Ocean optics and Minolta) which calculate differently the colour components. Our results showed that direct measurement of bird was highly repeatable to determine lightness, chroma and hue for both spectrometers. Similar results we found for collected feathers procedure for both devices. Collected feathers provided high representative measurements of colour values with Minolta spectrometer. Lightness was highly repeatable when we used Ocean optic spectrometer, but chroma and hue were moderate. Lutein peak was also highly repeatable in all cases. The number of feathers used to measure plumage coloration in collected feathers procedure strongly influenced values of colour plumage variables. In general, values of lightness, chroma and hue stabilised when more than 10–15 feathers were used although we found slight differences between spectrometers. However, only four feathers were needed for lutein peak. Thus, our results stress the need to use a minimum number of feathers in measuring plumage coloration from collected feathers.

Sequence variation in the coding region of the melanocortin-1 receptor gene (MC1R) is not associated with plumage variation in the blue-crowned manakin (Lepidothrix coronata)

Avian plumage traits are the targets of both natural and sexual selection. Consequently, genetic changes resulting in plumage variation among closely related taxa might represent important evolutionary events. The molecular basis of such differences, however, is unknown in most cases. Sequence variation in the melanocortin-1 receptor gene (MC1R) is associated with melanistic phenotypes in many vertebrate taxa, including several avian species. The blue-crowned manakin (Lepidothrix coronata), a widespread, sexually dichromatic passerine, exhibits striking geographic variation in male plumage colour across its range in southern Central America and western Amazonia. Northern males are black with brilliant blue crowns whereas southern males are green with lighter blue crowns. We sequenced 810 bp of the MC1R coding region in 23 individuals spanning the range of male plumage variation. The only variable sites we detected among L. coronata sequences were four synonymous substitutions, none of which were strictly associated with either plumage type. Similarly, comparative analyses showed that L. coronata sequences were monomorphic at the three amino acid sites hypothesized to be functionally important in other birds. These results demonstrate that genes other than MC1R underlie melanic plumage polymorphism in blue-crowned manakins.

Interspecific variation in the use of carotenoid‐based coloration in birds: diet, life history and phylogeny

Birds show striking interspecific variation in their use of carotenoid-based coloration. Theory predicts that the use of carotenoids for coloration is closely associated with the availability of carotenoids in the diet but, although this prediction has been supported in single-species studies and those using small numbers of closely related species, there have been no broad-scale quantitative tests of the link between carotenoid coloration and diet. Here we test for such a link using modern comparative methods, a database on 140 families of birds and two alternative avian phylogenies. We show that carotenoid pigmentation is more common in the bare parts (legs, bill and skin) than in plumage, and that yellow coloration is more common than red. We also show that there is no simple, general association between the availability of carotenoids in the diet and the overall use of carotenoid-based coloration. However, when we look at plumage coloration separately from bare part coloration, we find there is a robust and significant association between diet and plumage coloration, but not between diet and bare part coloration. Similarly, when we look at yellow and red plumage colours separately, we find that the association between diet and coloration is typically stronger for red coloration than it is for yellow coloration. Finally, when we build multivariate models to explain variation in each type of carotenoid-based coloration we find that a variety of life history and ecological factors are associated with different aspects of coloration, with dietary carotenoids only being a consistent significant factor in the case of variation in plumage. All of these results remain qualitatively unchanged irrespective of the phylogeny used in the analyses, although in some cases the precise life history and ecological variables included in the multivariate models do vary. Taken together, these results indicate that the predicted link between carotenoid coloration and diet is idiosyncratic rather than general, being strongest with respect to plumage colours and weakest for bare part coloration. We therefore suggest that, although the carotenoid-based bird plumage may a good model for diet-mediated signalling, the use of carotenoids in bare part pigmentation may have a very different functional basis and may be more strongly influenced by genetic and physiological mechanisms, which currently remain relatively understudied.

A comparison of age, size, and health of House Finches captured with two trapping methods

House Finches are being increasingly studied because of their variation in male plumage, evolving migration, and susceptibility to mycoplasmal conjunctivitis. Researchers traditionally use two methods for capturing House Finches: a walk-in hardware mesh cage around a bird feeder and mist nets placed next to lure feeders. However, because one method relies on birds' willingness to enter a foreign structure to obtain food, while the other captures them while flying, these methods may not sample the same subset of the House Finch population. This possibility could have serious consequences for studies of plumage coloration, where sex and age ratios are important; for studies of migration, where measures of wing lengths reflect migratory ability; and for studies of mycoplasmal infections, where disease state and measures of health are important. I used data from a long-term monitoring project of House Finches that employs both capture techniques to test if any attributes of House Finches differed between mist-netted and cage-trapped birds. Of 1173 House Finch captures over 3 yr, I found no trap-related difference in the proportion of birds with conjunctivitis, nor in the proportions of males or in the ratios of molting versus non-molting birds. There was also no difference in House Finch tarsus lengths or weights between capture methods. However, a larger proportion of young birds were captured in cage traps, and wing lengths were greater in birds captured with mist nets. I conclude that in general, cage traps and mist nets sample similar subsets of House Finches, but that researchers should view their trapping data with these inherent age and size biases in mind.

Ultraviolet Degradation in Carotenoid Patches: Live Versus Museum Specimens of Wood Warblers (Parulidae)

AbstractAccurate assessment of color is essential in testing the adaptive significance of color variation in avian plumage. Over the past decade, use of objective methods for assessing color has increased, with particular emphasis on ultraviolet (UV) wavelengths. Researchers have used various source materials, most notably museum specimens, to extend or represent color measurements of individuals in natural populations. Here, we address whether the colors seen in museum specimens accurately represent the colors seen in natural populations. We focus on UV wavelengths and carotenoid-derived colors across 10 species of wood-warblers (Parulidae). Our results indicate an uneven decrease in brightness across the color spectrum, with greater relative decrease in shorter wavelengths in museum specimens. That decrease leads to differences in both hue and chroma between living and museum specimens. The difference from live specimens appears to increase with the museum specimen's age. Our results suggest that caution is needed when using data from museum specimens to test hypotheses on plumage coloration, particularly those involving communication.Degradación Ultravioleta en Parches de Carotenoides: Especímenes Vivos versus Especímenes de Museo de Especies de la Familia Parulidae

Prevalence and genetic diversity of Bacillus licheniformis in avian plumage

Bacillus licheniformis, a soil bacterium capable of degrading the b-keratin in feathers, is present in the plumage of some wild-caught birds, but the published carriage rate is quite low. Microbial degradation could be a selective agent leading to the evolution of molt and plumage pigmentation, but we hypothesized that for B. licheniformis to have played an important role in avian evolution, it is likely to occur more widely in bird populations than previously reported. We sampled the plumage of 461 wild-caught birds of eight species. We designed a selective and differential culture method to isolate bacteria with the potential to degrade feathers. Putative feather-degrading bacteria were isolated from 21-59% of the individuals of each of the species tested, for an average carriage rate of 39%. 16S rRNA (rrnA) sequencing of 98 of these bacterial isolates indicated that 69% were Bacillus lichenformis, suggesting that the prevalence of this feather-degrading bacterium is 4 3 higher than previously reported. We also hypothesized that interspecific variation in avian plumage, behavior, and habitat may have led to the evolution of host-specific B. licheniformis strains. Fingerprinting of B. licheniformis isolated from Northern Saw-whet Owls (Aegolius acadicus) and Gray Catbirds (Dumetella carolinensis) using REP-PCR demonstrated that for nine owls, one individual carried four different strains and eight individuals carried only one strain. Of 20 catbirds, there was a single strain found on nine birds, but four carried two different strains each. SINOPSIS. Prevalencia y diversidad genetica de Bacillus licheniformis en el plumaje de aves

CRYPTIC DICHROMATISM AND SEASONAL COLOR VARIATION IN THE DIADEMED TANAGER

Abstract We studied the patterns of sexual dichromatism and seasonal variation in plumage color in the Diademed Tanager (Stephanophorus diadematus), a species previously considered devoid of variation in adult plumage. The general coloration of this species is dark blue-violet, with a white-blue and red crown. Plumage reflectance of seven body regions from 33 study skins belonging to adults of both sexes was measured. Reflectance values were used in a principal components analysis (PCA) and hue, short-wave chroma, and UV chroma were also measured directly on the spectra. Both PCA factor scores and these latter variables were subjected to two-way ANCOVAs with sex and season as main factors and the year of capture as a covariate. We found that crowns of males were significantly brighter than those of females. In addition, the nape, chest, and belly showed significant differences in spectral shape, with relatively greater short-wave reflectance and less long-wave reflectance in males than in females. Althoug...

ULTRAVIOLET DEGRADATION IN CAROTENOID PATCHES: LIVE VERSUS MUSEUM SPECIMENS OF WOOD WARBLERS (PARULIDAE)

Accurate assessment of color is essential in testing the adaptive significance of color variation in avian plumage. Over the past decade, use of objective methods for assessing color has increased, with particular emphasis on ultraviolet (UV) wavelengths. Researchers have used various source materials, most notably museum specimens, to extend or represent color measurements of individuals in natural populations. Here, we address whether the colors seen in museum specimens accurately represent the colors seen in natural populations. We focus on UV wavelengths and carotenoid-derived colors across 10 species of wood-warblers (Parulidae). Our results indicate an uneven decrease in brightness across the color spectrum, with greater relative decrease in shorter wavelengths in museum specimens. That decrease leads to differences in both hue and chroma between living and museum specimens. The difference from live specimens appears to increase with the museum specimen's age. Our results suggest that caution is needed when using data from museum specimens to test hypotheses on plumage coloration, particularly those involving communication. Degradación Ultravioleta en Parches de Carotenoides: Especímenes Vivos versus Especímenes de Museo de Especies de la Familia Parulidae

Carotenoid-based plumage coloration predicts resistance to a novel parasite in the house finch

The Hamilton-Zuk hypothesis proposes that the bright colours displayed by many species of birds serve as signals of individual resistance to parasites. Despite the popularity of this hypothesis, only one previous study has tested whether plumage coloration predicts how individuals respond to a disease challenge. We inoculated 24 male house finches (Carpodacus mexicanus) of variable plumage hue with a novel bacterial pathogen, Mycoplasma gallicepticum (MG). We found no relationship between plumage hue and time to first symptoms following inoculation, but we found a significant negative relationship between plumage hue and clearance of disease: males with redder plumage cleared MG infection significantly better than did males with yellower plumage. The hue of carotenoid-based plumage coloration has been shown to be a primary criterion in female mate choice in the house finch. These observations suggest that one benefit to females for choosing redder males is obtaining mates with better resistance to parasites.

Ultraviolet plumage reflectance distinguishes sibling bird species

Realistic studies of plumage color need to consider that many birds can see near-UV light, which normal humans cannot perceive. Although previous investigations have revealed that UV-based plumage reflectance is an important component of various intraspecific social signals, the contribution of UV signals to inter-specific divergence and speciation in birds remains largely unexplored. I describe an avian example of an interspecific phenomenon in which related sympatric species that appear similar to humans (sibling species) differ dramatically in the UV. Both UV video images and physical reflectance spectra indicate that the dorsal plumage of the tanager Anisognathus notabilis has a strong UV-limited reflectance band that readily distinguishes this species from its sibling congener Anisognathus flavinuchus. The main human-visible distinction between A. notabilis (olive back) and coexisting A. flavinuchus (black back) also occurs among different geographic populations of A. flavinuchus. Notably, however, olive- and black-backed taxa interbreed (differentiated populations of A. flavinuchus) unless the additional UV distinction is present (A. notabilis vs. A. flavinuchus). Thus, UV-based reflectance can be an essential component of plumage divergence that relates to reproductive isolation, a key attribute of biological species.

HABITAT SELECTION, ACOUSTIC ADAPTATION, AND THE EVOLUTION OF REPRODUCTIVE ISOLATION

We examined barriers to gene flow in a hybrid zone of two subspecies of the song sparrow (Melospiza melodia). We focused on how mating signals and mate choice changed along an environmental gradient and gathered data on the morphology, genetics, ecology, and behavior across the zone. Melospiza m. heermanni of the Pacific slope of California and M. m. fallax of the Sonoran Desert, each distinct in plumage, meet across a steep environmental gradient in southeastern California. Although both subspecies occur in riparian habitat, their occupied habitat differs structurally, the former subspecies occurring in areas with denser understory and greater vertical heterogeneity. Song elements varied concomitantly, as predicted by the acoustic adaptation hypothesis, with heermanni having lower-pitched, more widely spaced elements. Females of both subspecies responded more strongly to homotypic than heterotypic song, and addition of subspecific plumage cues increased response if song was homotypic but not if heterotypic. Females thus assess multiple male traits, weighing song more heavily. Males of both subspecies showed significantly greater agonistic response to homotypic song. Microsatellite variation is correlated significantly with plumage variation across the zone and suggests limited gene flow between the taxa. The association of song and plumage with the environment and in turn with assortative mating suggests a means by which reproductive isolation may evolve or be maintained in hybrid zones.

Achromatic plumage reflectance predicts reproductive success in male black-capped chickadees

The size of achromatic (black, white, gray) plumage patches serves as a male status signal in many species of birds, but variation in the colors of these patches has received little attention. We assessed the relation between achromatic plumage reflectance, dominance rank, body condition, and reproductive success in male black-capped chickadees, Poecile atricapillus. We measured plumage reflectance for five body regions of 40 male chickadees in late winter and monitored these males throughout the following breeding season to determine whether they survived to breed, whether they successfully paired, whether their partner laid eggs, and both their apparent and realized reproductive success. As expected from past studies, a male's dominance rank significantly predicted whether his partner laid eggs. However, only achromatic plumage reflectance significantly predicted other measures of male reproductive performance. Among males who fledged at least one offspring, both the brightness of white plumage regions and the UV-chroma of melanin-based plumage regions were significant predictors of the proportion of within-pair young in their nests. When we consider all males we measured, assigning zero values to males who failed to sire any offspring, the UV-chroma of melanin-based plumage regions was a significant predictor of realized reproductive success. Bib size was also related to male realized reproductive success. Our findings suggest that individual variation in achromatic plumage may play an important role in sexual signaling in chickadees.

Offspring sex ratios correlate with pair–male condition in a cooperatively breeding fairy–wren

We examined sex allocation patterns in island and mainland populations of cooperatively breeding white-winged fairy-wrens. The marked differences in social structure between island and mainland populations, in addition to dramatic plumage variation among males both within and between populations, provided a unique situation in which we could investigate different predictions from sex allocation theory in a single species. First, we test the repayment (local resource enhancement) hypothesis by asking whether females biased offspring sex ratios in relation to the assistance they derived from helpers. Second, we test the male quality (attractiveness) hypothesis, which suggests that females mated to attractive high-quality males should bias offspring sex ratios in favor of males. Finally, we test the idea that females in good condition should bias offspring sex ratios toward males because they are able to allocate more resources to offspring, whereas females in poor condition should have increased benefits from producing more female offspring (Trivers-Willard hypothesis). We used molecular sexing techniques to assess total offspring sex ratios of 86 breeding pairs over 2 years. Both offspring and first brood sex ratios were correlated with the pair-male’s body condition such that females increased the proportion of males in their brood in relation to the body condition (mass corrected for body size) of their social partner. This relation was both significant and remarkably similar in both years of our study and in both island and mainland populations. Although confidence of paternity can be low in this and other fairy-wren species, we show how this finding might be consistent with the male quality (attractiveness) hypothesis with respect to male condition. There was no support for the repayment hypothesis; the presence of helpers had no effect on offspring sex ratios. There was weak support for both the male quality (attractiveness) hypothesis with respect to plumage color and the maternal condition hypothesis, but their influence on offspring sex ratios was negligible after controlling for the effects of pair-male condition. Key words: sex allocation, offspring sex ratio, parental condition, cooperative breeding, plumage coloration. [BehavEcol]

Systematics and Biogeography of Double-Collared Sunbirds From the Eastern Arc Mountains, Tanzania

AbstractThe double-collared sunbirds of the Eastern Arc Mountains of Tanzania and southeastern Kenya are characterized by regional variation in morphology and plumage. That variation has resulted in considerable dispute over their taxonomic status and delineation of range boundaries. It has been suggested that Moreau's Sunbird (Nectarinia Moreaui) is an atypical phenotype that has arisen from a hybridization event between the more widely distributed Eastern Double-collared Sunbird (N. mediocris) and the narrowly distributed Loveridge's Sunbird (N. loveridgei). A discriminant analysis of six standard morphological characters indicates that Moreau's Sunbird is intermediate in shape and size between the Eastern Double-collared and Loveridge's sunbirds. There is greater overlap between female Moreau's and Eastern Double-collared sunbirds than between males; Loveridge's Sunbird shows little overlap with the other taxa. Discrete plumage characters separate all three taxa. Molecular analyses of 728 base pairs of mitochondrial DNA (NADH3 and control region) suggest that Moreau's Sunbird is a valid taxon and the sister species to Loveridge's Sunbird. Eastern Double-collared Sunbird haplotypes can be divided into three distinct clades, separated from each other by substantial genetic divergence (approximately 8–10% sequence divergence). We propose species status for each of those clades and suggest the following three taxa: N. mediocris Shelley 1855, N. usambarica Gröte 1922, and N. fuelleborni Reichenow 1899. Finally, we propose a biogeographical hypothesis of speciation events within the N. mediocris species complex.

HABITAT SELECTION, ACOUSTIC ADAPTATION, AND THE EVOLUTION OF REPRODUCTIVE ISOLATION

We examined barriers to gene flow in a hybrid zone of two subspecies of the song sparrow (Melospiza melodia). We focused on how mating signals and mate choice changed along an environmental gradient and gathered data on the morphology, genetics, ecology, and behavior across the zone. Melospiza m. heermanni of the Pacific slope of California and M. m. fallax of the Sonoran Desert, each distinct in plumage, meet across a steep environmental gradient in southeastern California. Although both subspecies occur in riparian habitat, their occupied habitat differs structurally, the former subspecies occurring in areas with denser understory and greater vertical heterogeneity. Song elements varied concomitantly, as predicted by the acoustic adaptation hypothesis, with heermanni having lower-pitched, more widely spaced elements. Females of both subspecies responded more strongly to homotypic than heterotypic song, and addition of subspecific plumage cues increased response if song was homotypic but not if heterotypic. Females thus assess multiple male traits, weighing song more heavily. Males of both subspecies showed significantly greater agonistic response to homotypic song. Microsatellite variation is correlated significantly with plumage variation across the zone and suggests limited gene flow between the taxa. The association of song and plumage with the environment and in turn with assortative mating suggests a means by which reproductive isolation may evolve or be maintained in hybrid zones.

SYSTEMATICS AND BIOGEOGRAPHY OF DOUBLE-COLLARED SUNBIRDS FROM THE EASTERN ARC MOUNTAINS, TANZANIA

Abstract The double-collared sunbirds of the Eastern Arc Mountains of Tanzania and southeastern Kenya are characterized by regional variation in morphology and plumage. That variation has resulted in considerable dispute over their taxonomic status and delineation of range boundaries. It has been suggested that Moreau's Sunbird (Nectarinia Moreaui) is an atypical phenotype that has arisen from a hybridization event between the more widely distributed Eastern Double-collared Sunbird (N. mediocris) and the narrowly distributed Loveridge's Sunbird (N. loveridgei). A discriminant analysis of six standard morphological characters indicates that Moreau's Sunbird is intermediate in shape and size between the Eastern Double-collared and Loveridge's sunbirds. There is greater overlap between female Moreau's and Eastern Double-collared sunbirds than between males; Loveridge's Sunbird shows little overlap with the other taxa. Discrete plumage characters separate all three taxa. Molecular analyses of 728 base pairs o...

Dark wings of desire

Birds vary enormously in their use of the pigment melanin to colour their plumage but the variation between species and between sexes has been a puzzle to researchers. New work on the plovers, a diverse group of mostly ground-nesting birds which show highly diverse use of melanin, suggests that sexual selection during aerial displays is one cause of the pigmentation.Veronika Bokony and colleagues at the Szent Istvan University in Budapest and at the University of Bath, UK, report in the Proceedings of the Royal Society B in London (published online) a comparison of the wide variation in melanin-coloured plumage between different species of plover and other aspects of their lifestyle.The authors hypothesised that melanin-coloured plumage may be more common in species where males carry out aerial courtship displays compared with those using ground-based courtships. And the plovers include species that use both courtship behaviours. The authors thought that black plumage may help enhance the silhouette of the bird against the sky during an aerial display and thus increase the attention of ground-based females during the display.The results suggest that this is indeed the case. Birds with ground-based displays show much less melanin-coloured plumage compared with the males of species carrying out aerial displays. They looked at whether melanin coloration might help with camouflage or in displays to defend territories but found no link between melanin coloration and these two lifestyle aspects compared to the link with aerobatic courtship displays by the males.“Taken together, our results are most consistent with the sexual selection hypothesis, and suggest that melaninised plumage has evolved to enhance the aerial display of male plovers,” the authors report.Cutting an aerial dash, in black, seems to be the plumage key to attracting mates in this group of plovers at least.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Unmelanized plumage patterns in Old World leaf warblers do not correspond to sequence variation at the melanocortin-1 receptor locus (MC1R).

Evolutionary changes in patterns and coloration of plumage are likely to represent a major mechanism for speciation among birds, yet the molecular basis for such changes remains poorly understood. Recently much attention has focused on the melanocortin-1 receptor (MC1R) as a candidate locus for determining the level and extent of epidermal melanin deposition. We tested the hypothesis that MC1R sequence variation is associated with interspecific variation in unmelanized plumage pattern elements in Old World leaf warblers (genus Phylloscopus). This genus is characterized by a variety of plumage patterns that nonetheless vary along similar lines. Species vary in the presence or absence of pale (unmelanized) pattern elements against a dark background, and these patterns are used in species recognition and courtship. We sequenced most of the MC1R coding region for eight Phylloscopus species, representing the full range of plumage patterns found in this genus. Although MC1R sequence varied among species, this variation was not related to melanin-based plumage variation. Rather, evolution of this locus in these birds appears to be conservative. Ratios of nonsynonymous to synonymous substitutions (dN/dS) were consistently low, suggesting that strong purifying selection has operated at this locus, and likelihood ratio testing revealed no evidence of variable selective pressures among lineages or across codons. Adaptive evolution at MC1R may be constrained by the adaptive importance of plumage pattern elements in this genus.

Variable plumage and bare part colouration in the Brown Falcon, Falco berigora: the influence of age and sex

The Brown Falcon, Falco berigora, is one of Australasia's most common raptors, yet considerable confusion remains over the influence of geography, age and sex on plumage and bare part colouration in this species. To address this issue, 160 immature and adult falcons from an individually marked, closely monitored population were examined. In contrast to previous studies, all were of known sex, age-group and part of the resident population or their offspring. Adult males had significantly lighter upperpart, cap, ventral and underwing covert plumage in comparison with other birds, closely resembling what has previously been described as a ‘rufous morph’. Immature females were significantly darker than other ages and sexes in upperpart and underwing covert plumage, resembling descriptions of ‘dark morphs’. In contrast, plumage of immature males and adult females tended to be similar and intermediate between these extremes, resembling the ‘brown morph’. The buff-tinged, not white, ventral plumage and darker underwing covert plumage of immature males separated them from adult females. Cere and orbital ring colour also differed with sex and age: immature females had the dullest facial bare parts and adult males the brightest, adult females and immature males again being intermediate between the two. The results indicate that most variation in plumage and facial bare part colouration observed in the population could be attributed to age and sex differences as opposed to racial clines or the existence of colour morphs. Moreover, the brighter colours of adult falcons may function as honest signals of quality.

Variation in plumage, molt, and morphology of the Whiskered Auklet (Aethia pygmaea) in Alaska

Abstract We studied molt and size variation in Whiskered Auklets collected at sea in August from the Aleutian Islands in 1992 and 1993. We evaluated size differences from external and skeletal measurements. Adults were molting extensively in August, indicating that molt began in July. Primaries 1–5 had been completely replaced, while primaries 6–8 were in various stages of replacement, and primaries 9 and 10 were old in most birds. We also found that juveniles were not molting. This pattern is similar to other species of small auklets where breeding and molt in adults overlap, but juveniles do not molt until the following summer. This suggests that Whiskered Auklets are subjected to similar ecological constraints as other auklets. We provide the first skeletal measurements of Whiskered Auklets and some new external measurements. Results of statistical analyses indicate that there is no sexual dimorphism in adults. A small sample of juveniles suggests that they are similar in size to adults.