Bill Color Research Articles

Morphological characterization with special reference to color variations in domestic geese (Anser anser domesticus)

A study was planned to record and document the morphological characteristics with special reference to color variations in domestic geese. Knob, dewlap and paunch were present in 44.71, 3.07 and 13.59 % of birds respectively. No curled feathers in the tail were seen in any of the geese studied. Ample color variation was observed in the plumage, eye and bill but not in shanks. Color of the plumage along the body, head, neck, abdomen, and across the wings varied from all cinnamon to all white through all intermediate gradations. Bill color also varied from all black to all yellow through all intermediates. Color of eyes was either grey or brown. No variation was noted in the shank color. It was orange in adults and yellow in goslings. The peculiar colour pattern and markings in domestic geese might be useful in identification of individual birds as is done in horses. Sexual dimorphism on the basis of plumage color and presence of curved tail feathers was absent.

Phenotypic Variation in Mangrove Cuckoo (Coccyzus minor) across Its Geographic Range.

Mangrove Cuckoo (Coccyzus minor) exhibits substantial phenotypic variation across its geographic range, but the significance of this variation for taxonomy remains unresolved. Using measurements of bill size and ventral color recorded from 274 museum specimens, I found that variation in these traits was clinal. No named subspecies was reciprocally diagnosable from all others, and none was distinguishable from the nominate form, such that previously recognized subspecific distinctions are invalid. Greatest differences in phenotype occurred between populations in Florida, the Bahamas, and the Greater Antilles–characteristically small-billed–and those in the Lesser Antilles, which had larger bills. Phenotypically intermediate individuals on the geographically intermediate islands of Barbuda and Antigua linked these two extremes. Individuals intermediate in bill size and color also characterized populations from throughout the remainder of the range in northern South America and Middle America. Mechanisms maintaining the fairly pronounced phenotypic differences between nearby populations of Greater and Lesser Antillean birds are unknown, yet the geographic proximity of these populations suggests that they probably persist despite occasional gene flow, and may be adaptive.

Bill color characteristics and body mass of the great tit (Parus major) nestling

This study was conducted to examine the bill color and body mass of great tit (Parus major) nestlings in artificial nest boxes. In this study, the nestlings with yellow bills had a higher body mass on the second and eighth day after hatching. Moreover, the brightness values of the color of the bill on the eighth day after hatching were negatively correlated with the body mass of the chicks. Our experiment shows that the color of the bill of the nestling could accurately signal the quality of the chick. Moreover, carotenoid-based colors play an important role in avian communication. Study of carotenoid-based colors in the great tit would be required in the future.

Carotenoid-based bill coloration functions as a social, not sexual, signal in songbirds (Aves: Passeriformes).

Many animals use coloration to communicate with other individuals. Although the signalling role of avian plumage colour is relatively well studied, there has been much less research on coloration in avian bare parts. However, bare parts could be highly informative signals as they can show rapid changes in coloration. We measured bill colour (a ubiquitous bare part) in over 1600 passerine species and tested whether interspecific variation in carotenoid-based coloration is consistent with signalling to potential mates or signalling to potential rivals in a competitive context. Our results suggest that carotenoid bill coloration primarily evolved as a signal of dominance, as this type of coloration is more common in species that live in social groups in the nonbreeding season, and species that nest in colonies; two socio-ecological conditions that promote frequent agonistic interactions with numerous and/or unfamiliar individuals. Additionally, our study suggests that carotenoid bill coloration is independent of the intensity of past sexual selection, as it is not related to either sexual dichromatism or sexual size dimorphism. These results pose a significant challenge to the conventional view that carotenoid-based avian coloration has evolved as a developmentally costly, condition-dependent sexual signal. We also suggest that bare part ornamentation may often signal different information than plumage ornaments.

Juvenile sexual dimorphism, dichromatism and condition-dependent signaling in a bird species with early pair bonds

AbstractSexual selection in juvenile vertebrates is a rare and seldom studied phenomenon. Bearded Reedlings are passerines that form stable, life-long pair bonds within a few weeks after fledging. We investigated the degree to which juvenile Bearded Reedlings are sexually dimorphic and whether they possess condition-dependent ornaments. We found significant intersexual differences in the bill reflectance, reflectance and size of eumelanin-based plumage traits (lore and back patch) and morphological traits. Females that were in better body condition had longer tails and bills with greater red chroma, and lore size was negatively related to the occurrence of chewing lice. In males, body condition was positively related to melanic back patch length. Moreover, a positive relationship between bill color and feather mite load in males suggests a symbiotic, rather than parasitic, relationship. Our study provides the first evidence that sexually dimorphic traits in immature birds with pair bonds have the potential to signal condition and resistance to parasites.

A practical framework to analyze variation in animal colors using visual models

To study biologically relevant variation in visual signals, these need to be assessed in relation to the sensory abilities of receivers. For the study of colors, reflectance spectrometry has been the method of choice, but analyses of reflectance spectra present challenges that hamper our understanding of color variation. Among these are computing meaningful color variables and interpreting their biological relevance. Here, we suggest how to overcome the limitations of commonly used approaches. We describe how to use psychophysical visual models to assess chromatic variation in the visual space of animals. This approach consists of 1) obtaining cone quantum catches from reflectance spectra, 2) transforming these into visual space coordinates where Euclidean distances reflect perceptual distances, 3) summarizing variation in visual space using principal component analysis (PCA) maintaining original perceptual units, and 4) interpreting the axes of chromatic variation (PC) based on their loadings and relative and absolute levels of chromatic variation. We illustrate this approach by comparing it to traditional color indices (hue and saturation) and PCA computed directly on reflectance spectra, using 2 examples: 1) determining the biological relevance of correlations between bill coloration and male quality in mallards and 2) assessing the success of experimental color manipulations in blue tits. In both cases, re-analyzing the data suggests different interpretations. This approach provides a simple way of objectively summarizing chromatic variation and interpreting the magnitude of biologically relevant effects. We provide R scripts to carry out computations and recommendations on how to report results to make data comparable between studies.

An assessment of the developmental toxicity of BDE-99 in the European starling using an integrated laboratory and field approach.

Developmental exposure of wildlife to anthropogenic contaminants can have long-term effects that are difficult to assess in field monitoring studies, and may not be evident in laboratory studies that lack ecological components. The objective of this study was to assess the long-term effects of early exposure to contaminants under ecological conditions in a model passerine species, the European starling (Sturnus vulgaris). We selected 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) as a representative contaminant, as it is one of the major constituents of the commercial penta-BDE flame retardant mixture, and has been reported in avian egg and tissue samples worldwide. We developed a novel approach to assess the developmental toxicity of BDE-99 in starlings by combining aspects of laboratory and field studies. We dosed free-living nestlings living in natural broods in the field with environmentally relevant concentrations of BDE-99 (0-173.8 ng/g bw/day) for the duration of the nesting cycle. To simulate monitoring of long-term effects we brought birds into captivity just prior to fledging and used photoperiod manipulations to induce reproductive development. We assessed a range of physiological and development measures such as hematocrit, oxidative stress, thyroid hormones, neuroanatomy, growth, molt rate, bill color, and testes development. We found some evidence of thyroid hormone disruption, but there were no effects on any other measures of physiology or development. The European starling could serve as a valuable model species for assessing early exposure and long-term effects of anthropogenic contaminants in terrestrial wildlife using this combined field/laboratory approach.

Blood parasite infection differentially relates to carotenoid-based plumage and bill color in the American goldfinch.

Male and female American goldfinches (Spinus tristis) express condition-dependent carotenoid-based plumage and bill coloration. Plumage color is relatively static, as pigments incorporated into feathers during the spring molt cannot be mobilized thereafter. In contrast, bill color is dynamic, reflecting changes in condition over short time periods. Previous studies have shown that male and female ornaments, though similar in expression, are differentially related to measures of immunocompetence, suggesting that the relationship between ornamentation and parasite infection may differ between the sexes. In this study, we evaluate the relationship between condition-dependent ornamentation (plumage and bill color) and blood parasite infection in male and female American goldfinches. We captured goldfinches after completion of the pre-alternate molt and prior to the onset of nesting and assessed prevalence of Trypanosoma parasites via blood smears. Plumage color strongly predicted trypanosome infection: Birds with more colorful plumage were less likely to present infections. In contrast, we detected no relationship between infection and bill color, which in other studies has been shown to dynamically reflect current condition. Sex did not affect the relationship between infection status and either ornament. Together, these results suggest that physiological pathways linking carotenoid ornamentation and infection may vary even within a single species.

Same trait, different receiver response: unlike females, male American goldfinches do not signal status with bill colour

In species in which both sexes have similar ornamentation, the ornaments often function as sexual or social signals in both sexes. However, males and females may use ornaments in different signalling contexts. We previously demonstrated that carotenoid-based bill colour of female American goldfinches, Spinus tristis, functions as a signal of status during intrasexual, but not intersexual, competition. Here we test whether male bill colour functions as a competitive status signal during both intra- and intersexual contests. We tested whether focal males and females avoided feeding adjacent to taxidermic male models as a function of the models’ experimentally altered bill colour. We additionally tested whether male bill colour functions as a mate choice signal by presenting females with a choice of two live males with experimentally altered bill colour. In the status signal experiment, neither focal males nor females avoided male models with more colourful bills, as was predicted by the status-signalling hypothesis. These results indicate that male bill coloration does not function as a signal of competitive status and that the signal function of male bill colour does not parallel that of female bill colour. In our mate choice experiment, females showed no preference for male bill colour, suggesting that male bill colour may have some yet untested signalling function or that male bill colour may no longer be under selection. Our findings suggest that selection can lead to different signalling strategies in males and females, even in species that express mutual ornamentation.

Black-browed Albatross Thalassarche melanophris primary moult timing in the fourth prebasic moult

The aging of immature Black-browed Albatrosses Thalassarche melanophris is reasonably well understood using a combination of primary moult sequence and timing (see Appendix), and progression in plumage aspect (bill colour and pattern, head and neck markings, and whitening of the underwing-coverts). The initial work of Prince et al. (1993) and Prince & Rodwell (1994) studied ringed (known-age) non- breeding Black-browed Albatrosses visiting a study colony on Bird Island, South Georgia between December 1989 and February 1990. Adding to this, Bugoni & Furness (2009) examined and photographed a sample of 33 birds captured at sea off the Brazilian coast in February to June 2006 and July to September 2007. Howell (2010, 2012) provided a number of at-sea photographs illustrating many of the immature age groups. These studies are important to understanding the impact of bycatch on different age groups, and to aging and identification for field birders.

Where are Western Bounds of Area S. h. ?

We reported about several common terns with dark bill (subspecies Sterna hirundo minussensis and S. h. longipennis) in the Lower Ob region of Western Siberia, including nesting of the Central Siberian tern here. The ratio of terns with a dark bill and nominate color was about 8 to 1. Our findings change the previous understanding of areas of the distribution of those subspecies.

Honesty of a dynamic female aggressive status signal: baseline testosterone relates to bill color in female American goldfinches

Status signals are linked to fighting ability and enable competitors to gain access to resources without risking injury in aggressive combat. The relationship between testosterone (T), a hormone that mediates aggression, and signals of status is well studied in males, but little is known about the relationship between T and female signals of status. Female and male American goldfinches Spinus tristis express a dynamic carotenoid‐based orange bill color during the breeding season and previous work has demonstrated that females use orange bill color to communicate competitive ability during intrasexual competition. We test the hypothesis that female bill color reflects baseline T, which would allow receivers to directly assess a competitor's aggressive potential. We found a positive relationship between T and bill coloration in females, indicating that bill color has the ability to signal female competitive status. This finding is consistent with the hypothesis that female bill color is a reliable signal of fighting ability, and indicates that females, like males, may use coloration to signal their hormonally mediated aggressive potential.

Incubation shifts of northern fulmars Fulmarus glacialis in the Canadian high Arctic determined by digital photography

Determining the incubation pattern of northern fulmars (Fulmarus glacialis) at Canadian Arctic colonies is difficult, in part due to challenges with accessing nests and due, in part, to similarities in colour morphs which can be hard to distinguish. We used digital photographs of incubating birds taken ~daily at 49 breeding sites during the second half of the incubation period and compared inter-observer variation in distinguishing incubation shifts by each member of the pair. Using this method gave similar results when different subsets of sites were included and the assessment of incubation shifts by three different people produced similar results, yielding a mean shift duration of 6.4 days. Provided pairs with suitable variation in plumage or bill colour are selected, our results demonstrate that a remote camera technique can provide precise data to assess fulmar responses to annual environmental conditions for feeding and breeding.

Female ornamentation in Malurus fairy-wrens: a hidden evolutionary gem for understanding female perspectives on social and sexual selection

Phylogeny, ecological environment, social organisation, and mating system are expected to affect degree of female ornamentation, either directly or indirectly, but our understanding of how female ornaments respond to these forces remains incomplete. This article evaluates the evolutionary history and adaptive significance of three putative ornaments—plumage colouration, bill colouration and tail-length—in female fairy-wrens. Despite considerable research on these traits in male fairy-wrens, they have yet to be studied in any detail in females. Phylogeographic analyses in combination with life-history data suggest that female plumage colouration and bill colouration are under active selection, independent of that experienced by males. Social organisation and mating system, as mediated by ecological environment, may shape degree of ornamentation in these traits among females. In contrast, tail-length appears to be driven directly by natural ecological selection imposed by environmental conditions, leading to parallel trait evolution among the sexes within each species. More refined comparative and population-level investigations of adaptive consequences and proximate mechanisms are future research priorities. The study of female fairy-wrens holds great promise to advance our collective understanding of how the ecological environment interacts with sexual selection and social competition to shape ornament evolution in complex social organisms.

Morphological traits of duck and geese breeds of West Bengal, India

The study pertains to phenotypic characterization of some breeds of duck (common white duck and Indian runner duck), Muscovy ducks (black and white feathered and sepia feathered) besides two breeds of geese (white and brown feathered and white feathered) reared in the state of West Bengal (India). The study was conducted at five locations of the state and comprised 1395 ducks and 600 geese. The data were analysed statistically using mainly descriptive statistics, the differences in mean were analysed using Duncan's multiple range test. Both qualitative and quantitative traits were considered in the study. The qualitative traits were shank colour, bill colour, colour of the feathers, skin colour, egg shell colour, the presence or absence of beans, body carriage, bill type and colour of the eyes, while the quantitative traits included in the study were weight of the ducks and weight of the eggs. Some production traits such as numbers of eggs laid per year and dressing percentage of the drakes and ganders of each breed too have been studied. The ducks and geese are raised under semi-intensive management system and mostly depend on scavenging for their nutritional needs. This results in poor egg production and at times loss of stock because of diseases. The study regarding average egg production indicated that the Muscovy ducks and the geese have poor egg production, whereas the Indian runner followed by the common white duck are potentially the best. The ducks are important source of earnings for the small holder farmers and are raised both for meat and eggs, while the geese are reared mostly for ornamental purpose. However, the populations of the ducks are fast dwindling because of avian influenza in the region and because restocking is mostly being carried out with less adapted Khaki Campbell ducks. This happens mainly because the government farms that were responsible for providing the ducklings for restocking maintain Khaki Campbell ducks and do not have the parental stock of the native duck breeds, while restocking of the Muscovy ducks and geese are carried out by the rearers themselves. There are also no prevailing breeding programmes to conserve, select, maintain and distribute the native breeds of duck and geese. Hence, it is of earnest importance to conserve the avian genetic resources before the population dwindles further.

Toxicity of increasing aflatoxin B1 concentrations from contaminated corn with or without clay adsorbent supplementation in ducklings

A total of 1,280 1-d-old ducks were used in a study to investigate the effects of increasing aflatoxin B1 (AFB1) concentrations from naturally contaminated corn on young ducklings, and the effectiveness of a clay adsorbent (CA) to protect against those effects. Ducks were randomly allotted to 8 treatments (TRT) in a 4 × 2 factorial arrangement with 4 levels of AFB1 (0, 25, 50, and 100 μg/kg) and 2 levels of CA (0 and 0.1%) with 8 pens per TRT and 20 ducks per pen. All ducks were allowed ad libitum access to feed and water during the 21-d experiment. The ADG, ADFI, feed conversion rate, mortality, bill color, and CV of BW of each replicate were measured at the end of the study. Blood and tissue samples from 8 ducks per TRT were obtained on d 21 of the experiment to determine the serum immunoglobulin and protein concentrations, relative organ weights, and intestinal morphology. Average daily gain and relative weights of the liver, spleen, thymus, and bursa of Fabricius decreased linearly (P < 0.05) as dietary AFB1 increased. Serum proteins and intestinal villi heights and villus/crypt ratio followed the same pattern. Bill decolorization ratio, CV of BW, and mortality increased linearly (P < 0.05) as dietary AFB1 increased. Adding 0.1% CA to the diet improved (P < 0.05) the relative weights of the small intestine, spleen, and thymus, and the villus height and villus/crypt ratio of the duodenum and jejunum, as well as the serum IgG and IgM concentrations. Adding CA also reduced (P < 0.05) bill decolorization ratio, CV of BW, mortality, and serum IgA concentration. Therefore, duck performance was negatively affected by increasing AFB1 concentrations in diets. But the addition of 0.1% CA can protect against the detrimental effects caused by AFB1-contaminated corn in diets for ducks.

Effects of Prenatal Testosterone Exposure on Antioxidant Status and Bill Color in Adult Zebra Finches

Permanent offspring modification through maternal hormone transfer is thought to be a tool for mothers to influence life-history trajectories of individual offspring. In birds, yolk hormones influence numerous aspects of the offspring's physiology, including antioxidant status, an important physiological measure that is linked to growth, reproductive effort, and survival. While it is evident that yolk hormones can affect antioxidant status of nestlings, it is not known whether their effect extends beyond the nestling stage. In this study, we use the zebra finch (Taeniopygia guttata) to test experimentally whether exposure to elevated yolk testosterone (T) levels can result in long-term effects on antioxidant status and traits likely to be associated with this measure. Our data show a significant but sex-specific effect with respect to a period from fledging to the age of 7 mo; T males had higher antioxidant status than control males, whereas antioxidant levels did not differ among females and were intermediate compared with the two male groups. Bill color, a trait associated with carotenoids (a specific group of antioxidants) and known to be under the control of circulating levels of T, was not affected by our yolk T manipulation. Bill color (alone or in covariation with egg treatment or sex) did not predict immune responsiveness or antioxidant status. Moreover, there was only weak evidence that antioxidant status predicted the strength of different immune responses. Antioxidant status (in covariation with egg treatment and sex) predicted levels of circulating total antibody levels but did not predict the strength of cell-mediated and humoral immune responses. Our results suggest that yolk T affects antioxidant status independently of these other traits.

Colour also matters for nocturnal birds: owlet bill coloration advertises quality and influences parental feeding behaviour in little owls

Chromatic signals of offspring quality have been shown to play a role in parent-offspring communication in diurnal birds, but are assumed to be useless in dim light conditions because colour-based discrimination probably requires more light. A major ecological and evolutionary conundrum in this scenario is why the nestlings of some nocturnal owls display colourful beaks. Here, we test the hypothesis that yellow bill coloration of owlets of the nocturnal little owl Athene noctua may function as a chromatic signal revealing to parents aspects of quality of their offspring. In a first step, we examined physical variation in bill coloration and its covariation with owlet quality. Secondly, we studied parental provisioning in relation to an experimental manipulation of bill coloration of owlets. Bills of owlets showed higher within-nest variation in yellow-red chroma than in brightness. Plasma carotenoid concentration and nestling immunological status were not associated with chromatic or achromatic features of the bill. Interestingly, however, heavier owlets displayed more yellow bills than lighter ones. The effect of bill coloration on parental favouritism changed with brood size. Parents holding large broods preferentially fed owlets with enhanced over reduced yellow bill coloration, whereas those with small broods did not significantly bias feeding in relation to owlet bill coloration. Our results, based on integration of objective spectrophotometric assessment of colour and experimental procedures, confirm that parent little owls use bill coloration to reveal information on owlet body mass to adjust their feeding strategies, thus highlighting the importance of considering potential chromatic signals for a full comprehension of parent-offspring communication processes in nocturnal bird species.

Correlations of Condition, Testosterone, and Age with Multiple Ornaments in Male House Sparrows: Patterns and Implications

Abstract. Why many animals display several different kinds of ornaments has been of recent interest in animal-communication research. Three key hypotheses have been suggested: multiple ornaments can function as (1) multiple messages (each ornament provides different information), (2) redundant messages or back-up signals (all ornaments provide the same information), and (3) unreliable signals (no information). Here we tested the signal properties of ornamental traits of male House Sparrows (Passer domesticus) to better resolve the potential information different ornaments reveal. We repeatedly measured badge size, wingbar area and color, bill color, and leg color in 170 captive males over 3 years. We found that (1) badge size and wingbar area were related to condition (to mass, tarsus length, and the interaction of both), (2) badge size, wingbar area, and bill color were related to testosterone levels, (3) all ornaments except bill color were related to age, and (4) origin had only minor effects. We concl...

Ornamental bill color rapidly signals changing condition

Ornamental bill color is postulated to function as a condition‐dependent signal of individual quality in a variety of taxonomically distant bird families. Most red, orange, and yellow bill colors are derived from carotenoid pigments, and carotenoid deposition in ornamentation may trade off with their use as immunostimulants and antioxidants or with other physiological functions. Several studies have found that bill color changes in response to physiological perturbations, but how quickly such changes can occur remains unclear. We tested the hypothesis that carotenoid‐based orange bill color of American goldfinches Spinus tristis responds dynamically to rapid changes in physiological stress and reflects short‐term changes in condition. We captured male and female goldfinches and measured bill color in the field and again under captive conditions several hours later. The following day, the captive birds were injected with either immunostimulatory lipopolysaccharide (LPS) or a control saline and changes in bill color were measured over a five day period. Yellow saturation of the bill decreased within 6.5 h between the field and captivity measures on the first day, presumably in response to capture stress. Over the longer experimental period, bill hue and luminance decreased significantly, whereas saturation significantly increased in both LPS and control groups. Bill hue and luminance decreased significantly more in birds treated with LPS than in control birds. Among LPS treated birds, individuals expressing high bill color at the beginning of the experiment lost more color than ‘low‐color’ birds, but still retained higher color at the end of the experiment, suggesting that birds that invest heavily in bill coloration are able to sustain high costs in the face of a challenge. Bill color change may have resulted from rapid reallocation of carotenoids from ornamentation to immune function. However, the complex shifts in bill color over time suggest that bill color may be influenced by multiple carotenoid compounds and/or changes in blood flow or chemistry in vessels just beneath the translucent keratinized outer layer of the bill. We conclude that bill color is a dynamic, condition‐dependent trait that strategically and reliably signals short‐term fluctuations in physiological condition.