Bill Color Research Articles

Spread of yellow-bill-color alleles favored by selection in the long-tailed finch hybrid system

Carotenoid pigments produce the yellow and red colors of birds and other vertebrates. Despite their importance in social signaling and sexual selection, our understanding of how carotenoid ornamentation evolves in nature remains limited. Here, we examine the long-tailed finch Poephila acuticauda, an Australian songbird with a yellow-billed western subspecies acuticauda and a red-billed eastern subspecies hecki, which hybridize where their ranges overlap. We found that yellow bills can be explained by the loss of C(4)-oxidation, thus preventing yellow dietary carotenoids from being converted to red. Combining linked-read genomic sequencing and reflectance spectrophotometry measurements of bill color collected from wild-sampled finches and laboratory crosses, we identify four loci that together explain 53% of variance in this trait. The two loci of largest effect contain the genes CYP2J19, an essential enzyme for producing red carotenoids, and TTC39B, an enhancer of carotenoid metabolism. A paucity of protein-coding changes and an enrichment of associated upstream variants suggest that the loss of C(4)-oxidation results from cis-regulatory evolution. Evolutionary genealogy reconstruction indicates that the red-billed phenotype is ancestral and that yellow alleles at CYP2J19 and TTC39B first arose and fixed in acuticauda approximately 100 kya. Yellow alleles subsequently introgressed into hecki less than 5 kya. Across all color loci, acuticauda-derived variants show evidence of selective sweeps, implying that yellow bill coloration has been favored by natural selection. Our study illustrates how evolutionary transitions between yellow and red coloration can be achieved by successive selective events acting on regulatory changes at a few interacting genes.

Genomic islands of speciation harbor genes underlying coloration differences in a pair of Neotropical seedeaters.

Incomplete speciation can be leveraged to associate phenotypes with genotypes, thus providing insights into the traits relevant to the reproductive isolation of diverging taxa. We investigate the genetic underpinnings of the phenotypic differences between Sporophila plumbea and Sporophila beltoni. Sporophila beltoni has only recently been described based, most notably, based on differences in bill coloration (yellow vs. black in S. plumbea). Both species are indistinguishable through mtDNA or reduced-representation genomic data, and even whole-genome sequencing revealed low genetic differentiation. Demographic reconstructions attribute this genetic homogeneity to gene flow, despite divergence in the order of millions of generations. We found a narrow hybrid zone in southern Brazil where genetically, yet not phenotypically, admixed individuals appear to be prevalent. Despite the overall low genetic differentiation, we identified 3 narrow peaks along the genome with highly differentiated SNPs. These regions harbor 6 genes, one of which is involved in pigmentation (EDN3) and is a candidate for controlling bill color. Within the outlier peaks, we found signatures of resistance to gene flow, as expected for islands of speciation. Our study shows how genes related to coloration traits are likely involved in generating prezygotic isolation and establishing species boundaries early in speciation.

APPLICATION OF MULTIVARIATE STATISTICAL ANALYSIS IN CHARACTERISING THE PHENOTYPIC VARIABILITY OF LOCALLY ADAPTED MUSCOVY DUCKS (CAIRINA MOSCHATA) IN NIGERIA

While there are studies that describe the biometric traits and phenotypic variations in Muscovy ducks in Nigeria, there are limited studies that employ a multivariate approach to depict the phenotypic variability of Muscovy ducks in Nigeria. Therefore, this study aimed to explicate genetic variabilities within C. moschata using qualitative and biometric traits. This study used a multivariate statistical method to phenotypically characterise locally adapted Muscovy duck populations from seven ecogeographical locations in Ibadan, Nigeria. Four qualitative traits (eye colour, bill colour, bean colour and shank colour) and eleven biometric traits (head length, neck length, body length, wings length, shank length, toe length, thigh length, bill length, breast length, breast width and bodyweight) were evaluated in 201 ducks (109 males and 92 females). To study the possible effects of geographical locations on selected phenotypes, frequency distribution, univariate analysis, stepwise and canonical discriminant analyses and cluster analysis were performed. The association between body weight (BWT) and other biometric traits was assessed using the Pearson product-moment correlation coefficient. Male ducks (drakes) were generally more abundant than female ducks (hens). The most prevalent colour traits of locally adapted Muscovy ducks were brown eye colour (70.65 %), black bean colour (62.69 %), pinkish white bill colour (45.27 %) and grey shank colour (56.22 %). Overall, ecogeographical location did not significantly affect (p < 0.05) the measured biometric traits. However, across all locations, the sexual dimorphism was favourable in male ducks, with respect to biometric traits. Stepwise-canonical discriminant analysis revealed a substantial intermixing of biometric traits, especially in Molete, Oje, Adogba and Ajibode ducks. Similarly, the cluster analysis, although it separated the birds into different clusters, showed some level of admixture. The small Mahalanobis distance (0.61 − 3.88) suggested that, with respect to location, there was more morphological similarity than dissimilarity between ducks. The correlation analysis revealed that the body weight of ducks can be fairly estimated from other biometric traits due to their positive, statistically significant correlation. In general, the ducks from all seven ecogeographical locations were rather homogeneous than heterogeneous.

Bill color is dynamic across the breeding season but not condition‐dependent in Atlantic puffins

AbstractSexually monomorphic species have been historically overlooked in the sexual/social selection literature, but there is growing evidence that mutual ornamentation can be driven by selective forces such as mutual sexual selection or selection for individual recognition. Examining the properties of a trait may elucidate which forces most likely play a role, especially when comparing the characteristics of quality and identity traits. Atlantic puffins (Fratercula arctica) are an example of a mutually ornamented monomorphic species, where both males and females display a bright orange‐red bill and orange gape rosette during the breeding season and are ornamented to similar degrees. In this study, we investigate whether the properties of the colorful bill and rosette, specifically lability across the breeding season and condition‐dependence, more closely align with signals of quality or identity. Our findings support prior work that the bill is sexually monochromatic from an avian visual perspective. We also determined that the bill changes in a discriminable way within individuals across the breeding season and is especially dynamic in the fleshy rosette. However, no metric of color on any region of the bill or rosette was significantly related to current body condition. Ultimately, we argue that bill color could potentially function as a quality signal, although further study is needed to determine which aspect of quality coloration signals, if not condition. These results provide a basis for experimentally evaluating the signal value of the colorful bill in Atlantic puffins (e.g., color manipulation experiments), and more broadly, a framework for investigating the properties of mutual ornamentation in avian species.

The impact of diet on sperm length in the long‐tailed finch (Poephila acuticauda)

Sperm traits are important in determining fertilisation success and are metabolically expensive to produce. There is little known about how energy acquisition and allocation affect sperm traits in avian taxa. This study assesses the impact of experimentally manipulated diet on long‐tailed finch sperm by comparing the length of sperm components (head, midpiece, flagellum and total sperm) between the treatment groups (homogenous diet and diverse diet) and across time points (before and after the experiment). Diet homogeneity was manipulated as this may impact diet quality in a species that is usually fed a diversity of seed species to thrive in captivity. Our results showed no impact of diet on the length of different sperm components. These results contrast with findings of a similar recent study of the zebra finch which found a significant level of diet‐affected plasticity in midpiece length. For both diet treatment groups in this study there was a slight but significant increase in head, flagellum and total sperm length over the treatment period. Despite this, all sperm components were highly repeatable, consistent with the finding from observational studies in passerine birds. The efficacy of our dietary manipulation was confirmed by a significant reduction in the saturation of bill colour in the long‐tailed finches as a result of the homogenous diet, and a difference in body mass across the treatment groups.

Experimentally testing mate preference in an avian system with unidirectional bill color introgression.

Mating behavior can play a key role in speciation by inhibiting or facilitating gene flow between closely related taxa. Hybrid zones facilitate a direct examination of mating behavior and the traits involved in establishing species barriers. The long-tailed finch (Poephila acuticauda) has two hybridizing subspecies that differ in bill color (red and yellow), and the yellow bill phenotype appears to have introgressed ~350 km eastward following secondary contact. To examine the role of mate choice on bill color introgression, we performed behavioral assays using natural and manipulated bill colors. We found an assortative female mating preference for males of their own subspecies when bill color was not manipulated. However, we did not find this assortative preference in trials based on artificially manipulated bill color. This could suggest that assortative preference is not fixed entirely on bill color and instead may be based on a different trait (e.g., song) or a combination of traits, or alternatively may be due to lower statistical power alongside the bill manipulations being unconvincing to the female choosers. Intriguingly, we find a bias in the inheritance of bill color in captive bred F1 hybrid females. Previous modeling suggests that assortative mate preference and this kind of partial dominance in the underlying genes may together contribute to introgression, making the genetic architecture of bill color in this system a priority for future research.

Effects of anthropogenic noise on cognition, bill color, and growth in the zebra finch (Taeniopygia guttata)

Effects of anthropogenic noise on cognition, bill color, and growth in the zebra finch (Taeniopygia guttata)

Oestradiol reduces female bill colour in a mutually ornamented bird.

Carotenoid-based colour signals can be costly to produce and maintain, and trade-offs between signalling and other fitness traits are expected. In mutually ornamented species, trade-offs with reproduction may be stronger for females than males, because females often dedicate more resources to offspring production, which may lead to plastic investment in colour signals and plastic sexual dichromatism. Oestradiol is a candidate mediator of this trade-off because it regulates reproductive physiology and may also influence the expression of coloration. We tested this hypothesis by giving female common waxbills (Estrilda astrild) either oestradiol (17β-oestradiol) or empty implants during the early breeding season and measured spectral reflectance of carotenoid-based bill coloration weekly for two months. Using a model of avian vision, we found that bill colour in oestradiol-implanted females became less saturated, less red in hue and brighter, compared with control females and with unimplanted males. This resulted in a change in bill sexual dichromatism from imperceptible to perceptible. Results support the hypothesis that female reproductive physiology influences investment in coloration through changes in oestradiol and show a form of female-driven plastic sexual dichromatism. Greater sensitivity of female colour to physiological and/or environmental conditions helps explain why differences in sexual dichromatism among species differing in ecology often evolve owing to changes in female rather than male phenotype.

Effects of dietary paddy rice on growth performance, carcass traits, bare skin color, and nutrient digestibility in geese

The aim of this study was to investigate the effects of dietary paddy rice on growth performance, carcass traits, bare skin color, and nutrient digestibility in geese. A total of 300 twenty-eight-day-old male goslings were randomly divided into 5 treatment groups with 6 pens containing 10 goslings each. The geese were raised for 42 d on feed with 0% (control), 13, 26, 39, or 52% dietary paddy rice inclusion. Body weight and feed intake per pen were recorded from the arrival of goslings to the end of the trial. On d 70, two goslings were selected from each pen, one of which was used to measure slaughter performance, meat quality, meat proximate composition, and bare skin color, and one was used to determine nutrient utilization. The results showed that goslings fed a diet containing 26, 39, and 52% paddy rice had a higher final body weight, average daily feed intake, and average daily gain than those in the control group (P < 0.05). The abdominal fat yield in dietary paddy rice groups was higher than that of the control group (P < 0.05). There were no effects on the moisture, protein, and fat contents of breast and thigh muscle among the five treatments (P > 0.05). Compared to the control group, the breast muscle of geese fed the paddy rice had a lower L* value and a higher a* value (P < 0.05). Dietary paddy rice decreased the bill score of geese (P < 0.05). Geese in the paddy rice groups exhibited higher total starch digestibility than geese in the control group (P < 0.05). The digestibility of energy, crude protein, crude fat, crude fiber, NDF, and ADF did not differ between groups (P > 0.05). In conclusion, paddy rice is an excellent energy source in geese diets and could improve the growth performance, breast muscle color, and utilization of total starch but increase the abdominal fat yield and decrease the bill color of geese.

Characterization of duck germplasm of eastern hill and plateau region of Jharkhand

Information about phenotypic characteristics is a basic need in animal genetic resource conservation and improvement. Phenotypic characteristics of Jharkhand ducks from six districts (Palamu, Gadhwa, Latehar, Lohardaga, Khuti, and Simdega) were studied. Data on morphological and morphometric traits were analyzed. The results revealed that the predominant plumage colours of the head, neck, breast, wings and tails were black (56.25%) in drake, and black and white mix (65.33%) in duck; white and black/brown mix (62.50%) in drake, and white (79.33%) in duck; brown (41.25%) in drake, and white and black/brown mix (52.67%) in duck; black/brown and white mix (43.75%) in drake and duck (74.67%); black in drake (75%) and duck (90%) respectively. The dominant bill colour in drake was greenish black (56.25%) followed by orange (25%) and duck bill colour was black (58.67%) followed by orange (22%), whereas dominant eye colour was brown in both the sexes. The predominant shank and web colour were orange (65.0%) in drake and duck (68.0%) respectively. The Jharkhand ducks are unique in their morphological features with attractive black and white plumage colour pattern. The ducks are well acclimatised to local agro-climatic conditions with less input from duck farmers. The hatching and brooding process are natural. The average egg production was 66.92±2.00 eggs. The average adult body weights of drake and ducks were 1.64±23.19 and 1.51±30.09 kg, respectively. Variations were observed in qualitative traits. The observed phenotypic diversity in Jharkhand local ducks could be useful in designing breeding programs and selection.

Testosterone, signal coloration, and signal color perception in male zebra finch contests.

Many animals use assessment signals to resolve contests over limited resources while minimizing the costs of those contests. The carotenoid-based orange to red bills of male zebra finches (Taeniopygia guttata) are thought to function as assessment signals in male-male contests, but behavioral analyses relating contest behaviors and outcomes to bill coloration have yielded mixed results. We examined the relationship between bill color and contests while incorporating measurements of color perception and testosterone (T) production, for an integrative view of aggressive signal behavior, production, and perception. We assayed the T production capabilities of 12 males in response to a gonadotropin-releasing hormone (GnRH) challenge. We then quantified the initiation, escalation, and outcome of over 400 contests in the group, and measured bill color using calibrated photography. Finally, because signal perception can influence signal function, we tested how males perceive variation in bill coloration, asking if males exhibit categorical perception of bill color, as has been shown recently in female zebra finches. The data suggest that males with greater T production capabilities than their rivals were more likely to initiate contests against those rivals, while males with redder bills than their rivals were more likely to win contests. Males exhibited categorical color perception, but individual variation in the effect of categorical perception on color discrimination abilities did not predict any aspects of contest behavior or outcomes. Our results are consistent with the hypotheses that T plays a role in zebra finch contests and that bill coloration functions as an aggressive signal. We suggest future approaches, based on animal contest theory, for how links among signals, perception, and assessment can be tested.

PREFORMATIVE MOLT EXTENT AND AGING AND SEXING CRITERIA FOR EIGHT HUMMINGBIRD SPECIES IN SOUTHEASTERN PERU

Little attention has been paid to molt and age criteria in hummingbirds despite the importance of molt and age to numerous behavioral and ecological questions. We examined age-based molt patterns and bill corrugations in eight species of lowland Amazonian hummingbirds. Molt strategies and rates of bill smoothing were similar to those of more well-studied North American species, with all species showing partial preformative molts (replacing only body feathers and some wing coverts and retaining all remiges and rectrices), and bill corrugations reducing to less than 10% of bill length in all species during the first annual cycle. Several species showed evidence of delayed maturation in males in regard to plumage characteristics or bill coloration.

Ecological effects on female bill colour explain plastic sexual dichromatism in a mutually-ornamented bird

Sex differences in ornamentation are common and, in species with conventional sex roles, are generally thought of as stable, due to stronger sexual selection on males. Yet, especially in gregarious species, ornaments can also have non-sexual social functions, raising the possibility that observed sex differences in ornamentation are plastic. For example, females may invest in costly ornamentation more plastically, to protect body and reproductive ability in more adverse ecological conditions. We tested this hypothesis with experimental work on the mutually-ornamented common waxbill (Estrilda astrild), supplementing their diets either with pigmentary (lutein, a carotenoid) or non-pigmentary (vitamin E) antioxidants, or alleviating winter cold temperature. We found that both lutein and vitamin E supplementation increased red bill colour saturation in females, reaching the same mean saturation as males, which supports the hypothesis that female bill colour is more sensitive to environmental or physiological conditions. The effect of vitamin E, a non-pigment antioxidant, suggests that carotenoids were released from their antioxidant functions. Alleviating winter cold did not increase bill colour saturation in either sex, but increased the stability of female bill colour over time, suggesting that female investment in bill colour is sensitive to cold-mediated stress. Together, results show that waxbill bill sexual dichromatism is not stable. Instead, sexual dichromatism can be modulated, and even disappear completely, due to ecology-mediated plastic adjustments in female bill colour.

Evaluating evidence of mitonuclear incompatibilities with the sex chromosomes in an avian hybrid zone.

The exploration of hybrid zones and the intergenomic conflicts exposed through hybridization provide windows into the processes of divergence and speciation. Sex chromosomes and mitonuclear incompatibilities have strong associations with the genetics of hybrid dysfunction. In ZW sex-determining systems, maternal co-inheritance of the mitochondrial and W chromosomes immediately exposes incompatibilities between these maternal contributions of one species and the Z chromosome of another. We analyze mitochondrial and Z chromosome admixture in the long-tailed finch (Poephila acuticauda) of Australia, where hybridizing subspecies differ prominently in Z chromosome genotype and in bill color, yet the respective centers of geographic admixture for these two traits are offset by 350 km. We report two well-defined mitochondrial clades that diverged ∼0.5 million years ago. Mitochondrial contact is geographically co-located within a hybrid zone of Z chromosome admixture and is displaced from bill color admixture by nearly 400 km. Consistent with Haldane's rule expectations, hybrid zone females are significantly less likely than males to carry an admixed Z chromosome or have mismatched Z-mitochondrial genotypes. Furthermore, there are significantly fewer than expected mitonuclear mismatches in hybrid zone females and paternal backcross males. Results suggest a potential for mitonuclear/sex chromosome incompatibilities in the emergence of reproductive isolation in this system.

Urban environment alter the timing of progression of testicular recrudescence in tree sparrow (Passer montanus).

Urbanization is a rapidly growing phenomenon that affects wildlife. Laboratory studies show the effects of night light on the physiology of the organisms. Limited studies have been conducted on birds in their natural habitat. Here, we studied the effects of the urban environment on reproduction-linked phenomenon and molecules involved in the regulation of seasonal breeding. Birds (N=5/time/site) were procured from urban and rural sites at specific times, i.e., in March (stimulatory phase), June (reproductive phase), September (refractory phase), and December (sensitive phase) of 2018. Immediately after procurement, birds were brought to the laboratory. Bodyweight, bill color, molt in body feathers, and testes size were recorded. The next day, all the birds were sacrificed in the middle of the day. Blood was collected and serum was used for ELISA of corticosterone, triiodothyronine (T3), and thyroxine (T4). mRNA levels of thyroid-stimulating hormone-β (Tshβ), type 2 deiodinase (Dio2), type 3 deiodinase (Dio3), gonadotropin-releasing hormone (GnRh), and gonadotropin inhibitory hormone (GnIh) were measured in hypothalamic tissue. Urban birds showed higher levels of corticosterone during the stimulatory phase. There was a delay in the initiation of testicular growth in urban birds and it was supported by reduced levels of T3 in blood plasma and relatively lower transcription of Dio2 and GnRH mRNA in urban birds. Our findings suggest that the urban environment delays the timing of reproduction in birds and could be the consequence of local environmental conditions.

Qualitative and quantitative characteristics of Andaman local duck

Qualitative and quantitative traits are useful descriptors of any breeds under inhabited agro-ecological conditions. Hence, the present study was undertaken to characterize the local duck populations in Andaman based on morphology and morphometric observations under field conditions. Morphology for Drake and Ducks was noted by visual observation. Body measurements (cm) were recorded on length and width of bill and head, length of body, neck, and shank, wingspan, and body circumference. The overall mean values were (cm); 4.01±0.07 (bill length), 1.54±0.04 (bill width), 8.42±0.20 (head length), 3.70±0.36 (head width), 20.32±0.95 (neck length), 48.52±0.58 (body length), 82.27±0.50 (wingspan), 37.75±0.93 (body circumference) and 3.37±0.06 (shank length). Drakes of Andaman local ducks were having more values than ducks. The common bill colour was yellow with black tip, shank and web were yellow, and skin was mostly black. The plumage colour patterns were gray, black, and chocolate in different parts of the body. A white band on the neck was commonly found. The present study generates the baseline information which may be useful for formulation of systematic breeding policy to exploit potentiality of these local ducks and their conservation.

High temperature attenuates testicular responses in tree sparrow (Passer montanus)

The majority of birds use environmental cues to time their reproduction. Photoperiod is the most dominant cue, but other environmental factors may play a critical role in successful reproduction. Some previous studies show the effect of temperature on the timing of nest building and reproduction. Here we tested if the temperature can modulate the reproductive responses of tree sparrows. Three experiments were performed on adult male birds. In experiment 1, birds (n = 5/group) were exposed to either high (30 ± 2 °C) or low temperature (20 ± 2 °C). Change in body mass, bill color, and testes volume was recorded every 30 days. In experiment 2, a similar temperature protocol was followed, but birds were euthanized after 30 days. In experiment 3, birds were first exposed to SD (8L:16D) for 30 days but either with high (30 ± 2 °C) or low temperature (20 ± 2 °C). After 30 days, birds were exposed to LD (14L:10D), but half of the high-temperature birds were moved to low temperature, and half of the low-temperature birds were moved to high temperature. After 30 days, all birds were euthanized. In experiment 2 and 3 immediately after euthanization birds, blood samples were collected, serum was used for hormone assay. mRNA levels of thyroid-stimulating hormone-β (Tshβ), type 2 deiodinase (Dio2), type 3 deiodinase (Dio3), gonadotropin-releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) were measured in hypothalamic tissue. Results from experiment 1 show that high temperature attenuates the testicular responses and accelerates the timing of regression. Experiment 2 shows that on day 30, testicular responses are similar, but reproductive genes express differentially in two groups. Experiment 3 shows that exposure to high temperatures during the photosensitive stage affects the testicular response at the poststimulatory state. Together, these findings suggest that high temperature modulates reproductive responses of tree sparrow.

Characterization of Maithili duck in middle Gangetic plain of Bihar

A study was conducted in middle Gangetic plain of Bihar to evaluate the smallholder duck production systems in the regions. A total of 70 duck farmers in Bihar were selected for this study. The information were collected by using standard questionnaire and an interview. The majority of the farmers (60%) belonged to middle-aged category. Majority of duck rearers in Bihar rears the duck more than 20 years. The average flock size was 6.1±0.33. Ducks were raised under semi-intensive management system and mostly depend on scavenging for their nutritional needs in the study area. About 88.6% farmers provided some kind of housing for their ducks, usually constructed mainly from simple and locally available materials in their backyard. Farmers did not possess any permanent shelter. Majority of the farmers (94.29%) did not vaccinate against the diseases of ducks due to unavailability. In both drake and duck, body carriage was slightly upright and Bill shape was horizontal. The ducks are raised both for meat and eggs. The average annual egg production per duck was ranged to be 30–60 eggs per annum. The average body weight of drake and duck were 1.40±0.07 and 1.37±0.08 kg, respectively. The predominant plumage colours of the Head, neck, breast, wing, and tail were brown (43.75%), brown and white mix with or without white ring (53.75%), brown (80.00%), brown, black and white mix (57.50%) and brown (40.00%) respectively. The dominant bill colour were yellow (43.75%) and web colour were orange (56.25%) respectively in Maithili duck. Mosaic plumage colour pattern was predominant in Maithili duck of Middle gangetic plain.

Sexually selected traits as bioindicators: exposure to mercury affects carotenoid-based male bill color in zebra finches.

To examine whether sexually selected traits are particularly sensitive bioindicators of environmental toxicants, we assessed the effects of exposure to environmentally relevant dietary concentrations of the pollutant methylmercury on pigment coloration in zebra finches (Taeniopygia guttata). First, we tested whether effects of methylmercury on coloration were influenced by timing of exposure. Birds were either exposed developmentally (up to 114 days after hatching), as adults (after reaching sexual maturity), or for their entire life. Bill coloration, which is a carotenoid-based, sexually selected trait, was less red in males with lifetime exposure to methylmercury, compared to controls. Neither adult, nor developmental exposure influenced bill color in adult males, with the possible exception of early exposure of nestlings. Among females, where bill color is not under strong sexual selection, neither lifetime nor adult exposure to methylmercury affected bill color. For males and females, there was no effect of either lifetime or adult methylmercury exposure on coloration of back feathers, which is a non-sexually-dimorphic, melanin-based trait that is not likely the result of sexual selection. This study is a comprehensive experimental test of the proposal that sexually selected traits may be particularly useful bioindicators of the stress imposed by environmental toxins such as methylmercury.

Carbon δ13C Isotopic Marker Values Correlate with Carotenoid-Based Bill Colouration in Adult Yellow-Legged Gulls Larus michahellis

La coloracion basada en carotenoides que presentan muchas aves puede reflejar honestamente la calidad del individuo, ya que deben ser obtenidos mediante la dieta. Estos pigmentos son importantes para varias funciones fisiologicas y los individuos pueden buscar compensar entre la distribucion de los carotenoides para estos usos y su acumulacion para atributos sexuales secundarios y sociales. La gaviota patiamarilla Larus michahellis es una especie oportunista que se alimenta de una gran variedad de presas. En este trabajo hemos estudiado si la coloracion basada en carotenoides (pico, mancha roja, anillo orbital) esta relacionada con la ecologia trofica inferida a partir de la composicion isotopica de plumas de aves adultas en tres colonias de esta especie. El marcador isotopico del δ13C correlaciono negativamente con la coloracion basada en carotenoides (area de la mancha roja). Contrariamente a la prediccion hecha a priori, el marcador indica que un mayor consumo de presas terrestres y recursos de vertedero podria ayudar a generar una mancha roja del pico mayor en gaviotas de cualquier sexo. En hembras, no se detecto ninguna correlacion entre las signaturas isotopicas y el volumen de los huevos. El resultado de que un consumo mayor de presas marinas implica una mancha roja menor apoya otros descritos en estudios anteriores que muestran efectos aparentemente positivos de comer en ambientes terrestres humanos sobre el fenotipo de aves adultas. Los resultados pueden sugerir que un mayor consumo de presas marinas puede no ser tan positivo como el presentado en estudios previos. Sin embargo, el efecto de los componentes toxicos potenciales que se pueden obtener de algunas fuentes de alimentacion deberia ser estudiado mas a fondo. Deberiamos de considerar tambien los probables efectos subletales retardados asociados a estos habitats y que se ejercerian sobre los adultos y, probablemente tambien, sobre los pollos.