Breast Feathers Research Articles

Breast Feathers as an Air-current Sense Organ for the Control of Flight Behaviour in a Songbird (Carduelis spinus)

Analysis of the flight behaviour of siskins (Carduelis spinus) was made possible by tethering them with a harness to a flight balance in a wind tunnel. It could be shown that the breast feathers work as an air-current sense organ influencing the siskins' flight pattern and the aerodynamic parameters.

Talking Turkey: Teaching about North America's Greatest Conservation Story with Children with Visual Impairments

Gobble Gobble! was heard in the hallways of a middle school in the southeastern United States, and the sound was made by a group of students who all had visual impairments. The students were learning about the comeback of the wild turkey in North America, one of the most successful conservation stories in this country. Using a curriculum provided by the National Wild Turkey Federation (NWTF), the students were writing, acting, cooking, conducting interviews, and using tactile exploration in an effort to learn about the physical features and habitat of wild turkeys, along with research conducted on these animals. The lessons in the curriculum are aligned with the standards of the National Science Education. These standards include Scientific Inquiry Content Standard A, Life Science Content Standard C, Science and Technology Science Content Standard E, Science in Personal and Social Perspectives Content Standard F, and History and Nature of Science Content Standard G (National Research Council, 1996). Students who are visually impaired are often taught science concepts with curricula that depend on visual observations, which may present barriers to the students' participation in lessons. Many manuals explain how to teach students with visual impairments in the area of science (Dion, Hoffman & Matter, 2000; Hadary & Cohen, 1978; Koenig & Holbrook, 2000; Kumar, Ramassamy, & Stefanich, 2001; Willoughy & Duffy, 1989). However, little research has been conducted to determine the effectiveness of these curricular materials. CURRICULUM As described earlier, the curriculum of NWTF was used for this study. The curriculum was developed by practitioners and experts to help students gain an appreciation of the resurgence of the wild turkey in North America and the impact the conservation efforts of NWTF have had on the environment. It had never been used with students who are visually impaired, however, and thus the curriculum had to be modified to be accessible for these students. Instead of viewing pictures of turkeys and other animals in the turkey's habitat, for example, the students were able to explore taxidermy models of a wild turkey and the skulls, pelts, and feathers of other animals. Instead of pictures of turkey calls, the students were given the opportunity to meet with a champion turkey caller and explore his equipment. All written materials were reproduced in the students' preferred media. In addition, attention to the expanded core curriculum was given. The students made cookies in the shape of turkeys, wrote thank-you notes to all the speakers, practiced orientation and mobility skills on a field trip, and met with state wildlife conservationists to explore careers in conservation. METHODOLOGY Instructional intervention The teacher brought a taxidermy model of a stuffed female wild turkey into the classroom. She guided the hands of students over the various parts of the bird to help them understand the size and parts of the turkey, stopping at various spots on the bird to point out the wing feathers, tail feathers, breast feathers, and beard. So the students could understand the sounds of turkeys, the teacher played an audio recording of turkey calls. The students listened carefully to the sounds and wrote their impressions and descriptions of the calls. To reinforce their knowledge, a champion turkey caller visited with the students, and they listened to his calls and learned how to make their own calls. Other examples of lesson plans included learning about the ways turkeys are used in various cultures, writing articles about their experiences for the local newspaper, acting like a wild turkey, learning about conservation careers through a visit by the state turkey biologist, writing poetry about wild turkeys, exploring transportation boxes for wild turkeys, and writing want ads for the habitat of the turkey. At the culmination of the instruction, the students attended NWTF's annual convention. …

Mercury levels in the feathers of breeding seabirds in the Seychelles, western Indian Ocean, from 1996 to 2005

We analysed mercury levels in the breast feathers of several breeding seabirds—White-tailed Tropicbird (Phaethon lepturus), Audubon's Shearwater(Puffinus lherminieri), Lesser Noddy (Anous tenuirostris), White Tern (Gygis alba), Sooty Tern (Onychoprion fuscata) and Roseate Tern (Sterna dougallii)—on Aride Island in the Seychelles during three periods between 1996 and 2005. Mercury concentrations tended to be higher in the second sampling period (2002–03) than the first (1996–97), particularly for inshore-feeding species. El Niño events in 1997–99 and 2002–03 might help to explain this pattern, through an increase in mercury bioavailability for seabirds that forage inshore. However, levels of mercury in tissue decreased significantly from the first period (1996–97) to the third period (2004–05) for inshore-foraging species (Lesser Noddy mean ± s.e.: 0.82 ± 0.02 mg g−1 v. 0.53 ± 0.06 μg g−1 respectively) and more wide-ranging, offshore-feeding species (Sooty Tern: 1.16–0.05 v. 0.59 ± 0.04; White-tailed Tropicbird: 1.82 ± 0.05 v. 1.43 ± 0.09). Wide-ranging species of seabirds are more likely to be useful bioindicators at large spatial scales, with such species suggesting a decreasing trend in mercury pollution in the western Indian Ocean.

Alcid Feathers Wet on one Side Impede Air Outflow Without Compromising Resistance to Water Penetration

Abstract. While diving, small alcids appear wet, suggesting that their feathers repel water poorly. Nevertheless, once wet, their plumage resists water penetration effectively. This study's objective was to evaluate the effect of feather wetting on the critical penetration pressure of air (maximum pressure for resistance to air penetration, Pa) and water (Pw). We measured these values in breast feathers of Xantus's Murrelet (Synthliboramphus hypoleucus) and Cassin's Auklet (Ptychoramphus aleuticus) under two conditions : dry (feathers with separated barbs) and wet on one side (feathers with aggregated barbs). Dry feathers of both alcids did not resist air penetration at any pressure, but feathers wet on one side resisted 1.25 kPa. For Xantus's Murrelet Pw was 1.44 kPa, for Cassin's Auklet 1.36 kPa. These results support the hypothesis that plumages that appear wet could minimize heat loss by reducing the exchange of air within the plumage while the bird is diving.

Experiments on colour ornaments and mate choice in king penguins

Research on animal ornaments used in mate choice has largely focused on males, particularly for bird species with sexually dimorphic coloured patches of feathers and integument. Relatively less information is available for coloured ornaments of sexually monomorphic species and the use of these ornaments during mate choice. The king penguin, Aptenodytes patagonicus, is a monogamous marine bird in which both sexes show very similar coloured ornaments (UV and yellow–orange colours on the beak, yellow–orange auricular feathers, and yellow to rusty-brown breast feathers). These ornaments have previously been implicated in mate choice. We used manipulative experiments to test the role of coloured feather patches in the choice of partners that occurs during pair formation. Experimental reduction of auricular patch size delayed pairing, and alteration of auricular and breast patch colour from yellow to white caused an even stronger delay (white treatments gave adults the appearance of immature birds). Surprisingly, we found that time to pairing did not differ between treatments for females, but males showed significant delays in pairing in general and especially when treated. Thus, females seemed to be more selective in mate choice than males, a phenomenon that might be explained by a male-biased sex ratio in the colony. Nevertheless, our results indicate that choice of mate may be much stronger in one of the sexes in what appears to be a sexually monomorphic species, for which we expected sexual selection to favour mutually strong male and female mate choice.

Extra‐pair fertilizations contribute to selection on secondary male ornamentation in a socially monogamous passerine

Despite considerable research effort, it remains unclear whether extra-pair fertilizations (EPF) drive the evolution of male secondary ornamentation in socially monogamous systems. In this study, we test the hypothesis that EPF contribute to the evolution or maintenance of male feather ornamentation in a sexually dichromatic passerine, the Scarlet Rosefinch, Carpodacus erythrinus. We show that the colouration of ornamental breast feathers is a good predictor of basic sources of variation in male annual reproductive output in rosefinches and that the annual realized reproductive success of males is positively associated with measures of ornamental colouration only when gains and losses because of EPF are considered. The results indicate that EPF in rosefinches may rely on absolute (good genes) rather than self referential (genetic complementarity) criteria of mate choice. Our study corroborates the potentially important role of EPF in the evolution and/or maintenance of elaborate male ornaments in socially monogamous taxa.

UV plumage color is an honest signal of quality in male budgerigars

AbstractElaborate and colorful feathers are important traits in female mate choice in birds. Plumage coloration can result from pigments deposited in feathers such as carotenoids and melanins, or can be caused by nano‐scale reflective tissues (structurally based coloration), usually producing ultraviolet (UV) coloration. Structural colorations remain the least studied of the three most important feather colorations. Previous studies have found a female preference for UV color in the budgerigar, Melopsittacus undulatus, but it is not clear what information this ornament conveys, nor what is the possible cost associated with its production. We investigated possible correlations between immune response and plumage color of wild‐type (green) male budgerigars. In particular we measured the wing web swelling resulting from injection of phytohaemagglutinin (PHA). We did not detect any correlation between the sedimentation rate and morphological and color variables. We found that UV chroma is the best predictor for the cutaneous immune activity. Indeed, male budgerigars with high UV reflectance in the breast feathers showed stronger immune responses. These results are consistent with the idea that UV colors are special signals conveying information about a bird's condition.

Linking isotopic and migratory patterns in a pelagic seabird

The value of stable isotope analysis in tracking animal migrations in marine environments is poorly understood, mainly due to insufficient knowledge of isotopic integration into animal tissues within distinct water masses. We investigated isotopic and moult patterns in Cory's shearwaters to assess the integration of different stable isotopes into feathers in relation to the birds' transoceanic movements. Specimens of Mediterranean Cory's shearwater Calonectris diomedea diomedea caught accidentally by Catalan longliners were collected and the signatures of stable isotopes of C (delta(13)C), N (delta(15)N) and S (delta(34)S) were analysed in 11 wing and two tail feathers from 20 birds, and in some breast feathers. Based on isotopic signatures and moult patterns, the feathers segregated into two groups (breeding and wintering), corresponding to those grown in the Mediterranean or Atlantic regions, respectively. In addition, feathers grown during winter, i.e. moulted in Atlantic waters, were grouped into two isotopically distinct profiles, presumably corresponding to the two main wintering areas previously identified for Mediterranean Cory's shearwater in tracking studies. N signatures mainly indicated the Mediterranean-to-Atlantic migration, whereas C and S signatures differed according to the Atlantic wintering area. Our results indicate that isotopic signatures from distant oceanic regions can integrate the feathers of a given bird and can indicate the region in which each feather was grown. This study thus underscores how stable isotope analysis can link marine animals to specific breeding and wintering areas, and thereby shed new light on studies involving assignment, migratory connectivity and carry-over effects in the marine environment.

Origin-related differences in plumage coloration within an island population of great tits (Parus major)

Several studies have described geographic variation in plumage coloration, providing important insights into the processes of local adaptation and speciation. Given that such variation appears to be common, individuals of different origin within a single population may vary accordingly. However, as yet no study has been able to test for such origin-related differences. The population of great tits ( Parus major L., 1758) on the small Dutch island of Vlieland is especially suitable for such a study, as we know of every breeding adult whether it has been born on the island or not, and if it is, where on the island it was born. Furthermore, we have previously found large differences in clutch size and survival among birds of different origin in the same population. Here, we measured the spectral reflectance of the yellow breast feathers, and found that yearling, but not older, birds born in the eastern part of the island had feathers that were of a less bright yellow and UV than birds born elsewhere, irrespective of where they were breeding. Interestingly, this difference in coloration among yearlings of different origin shows a remarkable similarity with the genetic differences found earlier in this population with respect to clutch size and local survival. We thus show that systematic differences in color signals may exist within populations, among individuals of different origin, and we argue that it is crucial that such variation and its potential implications be accounted for irrespective of whether these differences have a genetic or an environmental basis.

Mercury correlations among six tissues for four waterbird species breeding in San Francisco Bay, California, USA

Despite a large body of research concerning mercury (Hg) in birds, no single tissue has been used consistently to assess Hg exposure, and this has hampered comparisons across studies. We evaluated the relationships of Hg concentrations among tissues in four species of waterbirds (American avocets [Recurvirostra americana], black-necked stilts [Himantopus mexicanus], Caspian terns [Hydroprogne caspia; formerly Sterna caspia], and Forster's terns [Sterna forsteri]) and across three life stages (prebreeding adults, breeding adults, and chicks) in San Francisco Bay, California, USA. Across species and life stages, Hg concentrations (least square mean +/- standard error) were highest in head feathers (6.45 +/- 0.31 microg/g dry wt) and breast feathers (5.76 +/- 0.28 microg/g dry wt), followed by kidney (4.54 +/- 0.22 microg/g dry wt), liver (4.43 +/- 0.21 microg/g dry wt), blood (3.10 +/- 0.15 microg/g dry wt), and muscle (1.67 +/- 0.08 microg/g dry wt). Relative Hg distribution among tissues, however, differed by species and life stage. Mercury concentrations were highly correlated among internal tissues (r2 > or = 0.89). Conversely, the relationships between Hg in feathers and internal tissues were substantially weaker (r2 < or = 0.42). Regression slopes sometimes differed among species and life stages, indicating that care must be used when predicting Hg concentrations in one tissue based on those in another. However, we found good agreement between predictions made using a general tissue-prediction equation and more specific equations developed for each species and life stage. Finally, our results suggest that blood is an excellent, nonlethal predictor of Hg concentrations in internal tissues but that feathers are relatively poor indicators of Hg concentrations in internal tissues.

Environmental Pollution Affects the Plumage Color of Great Tit Nestlings through Carotenoid Availability

Birds need to acquire carotenoids for their feather pigmentation from their diet, which means that their plumage color may change as a consequence of human impact on their environment. For example, the carotenoid-based plumage coloration of Great tit, Parus major, nestlings is associated with the degree of environmental pollution. Breast feathers of birds in territories exposed to heavy metals are less yellow than those in unpolluted environments. Here we tested two hypotheses that could explain the observed pattern: (I) deficiency of carotenoids in diet, and (II) pollution-related changes in transfer of carotenoids to feathers. We manipulated dietary carotenoid levels of nestlings and measured the responses in plumage color and tissue concentrations. Our carotenoid supplementation produced the same response in tissue carotenoid concentrations and plumage color in polluted and unpolluted environments. Variation in heavy metal levels did not explain the variation in tissue (yolk, plasma, and feathers) carotenoid concentrations and was not related to plumage coloration. Instead, the variation in plumage yellowness was associated with the availability of carotenoid-rich caterpillars in territories. Our results support the hypothesis that the primary reason for pollution-related variation in plumage color is carotenoid deficiency in the diet.

Contour feather moult of Ruffs Philomachus pugnax during northward migration, with notes on homology of nuptial plumages in scolopacid waders

Among the sandpiper family Scolopacidae, the Ruff Philomachus pugnax combines a large seasonal change in the appearance of the plumage with a very pronounced sexual plumage dimorphism. Studies on the east and south African wintering grounds of Ruffs indicate that before northward migration at least the males moult (part of) their basic (winter) plumage into a kind of alternative plumage. We studied the details of the subsequent moult into a final (supplemental) breeding plumage by quantifying the presence of three feather types—(1) winter (basic), (2) striped (alternate) and (3) breeding (supplemental)—in breast feather samples of 1441 Ruffs captured on staging areas in The Netherlands during northward migration in 1993-97. Ruffs arriving in March show a mix of winter and striped feathers. In April, the ‘breeding feather’ type appears in both male and female Ruffs, and partially takes the place of winter feathers as well as striped feathers in males, and winter feathers only in females. The presence of three plumages in Ruffs is thus confirmed for males, but also occurs in female Ruffs and in Bar-tailed Godwits Limosa lapponica. We suggest that striped feathers represent the ‘original’ alternative plumage feather type of the sandpiper family and that the showy feathers of the, in the European literature fortuitously appropriately named, ‘supplementary plumage’ represent an additional feather generation. Such colourful nuptial plumages could thus be derived characters that have evolved independently in several scolopacid genera, presumably under particularly strong sexual selection pressures.

Survival of postfledging Forster’s terns in relation to mercury exposure in San Francisco Bay

We examined factors influencing mercury concentrations in 90 fledgling Forster's terns (Sterna forsteri) and evaluated whether mercury influenced postfledging survival in San Francisco Bay, California. Mercury concentrations (+/- SE) in chicks 21-29 days old (just before fledging) were 0.33 +/- 0.01 microg g(-1) ww for blood and 6.44 +/- 0.28 microg g(-1) fw for breast feathers. Colony site had an overriding influence on fledgling contamination, however hatching date and age also affected blood, but not feather, mercury concentrations. Blood mercury concentrations decreased by 28% during the 50-day hatching period and increased with chick age by 30% during the last week prior to fledging. Using radio-telemetry, we calculated that cumulative survival during the 35-day postfledging time period was 0.81 +/- 0.09 (SE). Postfledging survival rates increased with size-adjusted mass, and cumulative survival probability was 61% lower for terns with the lowest, compared to the highest, observed masses. Conversely, survival was not influenced by blood mercury concentration, time since fledging, sex, or hatch date. Mercury concentrations in breast feathers of fledglings found dead at nesting colonies also were no different than those in live chicks. Our results indicate that colony site, hatching date, and age influenced mercury concentrations in fledgling Forster's terns, but that mercury did not influence postfledging survival.

Mercury concentrations in blood and feathers of prebreeding forster's terns in relation to space use of san francisco bay, california, usa, habitats

We examined mercury concentrations and space use of prebreeding Forster's terns (Sterna forsteri) in San Francisco Bay, California, USA, to assess factors influencing mercury levels in piscivorous birds. In 2005 and 2006, we collected blood and feathers from 122 Forster's terns and radio-marked and tracked 72 terns to determine locations of dietary mercury uptake. Capture site and capture date were the most important factors explaining variation in blood mercury concentrations (geometric mean +/- standard error: 1.09+/-0.89 microg/g wet wt), followed by sex and year. Accordingly, radiotelemetry data revealed that Forster's terns generally remained near their site of capture and foraged in nearby salt ponds, managed and tidal marshes, and tidal flats. In contrast, capture site and capture date were not important factors explaining variation in feather mercury concentrations, probably because feathers were grown on their wintering grounds several months prior to our sampling. Instead, sex and year were the most important factors explaining mercury concentrations in breast feathers (9.57+/-8.23 microg/g fresh wt), and sex was the most important factor for head feathers (6.94+/-7.04 microg/g fresh wt). Overall, 13 and 22% of prebreeding Forster's terns were estimated to be at high risk for deleterious effects due to mercury concentrations in blood (>3.0 microg/g wet wt) and feathers (>20.0 microg/g fresh wt), respectively. Breeding terns are likely to be even more at risk because blood mercury concentrations more than tripled during the 45-d prebreeding time period. These data illustrate the importance of space use and tissue type in interpreting mercury concentrations in birds.

Stable Isotopes (δD, δ13C, δ15N) Reveal Associations Among Geographic Location and Condition of Alaskan Northern Pintails

Abstract: Information on spring migration routes, geographic linkages among winter, spring, and breeding locations, and potential geographic effects on arrival body condition of northern pintails (Anas acuta) are currently unknown. Through a combination of stable‐isotope measurements of tissues representing different periods of dietary integration and body composition analyses, we examined these linkages for pintails breeding in Alaska, USA. We collected 77 females at 4 locations upon spring arrival. We performed carbon (δ13C), nitrogen (δ15N), and hydrogen (δD) isotope measurements on flight feathers, breast feathers, and whole blood, and we conducted body composition analyses. Inference based on stable‐isotope values in pintail tissues suggests that philopatry to Alaska was strong, as most of the collected females had stable‐isotope values consistent with the boreal forest of Canada or western Alaska and most spring migrating females had whole‐blood values indicating use of a food web in the boreal forest before collection. These patterns highlight the importance of the boreal forest for production and staging of pintails. Breast feather isotope values grown during prealternate molt were variable and covered the currently documented distribution of wintering pintails. Our results indicate associations among specific geographic areas, habitat use, and arrival condition of female pintails settling in Alaska. Females that wintered or staged in coastal habitat (as indicated by elevated δ13C values) arrived with less body fat compared to those that we inferred to have wintered or staged on inland freshwater habitat. Those females we inferred to use coastal areas appeared to rely more heavily on agricultural fields for nutrient acquisition (as indicated by elevated δ15N but low δ13C values). Our results provide the first link between low‐condition females and inferred use of specific geographic areas before arrival. Conservation on wintering grounds should focus on restoration and protection of wetland complexes that provide adequate natural food resources in proximity to coastal systems that are heavily used by wintering pintails. Conservation efforts should also focus on the boreal forest, not only for pintail, but for other boreal‐dependent species such as lesser scaup (Aythya affinis) (JOURNAL OF WILDLIFE MANAGEMENT 72(3):715–725; 2008)

Parental investment and its sensitivity to corticosterone is linked to melanin-based coloration in barn owls

Behavioral and physiological responses to unpredictable changes in environmental conditions are, in part, mediated by glucocorticoids (corticosterone in birds). In polymorphic species, individuals of the same sex and age display different heritable melanin-based color morphs, associated with physiological and reproductive parameters and possibly alternative strategies to cope with variation in environmental conditions. We examined whether the role of corticosterone in resolving the trade-off between self-maintenance and reproductive activities covaries with the size of melanin-based spots displayed on the ventral body side of male barn owls. Administration of corticosterone to simulate physiological stress in males revealed pronounced changes in their food-provisioning rates to nestlings compared to control males. Corticosterone-treated males with small eumelanic spots reduced nestling provisioning rates as compared to controls, and also to a greater degree than did corticosterone-treated males with large spots. Large-spotted males generally exhibited lower parental provisioning and appear insensitive to exogenous corticosterone suggesting that the size of the black spots on the breast feathers predicts the ability to cope with stressful situations. The reduced provisioning rate of corticosterone-treated males caused a temporary reduction in nestling growth rates but, did not affect fledgling success. This suggests that moderately elevated corticosterone levels are not inhibitory to current reproduction but rather trigger behavioral responses to maximize lifetime reproductive success.

Preen waxes do not protect carotenoid plumage from bleaching by sunlight

The plumage coloration of wild birds often changes during the breeding season. One of the possible reasons for this is that sunlight, and particularly ultraviolet (UV) wavelengths, degrades the pigments responsible for plumage coloration. It has been suggested that birds may apply preen wax to feathers to protect feathers from bleaching. This hypothesis is tested by exposing carotenoid‐based breast feathers of Great Tits to ambient light, light filtered to exclude UV and darkness. Preen waxes were experimentally removed from feather samples and the effect of light on coloration of treatment and control feathers compared. Ambient light had an effect on feather colour but preen wax did not. Feathers exposed to sun gradually became less saturated and hues shifted towards shorter wavelengths. This was not apparent in control feathers kept in darkness. Feathers exposed to full‐spectra sunlight faded more than those that were kept in light with UV wavelengths removed. There was a decrease in brightness of feathers in both experimental and control groups, which was assumed to be an effect of dirt accumulation. This experiment confirmed earlier suspicions regarding the detrimental effects of UV irradiation on carotenoid‐based coloration of avian feathers but failed to show any protective function of preen waxes. The possible consequences of these mechanisms of colour change for birds with regard to mating strategies are discussed.

Two pieces of information in a single trait? The yellow breast of the great tit (Parus major) reflects both pigment acquisition and body condition

Carotenoid-based plumage coloration has been shown to be dependent both on pigment content and feather structure. Against this background, we predict a relationship between feather pigment content and plumage hue. Furthermore, given the susceptibility of chroma to developmental perturbation of feather structure, we predict body condition to be related to chroma. We tested these predictions in the great tit, Parus major. Carotenoid content in yellow breast feathers was analysed by high-performance liquid chromatography (HPLC). Lutein was the main carotenoid contained in great tit feathers, followed by zeaxanthin. The hue of the feathers was accurately predicted from their lutein concentration, and chroma was predicted from the body condition value. Our data suggest that plumage coloration in the great tit could independently provide information on the ability of the signaller to collect carotenoids (via hue) and body condition (via chroma). Published results both from the great tit and other species support this view.

Sexual, seasonal, and environmental variation in plasma carotenoids in great tits, Parus major

In many birds, carotenoids have dual functions as irreversible plumage pigments and as physiologically essential vitamins and antioxidants. They must be obtained through the diet and may therefore be a limiting resource, a constraint that is likely to vary with factors such as sex, habitat, and time of year. In the present study, we investigated signs of carotenoid limitation in great tits, Parus major, in relation to sex, season, year, and within an urban versus a rural habitat. The two main carotenoids, lutein and zeaxanthin, were analysed by high-performance liquid chromatography in the plasma and in the yellow carotenoid-based breast feathers. We found that plasma carotenoid concentrations were significantly influenced by sex, season, and year, but not by urban versus rural habitat. At moult, plasma concentration was positively correlated with feather pigmentation, independent of body condition and sex. During the breeding season, however, circulating carotenoid concentrations were negatively related to the feather pigmentation (i.e. from previous autumn moult). We suggest that great tits are carotenoid deprived before leaf emergence, and that carotenoid utilization and limitations are sex-specific, but that there are neither any obvious honesty-maintaining costs of pigmentation, nor any fitness consequences of the colour variation. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 521–527.

Variation in the mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks in coastal saltpans, as revealed by stable isotopes

Causes of variation in mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks were studied through analysis of stable isotope ratios of carbon and nitrogen. Blood and breast feathers were collected from chicks in coastal saltpans during successive breeding seasons. Detritus samples and potential prey (macroinvertebrates) were also collected. Total mercury concentrations and stable isotope signatures were measured using atomic absorption spectroscopy and isotope ratio mass spectrometry respectively. Mercury levels in Chironomidae, Corixidae and Hydrophilidae correlated with mercury levels in chick feathers. Differences of δ 15N signatures between macroinvertebrate groups indicated that they belong to different trophic levels. δ 15N signatures of invertebrates correlated with mercury levels in invertebrates and chicks, but not with δ 15N signatures in chicks. Between-group and between-site differences of δ 15N signatures and mercury levels in invertebrates suggested that they contribute differently to mercury mobilization into chicks, and their relative contribution depends on prey availability in each site. Inter-site differences in the biomagnification factor reinforced that idea. δ 13C signatures in invertebrates marked a larger range of carbon sources than just detritus. Variation of water inflow regime and prey availability may cause between-group and between-site differences of δ 13C signatures in prey. Discrepancies between feather and blood for δ 13C signatures in Praias-Sado and Vaia suggested that temporal variation of prey availability may be the main factor affecting mercury mobilization into chicks in both those cases, since their water inflow regimes are the same. The lowest levels of δ 13C signatures in Vau suggested that water inflow regime may be the main factor in this case, since no discrepancy existed in δ 13C signatures between blood and feather.