Feather δ13C Values Research Articles

Accumulate or eliminate? Seasonal mercury dynamics in albatrosses, the most contaminated family of birds

Albatrosses (Diomedeidae) are iconic pelagic seabirds whose life-history traits (longevity, high trophic position) put them at risk of high levels of exposure to methylmercury (MeHg), a powerful neurotoxin that threatens humans and wildlife. Here, we report total Hg (THg) concentrations in body feathers from 516 individual albatrosses from 35 populations, including all 20 taxa breeding in the Southern Ocean. Our key finding is that albatrosses constitute the family of birds with the highest levels of contamination by Hg, with mean feather THg concentrations in different populations ranging from moderate (3.8 μg/g) to exceptionally high (34.6 μg/g). Phylogeny had a significant effect on feather THg concentrations, with the mean decreasing in the order Diomedea > Phoebetria > Thalassarche. Unexpectedly, moulting habitats (reflected in feather δ13C values) was the main driver of feather THg concentrations, indicating increasing MeHg exposure with decreasing latitude, from Antarctic to subtropical waters. The role of moulting habitat suggests that the majority of MeHg eliminated into feathers by albatrosses is from recent food intake (income strategy). They thus differ from species that depurate MeHg into feathers that has been accumulated in internal tissues between two successive moults (capital strategy). Since albatrosses are amongst the most threatened families of birds, it is noteworthy that two albatrosses listed as Critical by the World Conservation Union (IUCN) that moult and breed in temperate waters are the most Hg-contaminated species (the Amsterdam and Tristan albatrosses). These data emphasize the urgent need for robust assessment of the impact of Hg contamination on the biology of albatrosses and they document the high MeHg level exposure of wildlife living in the most remote marine areas on Earth.

Moulting and Wintering Grounds of Marsh WarblersAcrocephalus palustris: Evidence from Stable Isotopes and Ring Recoveries

Abstract. We analysed stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in Marsh Warbler Acrocephalus palustris feathers sampled in Europe and Africa to assess non-breeding habitat selection and location of wintering grounds of different breeding populations. Feather δ13C values showed that Marsh Warblers occupy a biome dominated by C4 vegetation during the stopover in northeastern Africa, whereas C3 habitats are used during the complete moult in southern Africa. East European Marsh Warblers differed in their stable isotope profiles from other European regions, suggesting a certain level of population segregation in southern Africa. A dual-isotope assignment approach confirmed this difference and helped us restrict the autumn staging areas to lower elevations of the Ethiopian Highlands west of the Rift valley. Available ring recoveries, however, suggested high levels of population mixing both on migration through East Africa and in the final wintering grounds.

Stable Nitrogen and Carbon Isotopes May Not Be Good Indicators of Altitudinal Distributions of Montane Passerines

Abstract We examined δ15N and δ13C values of feathers from nine species, belonging to three feeding guilds (herbivores, omnivores, and insectivores), of wild passerines at eight sites along an altitudinal gradient (339–2,876 m asl) within Taroko National Park, Taiwan. We examined: (1) if altitudinal patterns in feather δ15N and δ13C are consistent with previously published values for plants and soils, (2) if feather δ15N and δ13C differ among sites, and (3) if there are year-to-year and/or month-to-month fluctuations in feather δ15N and δ13C of the same birds. We found no simple relationship between feather isotope values and altitude. Feather δ15N values decreased significantly with increasing altitude for insectivores, but not for herbivores and omnivores. Feather δ13C values increased significantly with increasing altitude for herbivores and omnivores, but not for insectivores. Altitudinal trends in feather δ15N and δ13C values exhibit even more inconsistent patterns when data were analyzed by species;...

Comparative foraging ecology and ecological niche of a superabundant tropical seabird: the sooty tern Sterna fuscata in the southwest Indian Ocean

Over 6-million pairs of sooty terns Sterna fuscata breed once a year in the southwest Indian Ocean, mostly on three islands of the Mozambique Channel (Europa, Juan de Nova and Glorieuses) and in the Seychelles region. Seasonal reproduction in either winter or summer is the dominant strategy in the area, but non-seasonal reproduction also occurred in some places like at Glorieuses Archipelago. The feeding ecology of the sooty tern was investigated during the breeding seasons to determine whether terns showed significant differences in their trophic ecology between locations. Regurgitations were analyzed to describe the diet of individuals when breeding, and stable isotopes and mercury concentrations were used to temporally integrate over the medium-term of the trophic ecology of both adults and chicks. Overall, the diet was composed of fish, flying squid and fish larvae in different proportions. At Europa and Aride in the Seychelles, where winter reproduction occurs, large epipelagic prey like flying fish or squid dominated the diet. At Juan de Nova, sooty terns reproduce in summer and rely mostly on fish larvae. At Glorieuses (non-seasonal breeding), the diet was intermediate with fish larvae and flying squid being important prey items. The stable-carbon and nitrogen isotope values in blood confirm the differences observed in dietary analysis, and demonstrate different feeding strategies between colonies. δ13C values of feathers showed spatial segregation between birds from the Mozambique Channel and the Seychelles region. Terns from the Seychelles had also higher δ15N values. Feather δ13C values also suggest a significant shift from summer to wintering habitat for birds from Juan de Nova. This study emphasizes the high phenotypic plasticity of the species, which may explain its numerical dominance in all tropical waters of the World’s Ocean.

CHERNOBYL AS A POPULATION SINK FOR BARN SWALLOWS: TRACKING DISPERSAL USING STABLE-ISOTOPE PROFILES

Stable-isotope profiles of feathers can reveal the location or habitat used by individual birds during the molting period. Heterogeneity in isotope profiles will reflect heterogeneity in molt locations, but also heterogeneity in breeding locations, because spatial heterogeneity in molt locations will be congruent with spatial heterogeneity in breeding locations in species with high connectivity between breeding and molting sites. We used information on the congruence of spatial heterogeneity in molt and breeding location to study population processes in Barn Swallows (Hirundo rustica) from a region. near Chernobyl, Ukraine, that has been radioactively contaminated since 1986; from an uncontaminated control region near Kanev, Ukraine; and from a sample of pre-1986 museum specimens used to investigate patterns prior to the nuclear disaster at Chernobyl, from both regions. Previous studies have revealed severe reductions in Barn Swallow reproductive performance and adult survival in the Chernobyl region, implying that the population is a sink and unable to sustain itself. Female Barn Swallows are known to disperse farther from their natal site than males, implying that female stable-isotope profiles should tend to be more variable than profiles of males. However, if the Barn Swallows breeding at Chernobyl are not self-sustaining, we would expect males there also to originate from a larger area than males from the control region. We found evidence that the sample of adult Barn Swallows from the Chernobyl region was more isotopically heterogeneous than the control sample, as evidenced from a significant correlation between feather sigma13C and sigma15N values in the control region, but not in the Chernobyl region. Furthermore, we found a significant difference in feather sigma15N values between regions and periods (before and after 1986). When we compared the variances in sigma13C values of feathers, we found that variances in both sexes from post-1986 samples from Chernobyl were significantly larger than variances for feather samples from the control region, and than variances for historical samples from both regions. These findings suggest that stable-isotope measurements can provide information about population processes following environmental perturbations.

Linking Breeding and Wintering Grounds of Bicknell's Thrushes Using Stable Isotope Analyses of Feathers

AbstractPrevious studies have shown that natural abundance of deuterium (D), and to a lesser extent 13C, in feathers of migrant songbirds in North America can be used to infer geographic origins of molt. We used that approach to investigate whether Bicknell's Thrush (Catharus bicknelli) populations could be segregated on the breeding grounds at six sites in eastern North America to evaluate contributions from the breeding areas to wintering populations. Further, we tested our isotopic model using feathers from hatching-year migrant Swainson's Thrush (Catharus ustulatus) and Gray-cheeked Thrush (Catharus minimus) moving through southern Manitoba and Ontario and found that δD values were consistent with northerly boreal forest natal sites in northwestern and central Canada. Despite a strong latitudinal gradient in δD of average growing season precipitation over the breeding range, we found considerable overlap in δD values of Bicknell's Thrush among all breeding sites. No strong pattern in δ13C values of feathers with latitude was apparent. Nevertheless, the more negative δD values of feathers from wintering birds in the Dominican Republic compared to breeding area samples suggested that birds from more northerly locations in North America contributed to this population of wintering birds. High variance in feather δD values within breeding populations also suggested high natal dispersal, considerable movement of birds among island habitats on the breeding grounds, or both. Even higher variances in feather δD values from small study areas on the wintering grounds, compared to similar-sized areas in the breeding range, suggest that many different breeding populations mix in winter habitat.