Population-level plasticity in foraging behavior of western gulls (Larus occidentalis).

BACKGROUND: Plasticity in foraging behavior among individuals, or across populations may reduce competition. As a generalist carnivore, western gulls (Larus occidentalis) consume a wide range of marine and terrestrial foods. However, the foraging patterns and habitat selection (ocean or land) of western gulls is not well understood, despite their ubiquity in coastal California. Here, we used GPS loggers to compare the foraging behavior and habitat use of western gulls breeding at two island colonies in central California. RESULTS: Gulls from offshore Southeast Farallon Island (SFI; n = 41 gulls) conducted more oceanic trips (n = 90) of shorter duration (3.8 ± 3.3 SD hours) and distance (27.1 ± 20.3 km) than trips to the mainland (n = 41) which were nearly 4 times longer and 2 times farther away. In contrast, gulls from coastal Año Nuevo Island (ANI; n = 20 gulls) foraged at sites on land more frequently (n = 103) but trip durations (3.6 ± 2.4 h) and distances (20.8 ± 9.4 km) did not differ significantly from oceanic trips (n = 42) where trip durations were only slightly shorter (2.9 ± 2.7 h) and equidistant (20.6 ± 12.1 km). Gulls from both colonies visited more sites while foraging at sea but spent significantly longer (3-5 times) durations at each site visited on land. Foraging at sea was also more random compared to foraging trips over land where gulls from both colonies visited the same sites on multiple trips. The total home range of gulls from SFI (14,230 km2) was 4.5 times larger than that of gulls from ANI, consistent with greater resource competition resulting from a larger abundance of seabirds at SFI. CONCLUSIONS: Population-level plasticity in foraging behavior was evident and dependent on habitat type. In addition, gulls from SFI were away foraging longer than gulls from ANI (22% vs. 7.5%, respectively), which impacts the defense of territories and attempts at nest predation by conspecifics. Our results can be used to explain lower chick productivity at SFI, and can provide insight into increased gull activity in urban areas.

Trace Element Concentrations in Relation to the Trophic Behaviour of Endangered Ivory Gulls (Pagophila eburnea) During Their Stay at a Breeding Site in Svalbard.

The ivory gull is a high-Arctic species considered endangered in most parts of its breeding range. Ivory gulls must cope with both the reduction of sea ice cover triggered by climate change and increasing contaminant loads due to changes in global contaminant pathways. The objective of this study was to assess the concentration of 14 essential and nonessential trace elements at four colonies of ivory gulls breeding on Barentsøya, Svalbard, and the relationship between contaminant exposure and the diet of individuals. Contaminants and stable isotopes (δ15N, δ13C) were determined in blood (red blood cells and whole blood), and feathers of ivory gulls collected over several years. The most quantitatively abundant nonessential trace element found in the ivory gull was mercury (Hg). Selenium (Se) was present in substantial surplus compared with Hg, which would imply relative protection against Hg toxic effects but raises concern about Se potential toxicity. Moreover, other elements were detected, such as silver, arsenic, cadmium, and lead, which would warrant monitoring because of the potential additive/synergetic effects of these compounds. This study demonstrated individual differences in trophic behaviour that triggered discrepancies in Hg concentrations, highlighting the potential biomagnifying ability of this metal in the ivory gull's food web. Results highlighted the mixing of birds coming from different geographical areas on Barentsøya.

Circumpolar contamination in eggs of the high-Arctic ivory gull Pagophila eburnea.

The ivory gull Pagophila eburnea is a high-Arctic species threatened by climate change and contaminants. The objective of the present study was to assess spatial variation of contaminant levels (organochlorines [OCs], brominated flame retardants [BFRs], perfluorinated alkyl substances [PFASs], and mercury [Hg]) in ivory gulls breeding in different areas across the Arctic region as a baseline for potential future changes associated with climate change. Contaminants were already determined in eggs from Canada (Seymour Island; except PFASs), Svalbard in Norway (Svenskøya), and 3 sites in Russia (Nagurskoe, Cape Klyuv, and Domashny). New data from Greenland allowed the investigation of a possible longitudinal gradient of contamination. The most quantitatively abundant OCs were p,p'-dichlorodiphenyldichloroethylene (DDE) and polychlorobiphenyls. Mercury concentrations were higher in Canada compared with other colonies. Eggs from Nagurskoe often were characterized by higher OC and BFR concentrations. Concentrations gradually decreased in colonies situated east of Nagurskoe. In contrast, PFAS concentrations, especially perfluorooctanoate and perfluorononanoate, were higher in Greenland. Some of the contaminants, especially Hg and p,p'-DDE, exceeded published thresholds known to disrupt the reproductive success of avian species. Overall, the levels of OCs, BFRs, and PFASs did not suggest direct lethal exposure to these compounds, but their potential synergetic/additive sublethal effects warrant monitoring.

Evidence of species-specific detoxification processes for trace elements in shorebirds.

This study investigated sub-lethal effects and detoxification processes activated in free-ranging Red Knots (RKs) (Calidris canutus) from the Pertuis Charentais on the Atlantic coast of France, and compared the results with previous data obtained on another shorebird species, the Black-tailed Godwit (Limosa limosa). The concentrations of 13 trace elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Zn) were assessed in the liver, kidneys, muscle and feathers. Stable isotope analyses of carbon and nitrogen were carried out to determine whether differences in diet explained variations in elemental uptake. The mRNA expression of relevant genes (cytochrome c oxidase 1, acetyl-CoA carboxylase, Cu/Zn and Mn superoxide dismutase, catalase, metallothionein, malic enzyme), antioxidant enzyme activities (catalase, glutathione peroxidase (GPx), superoxide dismutase), and metallothionein (MT) levels were investigated to shed light on trace element detoxification and toxic effects. Although Red Knots were characterized by elevated As and Se concentrations which were potentially toxic, most elements were usually below toxicity threshold levels. The results strongly suggested a dietary specialization of Red Knots, with individuals feeding on higher trophic status prey experiencing higher As, Hg and Se burdens. Red Knots and Godwits also showed discrepancies in elemental accumulation and detoxification processes. Higher As and Se concentrations in Red Knots enhanced catalase gene expression and enzyme activity, while Godwits had higher Ag, Cu, Fe and Zn levels and showed higher MT production and GPx activity. The results strongly suggest that detoxification pathways are essentially trace element- and species-specific.

Insight on trace element detoxification in the Black-tailed Godwit (Limosa limosa) through genetic, enzymatic and metallothionein analyses.

Trace element concentrations (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Zn) were investigated in the liver, kidneys, muscle and feathers of 31 black-tailed godwits (Limosa limosa) accidentally killed during catches by mist net in the Pertuis Charentais, Atlantic coast of France. Analyses of carbon and nitrogen stable isotope ratios were carried out in liver, muscle and feathers in order to elucidate dietary patterns and to determine whether differences in diet explained the variation in elemental uptake. This study also aimed to have a preliminary assessment of sub-lethal effects triggered by trace elements through the investigation of gene expressions by quantitative real-time PCR, antioxidant enzyme activities (catalase, superoxide dismutase, glutathione peroxidase), and metallothionein (MT) levels. The results showed that Cr and Ni concentrations in tissues of adults were lower than in juveniles in part because adults may have eliminated these trace elements through moulting. Except for Cd and Ni, trace element concentrations were negatively correlated to the body mass of godwits. Ag, As, Hg and Se concentrations were positively linked with the trophic position of birds. The diet could be considered as a fundamental route of exposure for these elements demonstrating therefore the qualitative linkage between dietary habits of godwits and their contaminant concentrations. Our results strongly suggest that even though trace element concentrations were mostly below toxicity threshold level, the elevated concentrations of As, Ag, Cd, Cu, Fe and Se may however trigger sub-lethal effects. Trace elements appear to enhance expression of genes involved in oxidative stress defence, which indicates the production of reactive oxygen species. Moreover, birds with the highest concentrations appeared to have an increased mitochondrial metabolism suggesting that the fight against trace element toxicity requires additional energetic needs notably to produce detoxification mechanisms such as metallothioneins.

Effects of dietary cadmium contamination on bird Anas platyrhynchos--comparison with species Cairina moschata.

This study aimed to assess the effect of two dietary cadmium (Cd) levels (C1: 1 mgkg(-1); C10: 10 mgkg(-1)) on bird Anas platyrhynchos exposed for 10, 20 and 40 days (5 animals per experimental condition). Ducks were able to accumulate high amounts of Cd, especially in kidneys (after 40 days: C1 8.1 ± 1 mgkg(-1), C10 37.7 ± 4.3 mgkg(-1)). After 40 days, the lowest Cd level triggered oxidative stress and stimulated mitochondrial metabolism. At the same time, highest amounts of Cd (C10 group) only triggered repression of genes encoding for catalase and acetyl-CoA carboxylase, with repression factors of 1/50 and 1/5, respectively. High dose exposures were then associated with the repression of genes encoding for antioxidant, whereas low dose exposure triggered their induction. In contrast, the onset of MT gene expression appeared quickly for the C10 group even if a time delay was observed between gene expression and protein accumulation. Through the comparison of A. platyrhynchos and Cairina moschata, the response to Cd toxicity appeared species-dependent. Discrepancies between species could be explained by differential utilization of MT. This pathway of detoxification seemed sufficient to counter Cd toxicity.

Effect of dietary cadmium on lipid metabolism and storage of aquatic bird Cairina moschata.

In environment, birds often fast in connection with breeding, migration or drastic climatic conditions and need to mobilize lipid reserves during these periods. The impairment of lipid metabolism by cadmium (Cd; 1 mg kg(-1) added in diet) was investigated on palmiped Cairina moschata. Expression levels of genes involved in lipid metabolism, mitochondrial metabolism and detoxification were investigated in liver and muscle of ducks. Lipid content in muscle and liver were analysed and plasma triglycerides were quantified. After 20 days, ducks exposed to Cd displayed a lower body weight and lower lipid content in liver than controls. In muscle, the increase of lipid content was only significant for control ducks but not for exposed ducks. Exposed ducks appeared unable to sufficiently transport and store lipids into peripheral tissues. Cd impairs lipid metabolism by several ways. First, Cd triggered the down-regulation of fatty acids synthesis in liver even if the NADPH production and the mitochondrial metabolism are enhanced, suggesting a stronger energy needs. Secondly, the associated decrease of plasma triglycerides and lipoprotein lipase activity with Cd are consistent with impairment of lipids storage in peripheral tissues.

Trace element concentrations (mercury, cadmium, copper, zinc, lead, aluminium, nickel, arsenic, and selenium) in some aquatic birds of the southwest Atlantic coast of France.

Trace elements (mercury [Hg], cadmium [Cd], copper [Cu], zinc [Zn], lead [Pb], aluminium [Al], nickel [Ni], arsenic [As], and selenium [Se]) were investigated using inductively coupled plasma-mass spectrometry in liver, kidney, muscle, and feather of aquatic birds wintering or inhabiting the wetlands situated on the Southwest Atlantic coast of France. A majority of greylag geese, red knots, and grey plovers were collected from among hunter-shot animals. The relation between residue concentrations, age (juvenile vs. adult), and sex was investigated. Trace elements were lower than threshold levels of toxicity, except for Pb. Greylag geese sampled could be considered Pb-poisoned. These consequential levels of contamination could be the result of the ingestion of Pb-shot from ammunition used in hunting areas they crossed during migration. Cd accumulation increased with age, whereas Pb levels in feathers were lower in adult birds in connection with moulting. As was influenced by sex. Female birds displayed higher concentrations in liver and feathers than did male birds.

Impact of cadmium on aquatic bird Cairina moschata.

The impact on palmiped Cairina moschata of two levels of dietary cadmium (Cd) contamination (C1: 1 mg kg(-1) and C10: 10 mg kg(-1)) was investigated on liver gene expression by real-time PCR. Genes involved in mitochondrial metabolism, in antioxidant defences, detoxification and in DNA damage repair were studied. Metallothionein (MT) protein levels and Cd bioaccumulation were also investigated in liver, kidneys and muscle. Male ducks were subjected to three periods of exposure: 10, 20 and 40 days. Cd was mainly bioaccumulated in kidneys first and in liver. The concentrations in liver and kidneys appeared to reach a stable level at 20 days of contamination even if the concentrations in muscle still increased. Cd triggered the enhancement of mitochondrial metabolism, the establishment of antioxidant defences (superoxide dismutase Mn and Cu/Zn; catalase) and of DNA repair from 20 days of contamination. Discrepancies were observed in liver between MT protein levels and MT gene up-regulation. MT gene expression appeared to be a late hour biomarker.

Cadmium uptake by the European eel: trophic transfer in field and experimental investigations.

Due to its status of threatened species and being heavily contaminated by metals, the European eel (Anguilla anguilla) was selected to investigate cadmium contamination levels of fish settled along a historically cadmium-contaminated hydrosystem, the Garonne-Gironde continuum (France), according to its various location sites and fish length. Results have shown an important site effect on cadmium concentrations in liver but not in gills, highlighting the possible predominance of the trophic exposure route. Subsequently, uncontaminated eels were experimentally exposed to cadmium by water uptake and/or trophic route(s). Eels were fed with different preys: white shrimps collected in an unpolluted area in the Gironde estuary, and cadmium-enriched shrimps. Data obtained tend to show that the use of cadmium-enriched food during experimental investigations triggers an underestimation of the metal trophic transfer rate. These two complementary approaches provide some elements to suggest that the trophic route plays an important role in cadmium contamination of wild eels.

Concentrations of metals (zinc, copper, cadmium, and mercury) in three domestic ducks in France: Pekin, Muscovy, and Mule ducks.

The role of different factors such as biological material (tissues, organs) and trophic condition (overfeeding or not) in the metal accumulation was studied in three genotypes of ducks (Pekin, Muscovy, and Mule) under breeding conditions. Results showed that overfeeding decreased the concentration in Cd, Cu, and Zn through the dilution process. In contrast, mercury concentration increased with this method. A relation between lipidic metabolism of genotypes and the distribution of this metal in biological material was found. Domestic ducks were little contaminated, but a low chronic contamination in Cd was observed, probably coming from the food. Due to the low levels of contamination observed in these breeding ducks, they can be considered as a good control for further contamination studies and comparison with accumulation levels recorded in the field. The impact of feeding condition on accumulation showed the importance of taking into account the life cycle of birds before studying their contamination and the impact of pollutants.