Heavy metal pollution and blackheaded gull (larus ridibundus L.) breeding ecology

Abstract

Heavy metals in air, soil and water are a global problem and present a growing threat to the environment. These metals may have profound consequences for birds and can cause a number of sub-lethal effects, such as decreased reproductive success. The concentrations of selected heavy metals (As, Cd. Co, Cu, Fe, Pb, Mn, Ni, V, Zn) and Se in eggs and feathers from populations of black-headed gulls (Larus ridibundus L.) located on different colonies in the UK, which have different characteristics and are subject to different sources, types and degrees of pollution, were examined. Concentrations of As, Cu, Pb, Ni, Se and V measured in black-headed gull eggs were consistently high relative to those reported in previous field studies with other gull species. However, no significant effect was observed on the egg characteristics in terms of egg size and dimensions, shell thickness and index as a result of concentrations of metals measured in this study. Concentrations of Co, Fe and Ni were significantly negatively correlated with yolk:albumen ratio in the egg. The usefulness of sampling eggs to provide a reflection of local contamination has been demonstrated, with concentrations related to local sources of metal pollution and site differences reflected in sediment concentrations from previous studies. The importance of taking into account diffuse and historical pollution in addition to point source discharges has also been highlighted. As, Fe, Mn, Pb, Se, V and Zn were found at significantly higher concentrations in egg contents than egg shell, and Cd, Co and Ni concentrations were higher in shell than contents. Cu was distributed approximately equally. Within the egg contents, concentrations of As, Cu, Se and V were higher in the albumen than in the yolk, and Co, Fe, Mn, Ni, Pb and Zn concentrations were higher in the yolk than the albumen. Cd was found mainly in the shell and concentrations in egg contents were largely undetectable. Comparisons were made between a colony subject to high-level commercial egg harvesting and an un-harvested site, and between pre- and post-harvesting eggs on the harvested site. Postcollection eggs were found to be of significantly lower quality than the pre-collection eggs and the eggs from the uncollected site, as indicated by yolk:albumen ratio. Concentration of metals in eggs as a result of relaying forced by commercial harvesting has been demonstrated, with concentrations of Co, Fe and Ni significantly higher in post-collection eggs compared to precollection eggs. Average nesting density was significantly lower on the collected colony than the uncollected colony. No effect on egg size was found as a result of changes in nesting density. Concentrations of metals in black-headed gull chick down were measured and compared to egg data in order to assess the usefulness of feathers as a tool for non-destructive monitoring of metal pollution. The results suggest that feathers may be good indicators for As and Zn, and possibly also for Mn and Ni. However, the sample masses were very small and for a number of metals concentrations were largely undetectable using the analytical equipment available in this study. Future work with larger samples of down would be prudent to further examine the use of chick down to provide an indication of the level of pollution to which birds are exposed. The importance of using appropriate washing procedures to remove exogenous contamination of feathers to assess internal concentrations has been demonstrated

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