| Summary: | Anthropogenic and natural stressors can affect ecosystems negatively and it is therefore important to have a clear understanding of the responses of organisms to stressors. The Northern Goshawk (Accipiter gentilis) is a common raptor species of the boreal forest ecosystem and its location at the top of its food chain makes it a special target for two important stressors; endoparasitism and environmental contaminants. The present study examined potential effects of these two stressors on morphological traits of Northern Goshawk nestlings in Troms County, Norway. A randomly assigned group of nestlings was treated with an anti-helminthic drug while a control group was placebo treated. In all nestlings, blood residues of a set of environmental contaminants were measured. The effects of anti-helminth treatment and contaminant concentrations on the size of morphological traits were assessed using statistical models. Nestlings of the treated group showed increased tail growth while the other morphological traits were unaffected by anti-helminth treatment. Further, no negative effects of the measured contaminant concentrations on morphological traits were found. There was, however, a positive relationship between tail growth and contaminant concentrations which may be interpreted as a result of the quality or quantity of the diet rather than an effect of contaminants. The findings may either imply that stress due to both helminths and environmental contaminants was rather low in the Northern Goshawk nestlings in the study area or that morphological traits are poor indicators for the stressors investigated.
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