© Marcel Burkhardt
Ganz, K. (2016)
Feathers as a temporal archive to study lead exposure and stress events in golden eagles (Aquila chrysaetos) - potential and constraints.
Master-Thesis, University of Zurich
Through human activities, a huge amount of chemicals and toxins is constantly brought into the environment with sometimes pervasive consequences. One of these contaminants is the heavy metal lead. Lead acts as a nonspecific poison affecting all body systems and belongs, due to human activities, to the most commonly found heavy metals in ecosystems. There are several cases of sub-lethal and lethal lead poisoning reported in golden eagles from the Swiss Alps and it is assumed that poisoning mainly happens through the ingestion of carcasses or offal from game shot with lead ammunition. However, how often and over which period such an uptake of lead takes place and whether lead has an effect on the stress axis in golden eagles is not yet known and belonged to the main questions of this study.
During growth, feathers incorporate lead and corticosterone, the main avian stress hormone, and thus represent a temporal archive of these substances. Therefore, lead and corticosterone concentration in feather segments of golden eagles were measured as they offer the possibility to infer the frequency and magnitude of lead uptake and the release of corticosterone during feather growth. Additionally, lead concentration in bones was measured to determine lifetime exposure to this heavy metal and abundance of fault bars in feathers was determined to assess overall exposure of the individuals to stress. Although lead concentration in bones was considerable, pointing at repeated lead uptake, almost no elevated lead levels were found in feathers, suggesting that lead uptake through ingestion of offal from lead shot game and moult happened at different times. Lead concentration between bones of the same individual differed widely in this study, suggesting that bones cannot be substituted for one another in comparative lead studies, as is generally assumed. Feather corticosterone was found to vary both within and between individuals, pointing at differences in stress exposure during feather growth. Prevalence of fault bars differed highly between individuals, giving further indications of differences in stress exposure history. Furthermore, in the single case where a lead exposure event was found in a feather, no correlation between lead and corticosterone concentration was found, indicating that sub-lethal lead poisoning did not lead to an immediate stress response.