Using bird feathers to measure mercury in the environment: relationships between mercury content and moult.
Feathers can be used to monitor mercury levels in marine, freshwater and terrestrial ecosystems. Previous studies have often failed to take into account the great differences in mercury levels between feathers of individual birds. Feathers replaced early in the moulting sequence have higher levels of mercury than those moulted later. The widely held idea that mercury levels in feathers reflect dietary intake at the time of feather growth is not supported by our data. We suggest that the amount of mercury stored in body tissues is the main factor determining levels in plumage. Although they are most often used, remiges and rectrices may not be the most suitable feathers if mercury levels in birds are to be examined: body feathers provide the most representative sample for estimating whole-bird mercury content.