Molted feathers indicate low mercury in bald eagles of the Chesapeake Bay, USA

Mercury is a potent neurotoxin affecting birds and other wildlife worldwide. Bald eagles (Haliaeetus leucocephalus) are vulnerable to mercury bioaccumulation because they are high in the food web and associated with aquatic ecosystems prone to mercury methylation. Eagle populations, long endangered in the continental United States by contaminants and persecution, are recovering throughout their range. We used single adult eagle feathers collected near 83 occupied nests to show that mercury levels in the Chesapeake Bay eagle population are the lowest in North America (3.82 ± 5.15 μg/g dry weight). We then used 20 feathers from each of 20 salvaged eagles to calculate a confidence interval around the estimate based on single feathers from nesting eagles. Using an inexpensive and non-invasive method to assess mercury burdens we have demonstrated that few Chesapeake Bay bald eagles were above levels suspected of causing reproductive or survival effects in birds.

▸ Single feathers from near Chesapeake Bay eagle nests were sampled for mercury. ▸ This breeding eagle population had lowest level of mercury recorded in USA. ▸ Few individuals in this population are likely to experience effects of mercury. ▸ Sampling just 5 feathers provides an estimate within 10% of individuals’ plumage.