Mercury in breeding and wintering Nelson's Sparrows (Ammodramus nelsoni)

The objective of this study was to increase our understanding of Hg exposure in birds with obligate ties to coastal salt marsh and inland wetland systems. Many species filling such niches are of conservation concern because of reduced size and quality of vital habitats. We used Nelson's Sparrow (Ammodramus nelsoni) as an indicator of regional mercury (Hg) availability in its breeding and wintering salt marsh and wetland habitats. Blood, breast feathers and the first primary feather were sampled from Nelson's Sparrows wintering in North Carolina coastal salt marshes and breeding in wetland systems in North Dakota (A. n. nelsoni) and Ontario, Canada (A. n. alterus). Wintering Nelson's Sparrow breast feathers contained 3.0 times as much Hg as birds breeding in North Dakota and 2.4 times as much Hg as those breeding in Ontario. Breeding Nelson's Sparrows in North Dakota exhibited blood Hg levels 4.9 times as high as those from birds breeding along James Bay and 7.6 times as high as those wintering in North Carolina. These results provide significant insight on the timing of molt in this species as well as how Hg exposure varies regionally and seasonally for these birds. Further, our results provide a better understanding of how and where Hg exposure may be a threat to Nelson's Sparrows and other birds with obligate ties to aquatic systems.