This sparrow has an orange-yellow face, a short, rounded tail and pointed tail feathers. Credit: USFWS   Mist netting is a popular and important tool to capture birds for research and monitoring. Credit: USFWS

The Saltmarsh Sparrow: An alarm for mercury contamination?

The Problem and Effects:
The saltmarsh sparrow (Ammodramus caudacutus) is found only in salt marshes along the Atlantic coastline. National Audubon Society has placed the songbird on its watch list, and the U.S. Fish and Wildlife Service considers it to be a "Bird of Conservation Concern." They forage on the ground or in marsh vegetation, sometimes probing in mud, and they eat mainly insects, aquatic invertebrates and seeds. The bird's diet is reflected in mercury levels in its blood. Thus, sparrows are excellent indicators of mercury contamination in estuaries of the Northeast.

Wildlife exposed to certain levels of mercury can experience reproductive failure, impaired muscular coordination, behavior abnormalities, abnormal vocalization, vertigo, convulsions, paralysis and death.

What We're Doing:
To find out if mercury is a potential problem for breeding saltmarsh sparrows, the Service partnered with BioDiversity Research Institute to capture sparrows on five National Wildlife refuges in southern Maine, northeastern Massachusetts, coastal Rhode Island, coastal Connecticut, and Long Island, New York, from 2004 to 2010.

Birds were captured from June to August using mist nets, and blood was collected for mercury analysis. Results showed that mercury levels in the blood of adult sparrows were significantly higher in birds captured from Parker River National Wildlife Refuge than from other refuges sampled, and the mercury contamination may be impacting the overall health of this songbird species. Our continuing research attempts to identify potential point sources of mercury that might explain the elevated levels at Parker River.

Mercury accumulates at potentially harmful rates in populations on breeding sites, so researchers wondered whether the same problem occurs in areas where the sparrows go during winter. The Service partnered with the Center for Conservation Biology at the College of William and Mary to assess mercury levels in sparrows on wintering areas at several National Wildlife Refuges in Virginia.

The results to date suggest that saltmarsh sparrows, which nest along the northeastern coast of North America, lower their mercury levels when they migrate to wintering grounds along the southeastern coast. This may be due to a shift in diet downwards on the food chain, for example, fewer insects and more seeds.

But it may also reflect lower environmental mercury levels.

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