Tree swallows are a useful bird species to measure exposure and effects of environmental contaminants:

1. They are widely distributed throughout the United States,
2. They will nest in boxes,so they can be attracted to study areas,and
3. They feed near their nest box on emergent aquatic insects.

Aquatic insects emerge from river sediments, so the swallows' tissues reflect levels of contaminants in sediments.

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Contaminant Effects on Tree Swallows: A Nationwide Indicator Species