Cust_Chri_001_springsummer2011_003_l.jpg
![Tree swallow sitting on a fence post](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/full_width/public/media/images/Cust_Chri_001_springsummer2011_003_l.jpg?itok=4KIzr-14)
Detailed Description
Tree swallows have been used extensively for monitoring the exposure and effects of environmental contaminants because they feed on aquatic insects; concentrations of contaminants in eggs reflect sediment contamination.
Sources/Usage
Public Domain.