Herons on the lower Columbia and Willamette do not migrate, so the residue in eggs is from local contamination. And, they are relatively insensitive to pollutants and are able to reproduce while carrying high contaminant loads. So in 1994, with a grant from the U.S. Fish and Wildlife Service, Carmen Thomas began the comprehensive research project, with Anthony as her advisor. It would be the basis for her master's thesis. During the next two years, she collected and chemically analyzed eggs and embryo liver tissue and observed heron behavior from birth to the fledgling stage of development, all in hopes of determining effects on herons and, ultimately, helping the bald eagle.
Herons pick a nesting site based on food sources, and they can adapt to various kinds of sites.
The birds also tend to be devoted to sites they used in previous years. These can be spots like a quiet, mosquito-clouded riverside or an urban island with a noisy gravel dredging operation nearby. Both figured into the final mix of a half-dozen study sites. While two sites along the Willamette, near Portland, do not have bald eagles living in the neighborhood, three others along the Columbia and one in Puget Sound do. On the Willamette, Thomas focused on heron colonies at Molalla State Park and on Ross Island.