The value of studying birds extends beyond the field of ornithology. Some species can be also used as indicators for ecological health and environmental monitoring. In this interactive story map created by the US Geological Survey (USGS), readers can explore how tree swallows are being used to help assess and monitor specific locations for the presence of legacy contaminants, such as pesticides and dioxins, that may have been released as far back as the 1950s. As the story map explains, tree swallows will nest in "highly industrial and urban locations where other species are often rare" and feed on insects that spend part of their lives in lake sediments, where contaminants tend to collect. Here, readers can learn about the different study sites, which include 27 areas of concern as well as 10 reference locations, and also view maps and summaries of the study's findings for each category of contaminants. The principal investigators of this study are Thomas Custer and Christine Custer, research wildlife biologists with the USGS Upper Midwest Environmental Sciences Center. This project is part of the Great Lakes Restoration Initiative, an ongoing multi-agency effort launched in 2010 to protect and restore North America's Great Lakes.