On a warm day in late April, Frank Gallo is getting his steps in at one of his regular haunts: the sewage plant. He strolls along the paved trail outside the facility in Norwalk, Conn., scanning the pines on the left, the river on the right. Overhead eight Northern Rough-winged Swallows wheel in the cloudless sky, taking turns swooping into the water-treatment tanks to catch insects drawn to the nutrient-rich pools below. A Yellow Warbler belts out its not so humble brag—sweet sweet sweet I'm so sweet.