On a warm and buggy May evening, an Eastern Whip-poor-will’s brown, orange, and white mottled feathers blend in seamlessly with the brittle oak leaves she sits on. The bird is nearly impossible to differentiate from her surroundings. Grant Witynski, a biologist at the University of Illinois Urbana-Champaign, stands just a few feet away. As he and his technical assistant Olivia Moline inch closer, a stick snaps under foot. The bird flushes to a nearby branch just above the ground, her wings outstretched in defense, her flat head and whiskered face opposite her offenders. In the shallow indentation where she sat are two brown marbled eggs, the first seen by researchers this season. Witynski is part of an ongoing project to monitor whip-poor-wills in Central Illinois’s Sand Ridge State Forest, where prickly pear cacti lobes erupt from the ground and oak trees tower over patches of prairie. This study site is one of the few known places in the Midwest where the birds, one of...