On the most beautiful days of spring, Mary Shidel begins her rounds around 6 in the morning. As a banding assistant at the Powdermill Avian Research Center in rural Rector, Pennsylvania, it’s her job to collect migratory songbirds from several dozen mist nets hidden around the wooded, marshy property. She unfurls the nets around 5:45, and takes the next few hours to cycle through them, freeing and retrieving the birds that have flown in. Most of the time, the traps yield passerines: a male Common Yellowthroat tschat-tschat-tschatting, a handful of catbirds screeching their beaks off, an Indigo Bunting performing its frenzied routine. These species prove to be the best subjects; once they’re banded and deemed healthy, they can be tapped for a whole slew of studies, says Luke DeGroote, avian ecologist and Bird Banding Program coordinator at Powdermill. Bioacoustics, radar tracking, and bird-safe glass testing are just a few examples. The glass experiments, for one, may be the...