After birding several spring migrations on the East Coast, you might start to notice some patterns. Species don’t show up in April and May all mixed up in an avian potpourri; instead, they tend to pass through in a predictable order year after year. No one knows this better than banders at Ohio’s Black Swamp Bird Observatory (BSBO). Situated on Erie’s lakeshore, BSBO is one of the last places migrants can rest before crossing the Great Lakes for breeding grounds in Canada. When they alight to refuel, some hit mist nets set up in the vegetation below. Trained experts remove birds, take measurements, place a band around an ankle, and then send them on their way. “It’s a whirlwind,” says lead bander Ryan Jacob, who has worked these nets since 2009 when he began as a volunteer. “People’s memories are terrible,” he says, so it’s important to have data. And BSBO has a lot of it: Since 1992 they’ve banded 225,000 spring migrants—an average of 7,000...