When Amy Musante catches the bubbly song of the Bobolink in spring, she hops into her SUV at dawn and heads to a hayfield on her 185-acre farm in western Massachusetts. She likes to watch the birds as the sun comes up, tinting Day Mountain in the middle distance a rosy orange color. “You always hear them before you see them,” says Musante, who moved east from California five years ago to revive her family’s operation. Musante has more than a passing interest in the striking black-and-white birds. She is participating in an effort to help the ground-nesters successfully breed. Among the longest-migrating songbirds in the Western Hemisphere, Bobolinks travel from wintering grounds as far south as Argentina’s rice fields and nest in U.S. and Canada grasslands. Centuries ago, the birds moved into the Northeast as forests were cleared for farmland. At first, they thrived. But later, as farmers began mowing hayfields more often, tractors interrupted the 9- to 11-week window...