In winter, flocks of wintering Snow Geese, Ross’s Geese, and Sandhill Cranes stop at Bosque del Apache National Wildlife Refuge in New Mexico. Just before sunrise, the geese are a mass of kinetic and potential energy, like a symphony orchestra tuning up for a big performance. Hunger might…

Bobolinks breed in North America and winter in South America. Like many songbirds, they’re classic long-distance migrants. But some Savannah Sparrows fly far south in winter, some fly not so far, and some stay put. This mix of strategies is known as “differential migration.” Sometimes…