Biological clocks are found in any animal, from worms and flies up to humans, says Paul Bartell, assistant professor of avian biology. Working in concert with daylight and other environmental cues, these innate regulators control not just patterns of sleeping and eating, but hormone releases and many other cell processes as well. In songbirds, they dictate the delicate timing of migration.

George Young tracks birds. He begins with satellite data: maps of yellow, green, and red blobs indicating the heat that radiates from grassy fields, patches of shrubbery, and parking lots. From experience, Young knows which birds live in those habitats. "In grassy areas you might see a short-eared owl or a horned lark," he says.

The breeze blowing off Lake Erie seems premature, far too soon and too cool for dusk on an early September evening. Yet before Erie's inland feels the chill, autumn comes to Presque Isle State Park, the "almost island" that jets out like a hook into the waters of the Great Lake. The vivid colors of the beach's summer sky have already muted: The setting sun today is draped by a layer of clouds, the dark blue water, as if shaded by a child's crayon, blending smoothly into a gray horizon.