WHAT IS THIS ENERGY that floods our veins in autumn? When the nights start turning cold and the trees are showing their first reds and yellows, I find myself rising at dawn and hurrying outside to cut firewood and install storm windows, then rushing off to spend the rest of the day fishing on rivers or hunting in the woods. Why so energetic? Why so restless?

Anthropologists say we’re a restless species, descended from nomads who followed the seasons in search of better hunting and foraging. We migrated on foot across entire continents, crossed ice-bridges to new continents, and when we butted up against oceans built boats and set off across the water. It’s no wonder that we get antsy when the days become short and the nights cold. It’s our ancient selves whispering, “Go south, fool!”

Of course we’re not the only ones to hear those whispers. As early as August monarch butterflies begin their epic migration to the mountains of central Mexico. Among the best places to observe them is along Great Lakes beaches. Early and late in the day, when the wind is down, you can sit on the beach and watch monarchs flutter steadily southward, one every minute or so, their flight erratic but resolute.

By October warblers are passing through on their way to the Deep South, the Gulf Coast, and beyond. These are not the brightly colored warblers of spring. They wear  drab coats now, and it takes a practiced eye to know a pine warbler from a bay-breasted or a blackpoll.

Other birds are heading out, as well. I remember an unusually warm day in October in the western U.P. when I watched half-a-dozen hermit thrushes hopping across the ground in an aspen wood, flipping leaves in search of insects, moving constantly toward the south. I left the woods and turned onto a highway in my car. On the road ahead a flurry of leaves burst into the air and transformed into a flock of snow buntings, their white wings flashing in unison. During the drive home, the weather turned, and by the time I reached the Straits of Mackinac a harsh wind rattled sleet against my windshield. On both sides of the bridge were vast rafts of ducks on the water—redheads, according to my sources, and probably also some scaup, canvasbacks, and goldeneyes—so many that in their massed thousands they undulated on the waves like floating carpets the size of football fields.

When I was a kid I loved the migration season because it meant the summer people had made their way south and the lake was mine again. I went out in our aluminum rowboat and cast Mepps spinners into glass-calm bays, the surface reflecting the orange and yellow of hardwoods along the shore. At night, lying in bed, I would listen to the honking of geese as they passed overhead, bound for their winter grounds far to the south. It was the melancholy song of autumn, and it made my heart beat faster and my blood flow stronger. It still does. Some days I wouldn’t mind taking wing and following the geese south, but most days I’m quite content to stay here and see what comes next.