Hey, Stranger

IN MONTANA, AS IN MOST OF the Lower 48, American Robins are present year-round. So I had long assumed that the cheerful songbird hopping around my yard in the fall had nested nearby that summer. Imagine my surprise, then, to learn it may have spent those months a thousand miles or more to the north. Where these common birds go, and what drives their decision to migrate long or short distances—or simply stay put—are mysteries that scientists are just starting to solve.

“They’re a truly cosmopolitan bird,”