Heinrich is sparked one early spring day by a question: Why does a pair of swallows in a nest-box close to his Maine cabin show an unvarying preference for white feathers – not easily available nearby – as nest lining? He notices, too, the extreme aggressiveness of “his” swallows toward some other swallows of their own kind. And he wonders, given swallows’ reputation for feistiness, at the extraordinary tameness and close contact he experiences with his nesting birds.