We caught a nest switch on tape; give it a listen. First, you'll hear the male singing (according to one of our bird biologists, the males "have an incessant drive to defend their space," so they often sing even while they're on the nest). Then, the female shows up with a buzzy trill, alerting the male that it's her turn. The male makes a few chips as he takes off followed by the fluttering wing beats of the female as she flies in to settle on the eggs.
