The 3 nestling Tree Swallows are peeking out to get some air on this hot day. They have inborn abilities to fly, which develop gradually as the young bodies grow. By the time the parents coax the nestlings out, the young will have been exercising their wings within the boxes for days. When they are physically ready for flight, the parents know and reduce their feeding trips into the box. Instead, the parents may perch on the door and hold out a morsel for one nestling, teasing it to come out and try its wings.
