Bobbing down, she presses her breast into the cup to shape it. Finally she lines the cup with soft grasses, a gentle die for her eggs. As anyone knows who has watched a nest of robin hatchlings outside their bedroom window, baby birds are noisy, fascinating, and able to get their parents dancing with their plaintive cheeps. Songbird young are the size of the adult by the time they fledge. But they're not yet ready to be grownups.
Hummingbirds build tiny nests the size of Japanese sake cups, wedged in the fork of a branch.
They line their nests with spider silk-satin sheets for the crib. But not all parents make a soft and fancy nest for their young. Killdeer scrape together a few pebbles or may lay their eggs on a bare patch of sand, or atop a gravel roof. Kestrels, though their young are more dependent than killdeer, use cavities but lay their eggs on the bare surface. Mammals are not as dependent on holes in trees as are the many cavity-nesting birds, which include bluebirds, chickadees, house sparrows, nuthatches, tree swallows, even wood ducks.