If you think our Birdorable birds are cute as adults, what about when they are babies? Below are some baby photos (shared via Flickr Creative Commons) of the Barn Swallow. Barn Swallows build a nest of mud, often on a man-made structure. Both the male and female build the nest, which is fortified with blades of grass. The nest is then lined with softer material, like grass and feathers. The baby birds hatch after about two weeks of incubation, and fledge from the nest after another three weeks or so.