Copulation often occurs on the wing. The nest, which is built by both parents, is a cup of mud pellets lined with grass and feathers, built on ledges of wood or rock, located in caves, along cliffs, or in buildings. The female lays about 4 or 5 eggs and the incubation period lasts 15 to 17 days. Parents share many of the duties involved while eggs are in the incubation period. Young leave the nest after 18 to 23 days.
Barn swallows aggressively defend their territory from other birds.
They are often seen in large social groups sitting on telephone wires. Barn swallows have individual songs and they often sing as a chorus. Barn swallows build their nests in man made structures. Some common places include barns, under eaves, and in boat houses. They prefer open habitats of all types.