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. It is a welcome insect predator on most farms. Some humans feel that swallow nests are a nuisance and unsightly simply because they are attached to man made buildings and structures.