In Michigan, Barn Swallows come up from South America in the spring to breed. They are very adaptable birds and can nest anywhere with open areas for foraging, a water source, and a sheltered ledge. Barn Swallows once nested in caves throughout North America, but now build their nests almost exclusively on human-made structures.
Breeding pairs form each spring and can produce 2 clutches per season from May until August. Both parents incubate about 5 eggs for about two weeks, feed their nestlings for about 20 days and continue to feed them for about 2 weeks after they have fledged.
Barn swallows are quite effective in reducing insect pest populations. While in the nest, barn swallow parents may feed their nestlings up to 400 times per day. Flies, grasshoppers, crickets, dragonflies, beetles, moths and other flying insects make up 99 % of their diet. They catch most of their prey while in flight, and are able to feed their young at the nest while flying.
The survival of the Barn Swallows and their relationship with humans may have been helped by superstition that any damage to a Barn Swallow's nest leads to cows with no milk and to hens without eggs.