Swallows are often associated with grasslands and agricultural fields, but they often forage over water as well. In many cases, the loss of natural nesting sites has led these species to use human-made or human-altered structures for nesting.
Bank swallows commonly nest in the naturally eroding banks along rivers, streams and ocean coasts. As humans stabilize more of these banks, this species has adapted to using gravel and sand quarries, road banks and reservoirs. The male will use his bill, feet and wings to dig a burrow in the bank that leads to a nest chamber. The female then builds the nest with straw, grass, leaves and roots from the bank.
Barn swallow (pictured)
Barn swallows build cup-shaped nests out of mud, locating them in barns and sheds or under the eaves of buildings and bridges. They frequently reuse nests from past years — not surprising, since a pair of barn swallows must make over 1,000 trips to build a new nest, bringing back a mouthful of mud each time. Historically barn swallows used caves and cliff faces for nesting, however they quickly shifted to take advantage of human-made habitat. There are early records of barn swallows using First Nations wooden dwellings, and the diversity of potential nest sites and foraging habitat only grew following European settlement. Nowadays barn swallows nest almost exclusively in human-made structures.
Cliffs are the natural nesting habitats for the cliff swallow, but they will also nest under structures like buildings and bridges. In recent years, cliff swallows have also begun to opportunistically use barns, where they can out-compete barn swallows for the best nesting sites due to their larger size. They build gourd-shaped nests of mud and will even build on top of old barn swallow nests.
Tree swallows build a cup-shaped nest of grass or pine needles in tree cavities. Tree swallows have also readily adapted to using nest boxes when natural sites are not available. Tree swallows may nest near one another, especially if several nest boxes are located close together, but they do not form colonies like other swallow species.