Cliff Swallows are monogamous. Although they can nest solitarily, they are very social birds and tend to nest in colonies that can include up to 3,500 nests. These colonies help them detect predators and increasing their chances of escaping a predator. Both males and females contribute to nest building by sticking mud balls to the side of a wall, such as a barn, cliff, or the underside of bridges. When completed, these nests are jug-like in appearance; hence the nests are referred to as “mud-jugs.” The inside of the nests are lined with grasses and feathers.

Female Cliff Swallows have been known to lay their eggs in another colony member’s nest. Sometimes they may even carry an egg from their own nest and place it in a different nest. Females can lay anywhere from 1 to 6 eggs, which are incubated for 14 to 16 days. These eggs are pale pink or white in color and are marked with brown. Both the male and the female incubate the eggs and take turns feeding them when they hatch. The young fledge after 3 weeks. When they leave the nest, the young can gather in large groups called “crèches”. Parents can recognize their young in these crèches primarily by their voice and facial markings.

Cliff Swallows are commonly found near farmlands and wetlands during the summer, and are occasionally seen at Iroquois National Wildlife Refuge and Allegany State Park.