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Formerly restricted to canyons, foothills, and river valleys with natural cliff faces and overhangs, Cliff Swallows have spread into a wide variety of habitats by nesting on buildings, bridges, and other human-made structures.
Cliff Swallow nests have been used for breeding by Say’s Phoebes, Chestnut-backed Chickadees (Parus rufescens), Plain Titmice (P. inornatus), House Wrens (Troglodytes aedon), Eastern Bluebirds (Sialia sialis), House Sparrows, and House Finches (Carpodacus mexicanus) (Mayhew 1958, Weeks 1995, CRB, MBB); all but the phoebe may usurp active ...
Although the Cliff Swallow can nest solitarily, it usually nests in colonies. Colonies tend to be small in the East, but further west they can number up to 3,700 nests in one spot. Within a Cliff Swallow colony some swallows lay eggs in another swallow's nest.
Cliff swallows decide upon arrival at their nesting site whether they will fix a nest from the previous season or build a new nest. [ 2 ] [ 4 ] Building a new nest may have the benefit of lower parasite numbers, but it is very energy expensive and time-consuming.
Cliff swallows may spread plant seeds during nesting and migration. Birds will compete for nests with barn swallows (Hirundo rustica) and convert them to the cliff swallow style nest. Cliff swallows are also brood parasites within their colonies.
Cliff swallows decide upon arrival at their nesting site whether they will fix a nest from the previous season or build a new nest. Building a new nest may have the benefit of lower parasite numbers, but it is very energy expensive and time-consuming.
Cliff Swallows are extremely colonial, and larger colonies can reach up to thousands of pairs, with nesting activity highly synchronized within larger colonies. Compared to western colonies, those in the Northeast are smaller, rarely exceeding 100 pairs.
