These gorgeous little cliff swallows were nesting in the rafters near the Anthropology Museum at Ghost Ranch, New Mexico yesterday. Cliff swallows (Petrochelidon pyrrhonota) are a friendly, brave little passeriforme that builds gourd-shaped nests from mud and straw. They tuck them up under cliffs, bridges and the edges of buildings. These two let me get within a meter of them.
American Cliff Swallows breed in large colonies. They build conical mud nests and lay 3-6 eggs. The natural nest sites are on cliffs, preferably beneath overhangs, but as with the Eurasian House Martin, man-made
structures are now the principal locations for breeding. Female American Cliff Swallows are known to lay eggs in and move previously laid eggs into the nests of other birds within the colony.This species has always been plentiful in the west of North America, where there are many natural sites, but the abundance in the east has varied.
European settlement provided many new nest sites on buildings, but the population declined in the late nineteenth and early twentieth centuries as the supply of unpainted barns declined. There has been a subsequent revival as dams and bridges have provided suitable sites.
The Cornell Lab of Ornithology has, of course, more great stuff on the Cliff Swallows including some good range maps:
When a Cliff Swallow has had a hard time finding food, it will watch its neighbors in the nesting colony and follow one to food when it leaves. Although sharing of information about food at the colony seems unintentional, when a swallow finds food away from the colony during poor weather conditions it may give a specific call that alerts other Cliff Swallows that food is available. By alerting other swallows to a large insect swarm an individual may ensure that the swarm is tracked and that it can follow the swarm effectively.