American cliff swallows (Petrochelidon pyrrhonota) are robust migratory birds of the passerine family of Hirundinidae, the most famous colony of which now lodges in San Bernardino County in the spring and summer during the birds’ breeding season.
This bird averages 5.1 inches long, 0.74 ounces in weight with an impressive 13.5 inch wingspan, and a tiny bill. The adult cliff swallow has an iridescent blue back and crown, brown wings and tail, and buff rump. The nape and forehead are white. The underparts are white except for a red face. The tail is square-ended.
Young birds are essentially brown above and whitish below, except for the buff rump and dark face. The only confusion species is the closely related cave swallow, which is richer in color and has a cinnamon rump and forehead.
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.
Like all swallows and martins, cliff swallows subsist primarily on a diet of insects which are caught in flight, particularly beetles (including June beetles and adult weevils), true bugs, flies, winged ants, bees, and wasps. They also eat grasshoppers, mayflies, lacewings, and various other insects, plus some spiders. They often forage in flocks, and may feed low over the water or very high over other terrain. In bad weather, they may feed on the ground and occasionally eat berries.
Females typically lay three to six white to pale pinkish eggs, spotted with brown. Incubation is by both parents, which lasts 14 to 16 days. Both parents bring food for nestlings. The young leave the nest about 21 to 23 days after hatching.
American cliff swallows breed in large colonies. They build conical mud nests and lay three to six 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.
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 most famous colony of cliff swallows are those that nested in droves on the side of Mission San Juan Capistrano, beginning perhaps as early as the 18th Century. The mission’s location near two rivers made it an ideal location for the swallows to nest, as there was a constant supply of the insects on which they feed, and the young birds are well-protected inside the ruins of the old stone church. According to legend, the birds, which returned to the San Juan Capistrano area on or around March 19 for centuries and also frequent the Mission San Carlos Borromeo de Carmelo, first took refuge at the mission when an irate innkeeper began destroying their mud nests. Because extensive repairing and shoring up of the church’s wall disturbed the nests some two decades ago, the colony of swallows, which ventures 6,000 miles to Villa Ventana and Goya, Argentina every year with the approaching winter, now nests upon returning to California in the spring in the in the eaves of the Vellano Country Club in Chino Hills The swallows have also been spotted nesting in the eaves of the Orange Terrace Library and Community Center in Riverside.
Smaller colonies are present elsewhere in San Berbardino County, including in the Mojave desert north of Barstow on the grounds of Fort Irwin