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Cliff Swallows are colonial — that is, they nest in colonies, sometimes numbering in the thousands of birds. In many ways the members of a colony appear to display remarkable social cohesiveness. They work together to mob predators and will even learn from each other where the good food sources are. But if you look closely at a Cliff Swallow colony, you’ll see that this seemingly cooperative community also harbors its share of dastardly misbehavior.
In every colony there are a few swallows (you might call them bad eggs) that parasitize their neighbors. They do this not by sucking other swallows’ blood or stealing food, but by putting their eggs in nests other than their own. Sometimes the sneaky swallow will even toss out one of the nest owner’s eggs before laying her egg in its place! This behavior is known as brood parasitism. The extra eggs go undetected, and the surrogate parents end up doing the work of raising the slacker’s young.
These parasitic egg-laying visits are clandestine and quick, but some Cliff Swallows have been spotted launching an even faster, more remarkable sneak attack: carrying eggs in their very small beaks (adapted for catching tiny insects on the wing) and quickly dropping them into a neighbor’s nest. Incoming!
Cliff Swallow Petrochelidon pyrrhonota (Hirundo pyrrhonota
Family: Hirundinidae, Swallows view all from this family
Description 5-6″ (13-15 cm). Sparrow-sized. A stocky, square-tailed swallow with pale buff rump. Upperparts dull steel-blue; underparts buff-white; throat dark chestnut; forehead white. Southwestern birds have chestnut foreheads. Cave Swallow of Texas and Southwest is similar but smaller, with darker rump and pale buff throat.
Habitat Open country near buildings or cliffs; lakeshores and marshes on migration.
Nesting 4-6 white eggs in a gourd-shaped structure of mud lined with feathers and placed on a sheltered cliff face or under eaves. Nests in colonies.
Range Breeds from Alaska, Ontario, and Nova Scotia southward through most of United States except Southeast. Winters in tropics.
Voice Constant squeaky chattering and twittering.
Discussion As its name implies, this swallow originally nested on cliffs. The introduction of House Sparrows was a disaster for these birds, since the sparrows usurp their nests and often cause the swallows to abandon a colony. Long, cold, rainy spells while the young are in the nest also cause widespread mortality since the adults are unable to obtain enough insects. In California they often return in early spring to ancestral colonial breeding sites. If it turns chilly, however, they will abandon the area until weather and feeding patterns are more favorable, and return “on schedule” for their publicized arrival on March 19 at Mission San Juan Capistrano.
