Look for their large nesting colonies on cliffs as well as on buildings and under bridges. Polytypic. Length 5.5".
Adult: square tail; orangish buff rump; dark cap extending below eye; chestnut cheeks, sides of neck, and throat; bluish black on lower throat; cream to buffy forehead patch. Underparts, including flanks, whitish. Juvenile: similar to adult, but entire head usually dark brownish black, sometimes with small pale grayish, whitish, or rusty forehead patch. Rump paler buff. Chin and upper throat pattern quite variable, some mixed with white, full black, gray, or cinnamon. Flight: short triangular wings and square tail. Whitish underparts and paler underwings contrast with dark head and throat. Hybrid: very rare; hybrids with the barn swallow and tree swallow (once) known. Cave swallow hybrids possible but not confirmed.
Considerable intergradation between 4 recognized subspecies. Western (hypopolia) similar to nominate Eastern (pyrrhonota) subspecies, but larger, with larger, paler forehead, whiter breast, grayer flanks, paler rump, more rufescent underparts. Two southwestern subspecies, tachina and melanogaster, are smaller, show darker cinnamon to chestnut foreheads.
Call: a subdued squeaky twittering given in flight and near nest.
Status and Distribution
Locally common. Breeding: various habitats, including grasslands, towns, open forest, and river edges wherever there are cliff faces or escarpments for nesting. Small to large colonies, on cliff faces and on man-made structures (sometimes with barn swallows), rarely at cave entrances. A gourd-shaped structure built entirely of mud and saliva; 1–6 eggs (April–June). Migration: always via Central America. Departs winter range in early February. Arrives in southern California in early February, Arizona in early March, Illinois in early April, and Alaska in mid-May. Departs after nestlings fledge, sometimes as early as late June. Peak is August–early September, earlier in Southwest (July–early August). May linger to early November in East. Winter: grasslands, agricultural areas, near towns, and in marshes. South America, from southern Brazil south to south-central Argentina. Vagrant: casual in Barbados in winter. Accidental to Wrangel Island, Siberia, southern Greenland, and United Kingdom.
Has expanded its range into the Great Plains and eastern North America in the past 150 years.
—From the National Geographic book Complete Birds of North America, 2006