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. They now live in grasslands, towns, broken forest, and river edges, but avoid heavy forest and deserts. In the south-central and northeastern states they are rare and localized breeders. Most colony sites are close to a water source, open fields or pastures for foraging, and a source of mud for nest building. Cliff Swallows spend the winter in grasslands, farmland, marshes, and the outskirts of towns in southern South America.Back to top
Cliff Swallows eat flying insects all year round, foraging during the day in groups of 2 to more than 1,000 birds. They feed on the wing above grassy pastures, plowed fields, and other open areas, but also over floodplain forests, canyons, and towns—often taking advantage of thermal air currents that bring together dense swarms of insects. In cool or rainy weather when insects are scarcer and thermals weaker, they may also feed over lakes, ponds, and rivers. Cliff Swallow colonies serve as foraging information centers as parents make trips back and forth to feed nestlings: unsuccessful foragers follow their successful neighbors to food sources. Their diet consists of many types of flying insects (particularly swarming species), including bugs, flies, bees, wasp, ants, beetles, lacewings, mayflies, butterflies, moths, grasshoppers, crickets, dragonflies, and damselflies.Back to top
Each Cliff Swallow pair first chooses a colony, then takes over an existing nest or selects a space on the colony to build a new nest. Colonies may be located on cliffsides, caves, building eaves, bridges, highway culverts, dams, or large trees, and each nest is built at the juncture between a vertical wall and a horizontal overhang. The female spends more time than the male scoping out colony sites before they settle on one. An unmated male may choose a site on his own and later attract a mate.
Both sexes help build the nest, though the male may begin building before he attracts a mate. They gather mud in their bills along streambanks, lakesides, or puddles, usually near the colony but sometimes up to a few miles distant. They bring mud pellets back in their bills and mold them into place with a shaking motion. The finished nest is gourd shaped and contains 900–1,200 individual mud pellets. It measures about 8 inches long, 6 inches wide and 4.5 inches high, with walls 0.2–0.7 inches thick. The entrance, which is sometimes elongated into a tube, is about 1.7 inches high and 2 inches wide. The pair lines their nest with dried grass and continues patching it up with mud throughout the breeding season.
|Clutch Size:||1-6 eggs|
|Number of Broods:||1-2 broods|
|Egg Length:||0.7-0.9 in (1.8-2.4 cm)|
|Egg Width:||0.5-0.6 in (1.3-1.5 cm)|
|Incubation Period:||10-19 days|
|Nestling Period:||20-26 days|
|Egg Description:||White, creamy, or pinkish, with brown speckles or blotches.|
|Condition at Hatching:||Helpless, with bare pink skin, weighing less than a tenth of an ounce each.|
Cliff Swallows are the most colonial swallow in the world, regularly forming colonies of 200–1,000 nests, with a maximum of 3,700 nests in one Nebraska site. They preen, feed, drink, and bathe in groups, and they continue sticking together in large flocks during migration and on their wintering grounds. Cliff Swallows sleep in trees for most of the year, but a breeding bird will start sleeping in the nest as soon as the structure is partially finished. They fight for nest sites by grappling in half-built nests or on the bare wall. Fighting birds sometimes fall into the water and manage to row with their wings to reach the shore. Nest owners defend their completed nests by sitting in the entrances, puffing up their head and neck feathers to look larger, and lunging at intruders. Each bird has one mate with whom it raises young, but the pair does not associate away from the nest, and both members frequently mate outside the pair bond. Cliff Swallow predators include Sharp-shinned Hawks, American Kestrels, Prairie Falcons, Peregrine Falcons, Barn Owls, Great Horned Owls, Mississippi Kites, Black-billed Magpies, Loggerhead Shrikes, Common Grackles, Acorn Woodpeckers, Red-headed Woodpeckers, bull snakes, rat snakes, coachwhip snakes, rattlesnakes, fire ants, mink, and domestic cats.Back to top
Cliff Swallows are numerous, and their populations were relatively stable between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 83 million and rates them 6 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Swallow numbers probably increased dramatically beginning in the nineteenth century as they expanded into new breeding habitats such as bridges, buildings, and culverts. At the same time, their breeding has been impeded by the spread of invasive House Sparrows, which often take over their nests. In the northeastern United States, this caused Cliff Swallow numbers to drop during the 1900s. Other regions that have seen declines include the Pacific Northwest, coastal California, and the Great Lakes, although these have been balanced by increases in other parts of the continent. Management officials have successfully increased local Cliff Swallow populations by trapping House Sparrows at colony sites. The species has expanded in the southeastern United States in recent decades.Back to top
Brown, Charles R., Mary B. Brown, Peter Pyle and Michael A. Patten. (2017). Cliff Swallow (Petrochelidon pyrrhonota), version 3.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.
Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.