An extremely sociable North American bird that nests in colonies of several thousand pairs, the cliff swallow (Petrochelidon pyrrhonota) is primarily distinguished from other swallows by its orange rump, square tail and noticeably thicker head and neck. The forehead is white or brown, and both the crown of the head and the back are glossy blue-black. The sides and wings are brown, the breast is white and the throat, as well as a neck collar, are chestnut brown (4)(5).
Outside the breeding season, the cliff swallow’s plumage is slightly duller, the bill is faded black, and the legs and feet are dusky brown. The juvenile cliff swallow is similar to the adult, although the plumage is duller without any glossy colouration (4)(5).
With a short, wide bill forming a large gape, the cliff swallow is perfectly adapted for catching insects on the wing. It typically forages 50 metres or more above open ground, but also feeds over forest, water and towns. It also occasionally consumes seeds and gravel as this helps with digesting its hard-shelled insect prey. In large colonies, cliff swallows may work together to locate and feed on swarms of insects. Those individuals unable to find prey wait at the colony for a successful forager to return, before both birds travel to the insect swarm together (5).
The cliff swallow returns to colonies each breeding season. Breeding birds quickly pair up, with dominant birds establishing ownership of existing nests and subordinate pairs constructing new nests. The nest is built by both the male and female cliff swallow over a period of approximately seven days, although the male occasionally initiates construction before attracting a mate. Mud is collected with the bill and moulded onto an overhang above a vertical surface, with more mud slowly added until a round nest with a tunnel is created. The inside of the nest is lined with grass and wet mud that is pirated from unattended nests. One to six eggs are laid, at intervals of 24 hours. As an egg-laying parasite, this species may also lay some eggs in that of another cliff swallow’s nest so that they will be cared for by an unwitting, unrelated pair. The eggs are incubated by both birds for up to 19 days. Both the male and female feed the young for approximately three weeks, after which time the young fledge from the nest to join groups of other young in a crèche. Both adults continue to feed the young for at least another five days (5), primarily locating their young in the crèche by voice (3).
Breeding in North America and Central America, the cliff swallow migrates to South America before the winter, often visiting the Caribbean en route. It is an occasional visitor to Russia, the UK, Greenland, South Georgia and the South Sandwich Islands (1).
The cliff swallow forages in a variety of open habitats including grasslands, wetlands, arable land and broken forest, but avoid dense forest, desert and alpine areas. It requires water and a mud source for nest construction, with most colonies found on vertical cliff faces in canyons and river valleys, although bridges and buildings are also used (5). It is found up to elevations of around 3,000 metres (6).
An adaptable species that is extremely tolerant of human activity, the cliff swallow is increasing in range and possibly also number. Human development such as the construction of bridges and buildings has increased its breeding habitat. There are no known major threats to this species, although it is considered rare in some parts of its range, including north-eastern USA (1)(5).
Where attempts have been made to restore and conserve populations of this species, it has been found that controlling numbers of the house sparrow (Passer domesticus), which competes for nesting sites, greatly benefits the cliff swallow. To implement this, house sparrows may be trapped or shot, and old cliff swallow nests removed to prevent house sparrows reusing them. The removal of old nests also benefits the cliff sparrow by preventing the build up of parasites (5).
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