The cave swallow (Petrochelidon fulva ) is a medium-sized, squarish-tailed swallow belonging to the same genus as the more familiar and widespread cliff swallow of North America. The cave swallow, also native to the Americas, nests and roosts primarily in caves and sinkholes.
Cave swallows are found in Mexico and the Greater Antilles, with fall and winter vagrants reaching the east and Gulf Coasts of the U.S. Breeding colonies occur in south-eastern New Mexico, Texas, Florida, the Greater Antilles, portions of southern Mexico, and along the west coast of South America. Five subspecies are currently recognized according to Birds of North America, three occurring in North America and two in South America.
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starts withThe cave swallow measures 12 to 14 cm in length and weighs 19 g on average. The largest of the five subspecies, P. f. pallida, has an average wing length between 107.0 and 112.3 mm; the smallest subspecies, P. f. aequatorialis, has an average wing length between 93.0 and 93.5 mm. Differences between the sexes are minimal, both are similar in size and weight and are difficult to distinguish from their plumage. It has grey-blue upperparts and brown-tangerine forefront and throat.
During the breeding season, P. f. fulva, P. f. pallida, and P. f. citata, the North American subspecies of the cave swallow, will usually nest in a caves, sinkholes, and sometimes in man-made structures offering similar habitat, such as highway culverts. P. f. aequatorialis and P. f. rufocollaris, the South American subspecies, prefer to nest in open areas such as on cliff faces and the sides of buildings.
All subspecies of the cave swallow forage for insects over open areas and water nearby their roosting sites. Their spring and fall migrations are poorly known; however, P. f. citata, P. f. aequatorialis and P. f. rufocollaris are considered resident species and winter in their breeding range.
P. f. pallida is found farther west in the south-western United States and into north-eastern Mexico. P. f. citata has the southernmost range of the North American subspecies and is found on the Yucatán Peninsula of Mexico. P. f. aequatorialis is found in Ecuador, and it is speculated that it may extend its range into Peru. P. f. rufocollaris occurs in north-western Peru.
Breeding is known to occur in Mexico, south-eastern New Mexico, southern Florida, Greater Antilles and in areas of Texas. The South American populations, as well as most Mexican and Caribbean populations, are considered resident populations which breed and overwinter in the same geographic range. The New Mexico and other northern populations migrate south; however, it is not known where they migrate to or which migration routes they take. Cave swallows have been observed to overwinter in southern Texas since at least the 1980s.
As previously mentioned, North American subspecies of cave swallows roost and nest primarily in caves and sinkholes while the South American subspecies prefer open spaces such as cliff-faces and the sides of buildings. Breeding occurs between April and August. North American subspecies are currently undergoing a human-facilitated range expansion due to the increased availability of alternative nesting sites. These include highway culverts and bridges. In Texas alone cave swallows have increased their breeding range 898% between 1957 and 1999, with populations increasing at a rate of about 10.8% each year.
Cave swallows are open-cup nesters, meaning they build a nest shaped like a cup with the top left open for them to fly in and out. The nests are made of mud and bat guano and can be reused for multiple breeding seasons. Old barn swallow nests are also utilized by cave swallows, which will modify them to suit their needs. Barn swallows and cave swallows are observed to co-exist at some nesting sites, making old barn swallow nests easily available to the cave swallow. Cave swallows are social and prefer to nest in variably sized colonies. They are even observed to occasionally share nest sites with other species of swallows, such as barn swallows. This occurs particularly often in north central Mexico and increasingly in the United States with the increased use of highway culverts as nesting sites. Some concerns have been raised about the potential for, and instances of, interbreeding between the two species and the viability of the hybrids.
While the use of human-made nesting sites has allowed the cave swallow to greatly increase its range across North America, it may come with its own risks. Culvert and bridge nesting sites have an increased risk of flooding the nest area, a more variable thermal regime during the breeding season, an increased instance of sharing the colony site with other species, an increased risk of nest predation, and fewer available nesting materials. Caves and sinkholes, however, are not at great risk of flooding, have a less variable thermal regime, lower instance of sharing the site with other species, lower risk of predation, and easily available nesting materials. All this being said, cave swallows nesting at the culvert site laid more eggs, had more eggs hatch, and had more nestlings survive than those nesting at Dunbar Cave in 1974, which could explain why the population is growing so rapidly while using a riskier nest site.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...