Bank swallows are smallish swallows with grayish-brown plumage on the head, back, wings, and tail. The flight feathers of the wings and tail have a slightly darker plumage color and there is a brown band that stretches across the breast. The chin, throat, belly, and undertail coverts are white. Juveniles may have buffy or whitish upperparts and a pink wash to the throat. Their tails are slightly notched. (Garrison, 1999)
Bank swallows can be confused with other, small brownish swallows. In North America this includes northern rough-winged swallows, which lack the breast band, and juvenile tree swallows, which are larger and differ in some plumage characteristics. Bank swallows may also be distinguished by their voice and their flight pattern: they hold their wings at a sharp angle in flight and use quick, flicking wing beats.
Bank swallows, or sand martins as they are known in Europe and Asia, are one of the few small perching birds that are found throughout most of the world. They migrate between breeding and wintering ranges. In the summer, breeding season they are found where suitable nesting areas are (see Habitat). In the Americas, bank swallows breed throughout much of Alaska and Canada to the maritime provinces and south to the mid-Atlantic United States, throughout much of the Appalachian chain, along the Ohio River Valley to Missouri, west throughout much of Kansas, along the Rocky Mountain Chain into New Mexico, and in the mountainous regions of Utah, Nevada, and northeastern California. They also breed along the Rio Grande river in Texas and northern Mexico. In winter, American populations migrate to South America and along the western coastal slopes of Mexico. In Europe and Asia they summer in the north from the British Isles east to Siberia and south to north Africa, the Middle East, and southeastern China. They winter in the Arabian Peninsula and throughout Africa and Madagascar.
Their scientific name, Riparia riparia, means "river bank river bank" and refers to the preferred breeding habitat of bank swallows. They nest in small to large colonies in soft banks or bluffs along rivers, streams, and coastal areas. They prefer the eroding banks of slow, winding rivers and streams. They also use sandy coastal bluffs or cliffs. Man-made habitats are now also used, including gravel pits, quarries, and road cuts. They are found from sea level to 2100 meters elevation, but most are found in lowland river valleys and coastal areas. Important foraging habitats include wetlands, large bodies of water, grasslands, agricultural areas, and open woodlands. Bank swallows mainly migrate along large bodies of open water, such as marshes, coastal areas, estuaries, and large rivers. In winter they are seen mainly in open habitats with large bodies of water and grasslands, savannas, or agricultural areas.
Bank swallows are monogamous and defend their nesting site together. Males begin to excavate burrows when they arrive on their breeding grounds. Once the nest burrow is about 30 cm long, they will begin to sit in the entrance and sing to attract females. They will also perform flight displays outside of the burrow entrance to attract females. The pair bond is formed as a female begins to sing in response to the male and perch near the burrow. Males and females will sleep together in the nest burrow. However, both sexes will occasionally try to mate with birds that are not their mates.
Once a mated pair is formed at a burrow, females begin building a nest in the burrow. Nests are lined with grass, feathers, and other fine materials. Females begin to lay eggs as early as April and into July. Most pairs attempt only 1 clutch per year, unless their first clutch is destroyed early in the nesting season. Females lay from 1 to 9, but usually 4 to 5, white eggs every day until the full clutch size is reached. Females begin incubating the clutch 1 to 2 days before all eggs are laid. Incubation takes 13 to 16 days and eggs hatch over the course of several days. Fledging occurs at around 20 days after hatching and parents continue to feed their young for 3 to 5 days after fledging. Once they become independent, young bank swallows gather in flocks of juveniles and adults. They are forced away from the burrow they were raised in by their parents, but often gather in small groups at other burrows to rest. Males and females can breed in their first year after hatching.
Male and female bank swallows share in incubating young, although females do most incubation. Both parents sleep in the nest burrow at night. Young are naked and helpless at hatching and parents brood them for 7 to 10 days. Both parents feed the young and help to protect them from predators until they are 23 to 25 days old, a few days after they have left the nest burrow.
About 60% of bank swallows may die each year, with higher death rates in young bank swallows. Two bank swallows lived to 9 years old in the wild.
Bank swallows are gregarious, living and breeding in colonies. Bank swallows that live in larger colonies are more successful at detecting and defending against predators, but they also have more parasites. Bank swallows are always very social, they preen each other, sunbathe, and roost in large groups. Bank swallows migrate fairly long distances, often in flocks with other swallows. They arrive on their breeding grounds in early spring and leave in late summer. On their winter range, bank swallow populations may range widely in search of food. They forage from early in the morning through dusk. Like most swallows, bank swallows are fast and agile in flight. Their flight is described as "fluttery," with rapid wing beats and short glides. Their wings are held bent in flight, unlike most other swallows. They will forcefully hit, and then bounce off of, the surface of water to drink, gather nesting material, grab an insect, or bathe themselves. Bank swallows are ungainly on the ground and are mainly seen perching or in flight.
Nesting pairs defend only their nest burrow and the area immediately around the burrow. Home range sizes are not reported. (Garrison, 1999)
Young bank swallows use a food-begging call and a signature call to their parents at the nest. Parents recognize the calls of their own offspring. Parents respond with a feeding call when they return to the nest to feed their young, the feeding call is described as a set of sweet notes. Contact calls are the most commonly used and are described as a raspy "tschr." Males also sing to advertise territories and attract females for mating. Males can sing at the nest and in flight. Songs sound like "cher-che-che-che," repeating until it sounds as if they are chattering. Bank swallows also use warning and alarm calls when they observe predators. Warning calls are given to colony-mates while alarm calls are directed at predators when they are being mobbed.
Males also perform display flights to attract females. (Garrison, 1999)
Bank swallows eat almost exclusively insects that they catch in flight. They forage from dawn to dusk over bodies of water or large areas of short-growing vegetation, such as meadows, agricultural fields, or wetlands. They sometimes forage over forest canopies. Bank swallows drink in flight as well, by skimming the water surface with their lower bill. In one study of stomach contents, bank swallows ate 99.8% insects, with approximately 33.5% ants, bees, and wasps, 26.6% flies, 17.9% beetles, 10.5% mayflies, 8% bugs, 2.1% dragonflies, and 1.2% moths and butterflies.
Bank swallows that live in larger colonies are better at detecting and defending against predators. They cooperate to mob predators that threaten their colony. Most predation is on nestlings and eggs in burrows. Snakes are important predators of nestlings, including gopher snakes (Pituophis melanoleucus) and black rat snakes (Pantherophis obsoletus). American kestrels (Falco sparverius) attempt to take flying adults and fledglings. Bank swallows have been observed deterring predation by blue jays (Cyanocitta cristata) when they mob them.
Bank swallows are important predators of flying insects, especially where they concentrate around breeding colonies. European starlings and house sparrows may take over their burrows. Other sand and bank burrowing birds, such as kingfishers, barn owls, northern rough-winged swallows, and cliff swallows are tolerated by bank swallows. (Garrison, 1999)
Bank swallows that live in larger colonies suffer higher rates of flea infestation and nestlings with fleas had lower body masses than nestlings without fleas.
There are no known adverse effects of bank swallows on humans.
Through their predation on flying insects, bank swallows can help to control populations of pest insects, such as mosquitoes and agricultural pests. (Garrison, 1999)
Bank swallows are widespread and population sizes are large. The IUCN considers them "least concern." However, local populations are impacted by loss of nesting habitat. In California they are listed as threatened, they are considered sensitive in Oregon, and a species of special concern in Kentucky. Bank swallows are fairly tolerant of human activities and will even nest in active quarries. (BirdLife International 2008, 2008; Garrison, 1999)
Tanya Dewey (author), Animal Diversity Web.
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