Bank Swallow Life History

Habitat

Bank Swallows live in low areas along rivers, streams, ocean coasts, and reservoirs. Their territories usually include vertical cliffs or banks where they nest in colonies of 10 to 2,000 nests. Though in the past Bank Swallows were most commonly found around natural bluffs or eroding streamside banks, they now often nest in human-made sites, such as sand and gravel quarries or road cuts. They forage in open areas and avoid places with tree cover.

Food

Bank Swallows almost exclusively eat flying or jumping insects, such as bees, wasps, ants, butterflies, and moths. The swallows catch insects while flying, often as high as 50 feet above water or open ground. Bank Swallows only occasionally take insects from the ground or from the surface of water. They feed singly as well as in large groups.

Nesting

Nest Placement

Bank Swallows build nests, often in large colonies, in vertical banks and bluffs. These colonies are usually made in fairly loose soils that are easy for the birds to burrow into, and are located near large bodies of water so that there is ample airspace for flying. Each individual Bank Swallow chooses first a colony, according to its location, and then a nest site within the colony area. The male begins to dig a burrow into the bank before he has a mate; the female then hovers in front of burrows to choose a mate and his nest site. The nests are usually located mostly in the upper third of the bank to avoid ground predators.

Nest Description

Male Bank Swallows use their small, conical bills as well as their feet and wings to dig burrows that will lead to a nest chamber. The burrows, when finished, extend about 25 inches into the side of the bank. The male enlarges the tunnel upward and to both sides to form the nest chamber, where the temperatures are more constant than outside the burrow. The female then builds most of the nest itself, constructing a flat mat of straw, grasses, leaves, or rootlets that she has torn from the exposed bank. The nest mat is approximately 1 inch thick and 5 inches in diameter.

Nesting Facts

Behavior

Bank Swallows, like many of their close relatives in the swallow family, are consummate aerial predators, deft in their pursuit of flying insects. Wingbeats are generally shallow and fluttery, with brief glides. They are less twisty in flight than Barn Swallows and more direct than Rough-winged or Tree Swallows. Bank Swallows are extremely social birds, and are seldom alone away from the nest, either in the company of other Bank Swallows or among other species of swallows, especially in migration. Bank Swallows huddle with other swallows in periods of extreme cold. During the nesting season, males begin to dig a burrow into the bank before they have mates; then they perform territorial circle flights around the burrow entrance while singing, attempting to attract females to their burrow. An interested female hovers in front of the burrow to choose a mate and his nest site. Males defend the burrow and the immediate surroundings from other males, but abandons the burrow if it does not attract a female. Pairs remain together for the breeding season, but the members of the pair often mate with other individuals in the colony.

Conservation

Bank Swallows are listed by Partners in Flight as a Common Bird in Steep Decline. Their North American numbers have crashed by an estimated 89% since 1970. The global breeding population is estimated at 26 million. They rate an 11 out of 20 on the Continental Concern Score, reflecting the fact that they are still widespread and fairly numerous, despite these extreme recent losses. While Bank Swallows are generally quite tolerant of human disturbance, threats can come from changes to its nesting habitat of vertical sand or mud banks and bluffs. Erosion control, flood control, and road building projects that remove these banks or make them less steep make them unsuitable for Bank Swallows. Construction projects that involve high mounds of gravel or dirt can attract nesting Bank Swallows—though they can also destroy nests if the material is removed before the nesting season ends. Bank Swallows are aerial insectivores—a group that as a whole has recently undergone steep, unexplained declines.

Credits

Garrison, Barrett A. (1999). Bank Swallow (Riparia riparia), version 2.0. 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 (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxent Wildlife Research Center (2014b). Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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