- 4.7–5.5 in
- 9.8–11.4 in
- 0.4–0.7 oz
- Sand Martin (British)
- Hirondelle de rivage (French)
- Golondrina ribereña, Golondrina Barranquera (Spanish)
- A Bank Swallow colony may range from 10 nests to nearly 2,000.
- The male Bank Swallow often pursues females other than its mate at the colony and attempts to mate with them. The male is most likely to chase a female in her fertile period.
- The oldest recorded Bank Swallow was at least 8 years old, when it was recaptured and rereleased during a banding operation in Wisconsin.
Bank Swallows live in low areas along rivers, streams, ocean coasts, or 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, more and more often these swallows populate human-made sites, such as sand and gravel quarries or road cuts.
Bank Swallows almost exclusively eat flying or jumping insects, such as bees, wasps, ants, butterflies or moths. The swallows catch insects while flying, usually at a height of 50 ft above water or open ground. Bank Swallows only occasionally taking insects from the ground or from the surface of water. They can feed singly or in large groups.
- Clutch Size
- 2–6 eggs
- Number of Broods
- 1-2 broods
- Egg Length
- 0.6–0.7 in
- Egg Width
- 0.4–0.6 in
- Incubation Period
- 13–16 days
- Nestling Period
- 18–24 days
- Egg Description
- Condition at Hatching
- Naked with scant gray down, weighing <0.1 ounce.
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 are perpendicular to the ground level and, when finished, are dug 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.
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 room for vertical 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.
Bank Swallows fly with shallow, fluttery wingbeats, typically gliding for less than 2 seconds at a time. Their flight style is less twisty than Barn Swallows but more direct than Northern Rough-winged or Tree Swallows. Bank Swallows are extremely social birds and are seldom alone when outside the nest. Because they nest in such proximity, they have developed many complex social behaviors. Bank Swallows huddle with other Bank Swallows, and even other swallow species, in extreme cold. It is common for Bank Swallows to fight for nests, mates, or nest materials by grappling. These birds land only rarely, though they will sidle across a telephone line or branch with a sideways walk.
North American Bank Swallow numbers declined by over 5% per year from 1966 to 2014, resulting in a cumulative decline of 94%, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 19 million with 22% spending some part of the year in the U.S., 8% in Canada, and most of the American population migrating through or wintering in Mexico. They rate a 10 out of 20 on the Continental Concern Score and the 2014 State of the Birds Report listed them as a Common Bird in Steep Decline. Bank Swallows are a state threatened species in California and a sensitive species in Oregon. Threats to Bank Swallows typically 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.