Bank Swallow

This highly colonial species typically nests in eroded banks along medium to large rivers, although it will also use similar banks in excavated gravel pits and piles of dirt at construction sites. Preferred nesting substrate consists largely of sand, and colonies are typically located near the top of banks in near vertical portions. Banks can range in height from two to over twenty feet, but colonies are most often found in those in the 6–10-foot range. Nests are placed at the end of two-foot-long burrows that are dug by the birds.

Bank Swallow colonies along rivers are at the mercy of both gravity and the flow of water, both of which cause additional erosion that can wipe colonies from the face of a bank. As a result, these swallows don’t show strong site faithfulness, and regularly move if their colony is destroyed in this manner. The same applies to disturbance at man-made nesting sites such as gravel pits. If a colony is lost early in the nesting season it may be able relocate quickly and still successfully produce young that year.

Unfortunately, the Bank Swallow is one of the most rapidly declining breeding birds of New Hampshire. During the Breeding Bird Atlas in the 1980s it was found statewide, but now occurs primarily in the major river valleys. Most colonies are along the Connecticut, with smaller numbers on the upper Merrimack and Saco. The species also uses gravel bits in these areas, and these are apparently the only sites now used in southeastern New Hampshire.

Anything that affects the long-term survival of nesting banks is a potential threat to this species. The most direct threat is efforts to reduce riverside erosion by channelizing or stabilizing banks, often to protect adjacent land from falling into rivers. This threat is multifaceted, since it not only eliminates an existing bank but has the potential to alter erosional patterns in nearby stretches of the same river, thus altering future habitat elsewhere. At the same time, climate change is leading to more variable precipitation patterns, and resultant flooding can also eliminate habitat. Climate change may affect Bank Swallows during the winter as well. Studies of European populations have shown lower overwinter survival in years of drought in southern Africa, and it’s reasonable to assume that a similar relationship applies to our swallows, which winter in South America.