The Sand Martin is interesting in that it is capable of sustained flight from the first time that it launches itself from its nest hole. This is necessary for a Sand Martin to survive as, traditionally, the nest hole was, and often still is, in a sheer cliff face, often above water. It gains this ability over a number of days by flapping its wings vigorously in the nest/hole to strengthen them, then pressing its primary wing feathers and tail hard down onto the nest/hole at an angle of 45 until it is able to support its body by these alone. When it is able to support its body by its wings and tail alone for more than a few seconds, then, instinctively, it will launch itself from the nest hole.
A small (4 ½ to 5 ½ inches) swallow, the Bank Swallow is most easily identified by its brown upperparts, white belly white throat, and dusty brown chest stripe separating the throat from the belly. This species may be separated from the similarly-patterned Northern Rough-winged Swallow (Stelgidopteryx serripennis) by that species’ larger size and brown chin. The Bank Swallow occurs across much of the world. In the Americas, this species breeds from Alaska and central Canada south locally to the Mid-Atlantic region in the east and northern Mexico in the West, wintering on the Pacific coast of Mexico and further south to central South America. In the Old World (where it is known as the Sand Martin), this species breeds across Eurasia from Siberia south to North Africa and the Indian subcontinent, wintering across tropical Africa and South Asia. Historically, Bank Swallows bred in a variety of habitats near water, frequently building their nests on cliffs along the banks of rivers. Today, this species often nests on man-made structures such as buildings and bridges. In winter, this species is likewise found in habitats near water, including lakes, rivers, marshes, and reservoirs. Bank Swallows exclusively eat flying insects. As is the case with most swallow species, it is possible to observe Bank Swallows feeding on insects while in flight. Birdwatchers in this species’ breeding range may want to pay special attention to bridges or the eaves of buildings, as a careful search of these structures may reveal a nesting colony. Bank Swallows are primarily active during the day.
The Sand Martins breeding in the Western Palearctic and wintering in the Western Sahel region of Africa are double-brooded, (1) or more definitively, multi-brooded (2,3). In one Study over an 18 year period at one site in Scotland at longitude 1W, the degree of multi-brooding was assessed.(4) The percentage of 1349 successful broods appearing in nest holes holding one brood during a season was 37%, nest holes holding two broods 62%, and nest holes holding three broods 1%. During the same study, male Sand Martins occupied a nest hole through the whole of the breeding season unless they died through predation or from other causes. The multi-brooding occurs when females whose mates are capable of provisioning a brood alone, are left to do so when the females start a new clutch with a new mate, thus improving their own productivity. (3,5.)
In a study in central Europe at longitude 21E (6) it was found that seasons when there were no second broods did not affect the population size in the following breeding season. However, in Britain (7) surviving juveniles from those fledging during June, July and August, covering the first and second brood periods, were found to contribute to the following years breeding population.
This multi-brooding behaviour is quite distinct from those Sand Martins breeding throughout most of the Holarctic region which are decidedly single brooded (8,9). It was found (10) that the breeding population in Britain fell by over 90% between 1968 and the mid 1980's when there were particularly severe droughts in the Western Sahel region. Such losses of population are caused by these Sahelian droughts (6,11,12,13,), and also by adverse weather, mainly torrential or prolonged precipitation during periods when the Sand Martins are provisioning young (Cowley14.). This precipitation results from the temperate maritime climate of Britain.
The breeding biology; clutch size and development of eggs and young, is similar throughout its Holarctic range, (8,9,15). However, there is a difference in the survival rate, it normally being lower amongst the Sand Martins breeding in the Western Palearctic.(8,15).
