The sand martin feeds almost exclusively on insects caught in flight, although it also occasionally takes insects and spiders from the ground or from the surface of water. Sand martins may feed alone or in large flocks, usually over water or open ground, and often associate with other swallow species. This species has a fast flight, with distinctive shallow, fluttery wing beats (2) (3) (4) (6) (8).
The breeding season of the sand martin runs between April and August (3) (4). It is a highly social species, nesting in colonies that may number from 10 to nearly 2,000 pairs. The sand martin nests in burrows, which are typically crowded together in a natural or artificial bank, usually in fairly loose soils that are easy to burrow into, and near large bodies of water that give plenty of flying space (2) (3) (4) (8). The burrows are mostly built in the upper part of the bank, to avoid ground predators (2) (4).
The male sand martins arrive on the breeding grounds before the females (3) and begin to excavate a burrow, using the beak, feet and wings to dig. When the burrow reaches about 30 centimetres in length, the male attempts to attract a female by singing and flying around the burrow entrance (2) (3) (4). Once the female has chosen a mate and nest site, both adults complete the burrow, which can reach up to a metre or more in length (3) (4) (8). Generally, a new burrow is dug each year, but old burrows may sometimes be enlarged and reused if they have not been lost through the erosion of the bank or cliff face (3) (4).
An enlarged nesting chamber is built at the end of the burrow, inside which the nest itself is placed. Both the male and female sand martin help construct the nest, which consists of a mat of grass, rootlets, leaves, twigs, straw and feathers. Around 2 to 7 white eggs are laid, and are incubated, mainly by the female, for 12 to 16 days (2) (3) (4) (8). The young sand martins are cared for by both adults and leave the nest at around 18 to 22 days old, after which the adults continue to feed them for up to a week (2) (3) (4). For the first four or five days, the young may return to the burrow at night, often to one that is not their own (3) (4). The adult sand martins are able to recognise their own chicks by their individual calls (4). As the breeding season comes to an end, the adults and young gather in large flocks, often with other swallow species, before departing on the southward migration (3) (4) (8).
In North America, the sand martin usually only raises one brood each season, but in other parts of its range it commonly raises two. Young sand martins may breed from their first year, and this species has been recorded living to at least nine years old (3) (4).