The Sand martin is a small migratory bird in the swallow family. It is brown above and white below with a narrow brown band on the breast. Its bill is black and the legs are brown. The brown back, white throat, small size, and quick jerky flight of the Sand martin separate it at once from similar swallows, such as the Common house martin, the American cliff swallow.
Sand martins have a wide range in summer, embracing practically the whole of Europe and the Mediterranean countries and across the Palearctic to the Pacific Ocean. They are also found in North America. Sand martins winter in eastern and southern Africa, South America, and the Indian Subcontinent. These birds are generally found near larger bodies of water, such as rivers, lakes, or even the ocean, throughout the year. They forage in open areas such as grassland and farmland and tend to avoid dense forests and mountainous areas.
Sand martins are very social birds that live and nest in colonies. They are active during the day and spend their time foraging, preening, and often sunbathe in groups. At night they gather in communal roosts. Sand martins are fast and agile fliers. They rarely land on the ground and are often seen perching or in flight. These birds usually forage in the morning singly or in groups; they catch insects on the wing and occasionally on the ground or over the water. Sand martins constantly communicate with each other; their twittering song is continuous when the birds are on the wing and becomes a conversational undertone after they have settled in the roost. The harsh alarm is usually heard when a passing falcon, crow, or other suspected predator requires combined action to drive it away.
Sand martins are carnivores (insectivores). Their diet consists of small insects, mostly gnats and other flies whose early stages are aquatic.
Sand martins are serially monogamous and pairs remain together for the nesting season. They appear on the breeding grounds starting towards the end of March and leave by the end of September. Sand martins are sociable in their nesting habits; from a dozen to many hundred pairs will nest close together, according to available space. The burrow is excavated by the male first and then he will perform territorial circle flights around the burrow entrance while singing, trying to attract females. When the pair is formed, both birds complete this work. The tunnel is dug in sand or gravel soils. The nests are placed at the end of tunnels which are 50 to 100 cm long and lined with straw and feathers. The female lays 4-5 white eggs and both parents incubate them for 14-15 days. Pairs usually produce two broods in one breeding season. The chicks are helpless (altricial) and cared for by both adults. They fledge and leave the nest around 18 to 22 days after hatching but remain dependant on their parents for up to a week more. The young will then reach reproductive maturity in their first year of age.
Sand martins are not considered globally threatened. However, certain populations have declined or face threats from habitat loss and fragmentation. They also suffer from the use of pesticides and droughts in their wintering grounds.
According to the IUCN Red List, the total Sand martin population size is 10,000,000-500,000,000 mature individuals. The European population consists of 3,640,000-8,000,000 pairs, which equates to 7,280,000-16,000,000 mature individuals. National population estimates include around 10,000-100,000 breeding pairs and around 1,000-10,000 individuals on migration in China; around 100-10,000 breeding pairs and less than 50 wintering individuals in Japan, and around 10,000-100,000 breeding pairs and around 1,000-10,000 individuals on migration in Russia. Overall, currently, this species is classified as Least Concern (LC) on the IUCN Red List but its numbers today are decreasing.
Sand martins control populations of a wide range of insects that they consume in their diet. Due to their habits to excavate burrows, these birds also provide shelter for other bank burrowing birds such as house sparrows, European starlings, kingfishers, barn owls, and swallows.