Sand Martin

Sand Martins are strongly migratory, with many making journeys of several thousand kilometres each year. Unlike other passerines, they migrate mostly by day stopping frequently en route to refuel. Before crossing barriers, such as the Sahara Desert or the Mediterranean Sea they will fuel for several days to ensure they have enough fat for the crossing. The amount of fat they lay down is closely correlated with the size of the barrier, carrying excess fat is extremely costly in terms of impaired flight performance. During migration, and in their winter quarters, birds will gather in large roosts, particularly in reedbeds and some types of crop for the night. This gregariousness is carried over into the breeding season, with most species nesting colonially to some extent.
Sand martins are summer visitors to Europe. they are one of the first spring migrants to appear in Europe, arriving mid-March to mid-April, with late arrivals up until June.
The birds depart their breeding grounds from late July to September. Most are thought to winter in the Sahel, the zone south of Sahara, where they feed in damp places that offer plentiful supplies of flying insects.