Sand martin life cycle
Sand martins are summer visitors to the UK. they are one of the first spring migrants to appear, arriving mid-March to mid-April, with late arrivals up until June.
Sand martins are very gregarious and nest in colonies, which may contain more than 100 pairs. They excavate tunnels in sandy, dry vertical banks in sand pits and gravel pits, railway cuttings, riverbanks and sea-cliffs, and exceptionally in drainpipes in walls, and holes in brickwork.
Both males and females make a horizontal tunnel 45-90 cm long with a chamber at the end. Suitable sites may be used for years. New tunnels will be dug as the cliff collapses, or as old holes become too big (when they may be taken over by sparrows or starlings).
The white eggs, usually four or five, sometimes three to seven, are generally laid in late May or early June in a nest of feathers, grass and leaves. Incubation is by both parents once the last egg is laid, and lasts for about 14 days. All eggs hatch at the same time.
The young are helpless and remain in the nest. They are bed by both parents and fledge when 19-24 days old. After fledging, they are dependent on the parents for about one week. Usually two broods are raised each summer.
The birds depart British Isles 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.