the sand martin (riparia riparia) or european sand martin , bank swallow in the americas , and collared sand martin in south asia , is a migratory passerine bird in the swallow family .
it has a wide range in summer , embracing practically the whole of europe and the mediterranean countries , part of northern asia and also north america .
it winters in eastern and southern africa , south america and south asia .
this species was first described by linnaeus in his systema naturae in 1758, and originally named hirundo riparia; the description consisted of the simple cinerea , gula abdomineque albis"an ash-grey swallow , with white throat and belly"and the type locality was simply given as "europa" .
the specific name means "of the riverbank"; it is derived from the latin ripa "riverbank" .
the pale martin of northern india and southeastern china is now usually split as a separate species riparia diluta .
it has paler grey-brown upperparts and a less distinct breast band .
it winters in pakistan and southern india .
the 12 cm (4.7 in) long sand martin is brown above , white below with a narrow brown band on the breast; the bill is black , the legs brown .
the young have rufous tips to the coverts and margins to the secondaries .
its brown back , white throat , small size and quick jerky flight separate it at once from similar swallows , such as the common house martin (delichon urbicum), the american cliff swallow (petrochelidon pyrrhonota) or other species of riparia .
only the banded martin (r .
cincta) of sub-saharan africa is similar , but the sand martin only occurs there in (the northern) winter .
the sand martin's 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 heard when a passing falcon , crow or other suspected predator requires combined action to drive it away .
linnaeus already remarked on this species' breeding habits: habitat in europae collibus arenosis abruptis , foramine serpentino  "it lives in europe , in winding holes in sheer sandy hills" .
it is generally found near larger bodies of water , such as rivers , lakes or even the ocean , throughout the year .
the sand martin appears on its breeding grounds as the first of its family , starting towards the end of march , just in advance of the barn swallow .
in northern ohio , they arrive in numbers by mid-april in our time , about 10 days earlier than they did 100 years ago .
at first , they flit over the larger bodies of water alone , in search of early flies .
later parties accompany other swallow species , but for a time , varying according to weather , the birds remain at these large waters and do not visit their nesting haunts .
the sand martin departs early , at any rate from its more northerly haunts .
in august , the gatherings at the nightly roost increase enormously , though the advent and departure of passage birds causes great irregularity in numbers .
they are essentially gone from their breeding range by the end of september .
the food consists of small insects , mostly gnats and other flies whose early stages are aquatic .
the sand martin is sociable in its nesting habits; from a dozen to many hundred pairs will nest close together , according to available space .
the nests are at the end of tunnels of from a few inches to three or four feet in length , bored in sand or gravel .
the actual nest is a litter of straw and feathers in a chamber at the end of the burrow; it soon becomes a hotbed of parasites .
four or five white eggs are laid about mid-late may , and a second brood is usual in all but the most northernly breeding sites .
this is not a rare bird , and it is classified as a species of least concern by the iucn .
it does have some local protections , as certain populations have declined or face threats from habitat loss and fragmentation .
they are considered threatened in california , where populations exist in the sacramento valley and at two coastal sites , ano nuevo and fort funston .
