254 THE BIRDS OF THE BRITISH ISLES. 



in ever-increasing flocks, which, as the season advances, may 

 be seen gathering in trees or on house-tops and roping the 

 wires with Swallows. A few days before the exodus they will 

 wheel and dart in swarms round church towers or tall buildings ; 

 sometimes twittering hundreds collect in a tree, the centre of 

 their aerial exercise. Towards the end of October these 

 gatherings cease, though belated birds in November and 

 December are not uncommon. A friend of mine saw a solitary 

 bird hawking for flies in a gorge on the Cornish coast early in 

 February, but it is impossible to say if it had wintered or was 

 an abnormally early pioneer. 



The adult House-Martin is steel-blue above with a white 

 rump, and white under parts ; even its short legs and toes have 

 white downy feathering. Its bill is black, its irides brown. 

 The young bird is sooty black, and some of the coverts and 

 quills have white tips and edgings. Length, 5*3 ins. Wing, 

 425 ins. Tarsus, '45 in. 



Sand-Martin. Riparia riparia (Linn.). 



The Sand-Martin (Plate 102) has a wide range in summer, 

 embracing practically the whole of Europe and the Medi- 

 terranean countries, part of northern Asia and North America, 

 and eastern and southern Africa, southern Asia and South 

 America in winter. In the British Isles it is an abundant, 

 though rather local summer visitor and bird of passage. 



Towards the end of March, just in advance of the Swallow, 

 the Sand-Martin appears, first of its family, flitting over the 

 larger sheets of water in search of early flies. Its brown back 

 and small size and quicker, more jerky flight separate it at once 

 from the two blue-backed swallows. Later parties accompany 

 Swallows, but for a time, varying according to weather, the bird 

 remains at these large waters and does not visit its nesting 

 haunts. All day it flies from end to end of its selected pool, 



