248 THE BIRDS OF THE BRITISH ISLES. 



of the March Cuckoo. Yet many fail to realise that we have 

 three swallows and that this species is seldom the first to arrive. 

 The true Swallow can be identified by its continuous blue back, 

 chestnut and blue breast bands and long tail-streamers ; the 

 House-Martin has a white rump and under parts and shorter 

 tail ; the Sand-Martin, a smaller bird, is brown above and 

 white below, except for a band of brown across the breast. 

 About the middle of March the first Swallows arrive ; but it is 

 often well into April before they reach northern shires, and 

 May when they are seen in Scotland. Continuous waves of 

 Swallows come in until early June, but the later arrivals are 

 mostly passage birds. Normally the Swallow is a day migrant, 

 consequently its movements can be observed, but the passage 

 birds feed as they travel, and the ultimate direction of flight is 

 not always plain. Thus a steady stream of birds may be 

 travelling north, but individuals sweep back again and again to 

 work a good feeding ground ; yet the birds hawking to and fro 

 in one spot may be miles away in a few minutes and others 

 have taken their place. On southward migration — at its height 

 in late September— the flight is often steadier ; large parties of 

 mature and immature birds pass over, frequently at a height, 

 swerving but little though beating up into the wind and tacking, 

 yet always bearing south. Here again diurnal flight and the 

 need of rest leads to confusion, for flocks will gather from all 

 directions at a favourite roosting place. When this is reached 

 the flocks will pass and repass before settling down. The 

 height at which these autumnal migrants travel depends upon 

 wind and weather; at times it is beyond our vision. Some 

 interesting observations have been made from aeroplanes ; one 

 man, flying at 9500 feet, saw " Swallows " far above him, and 

 though distance may have prevented specific identification, 

 there is no doubt about the family. Against a strong wind the 

 birds travel low ; when crossing seas often merely skimming the 

 waves. 



