SWALLOWS AND SWIFTS 151 



place her egg in a sand-martin's nest, and very difficult for 

 her to get it unbroken into a house-martin's ; but it is not 

 very rare for a swallow's nest to harbour a cuckoo, though 

 the swallow is not one of the cuckoo's usual victims. 



Our British swallows and swifts spend the winter in various 

 parts of tropical and southern Africa ; some of them also 

 occur in winter in India, but these are probably birds from 

 northern Asia. Very early in the spring the three species of 

 swallow and martin begin to work their way north. They 

 follow the wave of spring warmth which brings out the 

 insects on which they feed. There is thus a considerable 

 difference in the date of their reappearance in south-west 

 France and southern England, or even in the south of 

 England and Scotland. By early April, when the single 

 pioneers that proverbially do not make summer are seen in a 

 few scattered districts, swallows are already abundant among 

 the meadows and vineyards of the Loire ; and they settle 

 about the farms of the Thames and Severn valleys at least a 

 month before they reach their furthest haunts in the north of 

 Scotland. The house-martin and sand-martin usually arrive 

 a little earlier than the swallow. Since they depend entirely 

 for food on flying insects, and cannot pick among the boughs 

 for larvae or pupae like most of the summer warblers which 

 arrive about the same time, the swallows have a peculiarly 

 pitiful appearance when, as happens every few years, a bitter 

 spell of April frost and east wind greets them as soon as they 

 arrive. They are seen flying feebly and dispiritedly above 

 sheltered waters, and are often found dead in or beneath 

 their old nests. The impulse which urges them to return to 

 the summer home has no power of warning them of unsuit- 

 able weather there ; they migrate because it feels like spring 

 where they are, and they are always liable to be trapped by 

 the treacherous spring changes of the English climate. If 



