144 MY NATURE NOTEBOOK. 



reappear in early autumn at intervals in districts 

 which he seemed to have already forsaken. These 

 seeming reappearances are, no doubt, the arrivals of 

 fresh contingents from further north, travelling south- 

 wards while a cold wind drives the flies to shelter, 

 and halting to feed and enjoy life when the genial 

 south wind tempts insect life abroad again. 



THE SWALLOW'S ADVANTAGE. 



The swallows and martins are less ready to take 

 a hint from the north wind. In tireless flight they 

 winnow daily such large spaces of the air that even 

 when the wind is chill in early September it blows 

 enough small insect life to leeward of tree and 

 hedgerow to support them. Besides, many of them, 

 especially the house-martins, who arrived late, have 

 young still in the nests ; and because these are 

 obliged to stay the others halt with them as long as 

 possible. Presently there will come an unmistakable 

 cold nip into the air, which even the martins and 

 swallows must obey ; but, since they can always 

 outdistance the wind in a few hours' flight, they gain 

 rather than lose by staying till the last moment. 

 The youngest of them grow strong on the wing by 

 daily practice ; and if they departed with the cuckoos 

 and butcher-birds, or even with the earliest warblers 

 and fly-catchers, they would have to abandon their 

 habit of rearing late broods, and thus diminish their 

 rate of multiplication. 



