BRITAIN'S BIRDS AND THEIR NESTS. 271 



On autumn days, before they cross the sea, 



And to each bulrush-crest a Swallow hangs 



Quivering, and others skim the river stream, 



And their quick twittering fills the banks and shores. 



It was probably the habit of congregating in the 

 neighboui'hood of water in autumn and spring that gave 

 rise to the superstition that Swallows spend the winter 

 under water. 



Not so easily to be dismissed is the theory that 

 Swallows hibernate in holes. We cannot positively dis- 

 prove the existence in birds of a hibernating habit such 

 as exists both among mammals and reptiles, but in view 

 of its extreme improbability we need not seriously con- 

 sider the matter unless more substantial evidence is 

 produced. The evidence there is may easily be explained 

 away. 



Gilbert White was fully aware that Swallows migrated, 

 but he stoutly upheld his belief that a small number 

 hibernated. He could not believe that the young birds 

 of late broods were able to undertake the southward 

 journey when only a few weeks old. But we have no 

 reason to doubt that they at least attempt the journey. 

 Moreover, a young Swallow leaves the nest practically 

 full-grown and well able to fly, and a few weeks' prac- 

 tice must make it almost as strong on the wing as an 

 adult. 



There are numerous records of 'Swallows' being found 

 in holes in a torpid state, and reviving on being warmed. 

 A 'laggard' Swallow surprised by wintry weather might 

 conceivably — more especially if it were really a Sand- 

 Martin — have taken shelter in a hole and become 

 comatose from starvation ; but there is no reason to 

 suppose that it would have survived for any length of 

 time if it had not been rescued. 



