272 MIGRATION OF ANIMALS. 



of climate, is a periodical MIGRATION. In this way they are 

 enabled to live throughout the year in a temperature conge- 

 nial to their constitution. 



* The extensive and numerous migrations of birds have 

 been noticed by mankind from time immemorial. They are 

 accompanied by many circumstances of a curious and inter- 

 esting nature, and have given rise to a good deal of speculation. 

 The different species of swallow, in particular, have excited a 

 large share of attention, and the place of their winter residence 

 has been the subject of much doubt.' With regard to these 

 birds, some naturalists are inclined to think that they do not 

 leave the place of their summer residence at the end of autumn, 

 but that they lie in a torpid state, till the beginning of summer, 

 in the banks of rivers, the hollows of decayed trees, the re- 

 cesses of old buildings, the holes of sand-banks, and in similar 

 situations. That swallows, in the winter months, have some- 

 times, though very rarely, been found in a torpid state, is un- 

 questionably true. Neither is the inference, that, if any of 

 them can survive the winter in that state, the whole of them 

 may subsist, during the cold season, in the same condition, in 

 the smallest degree unnatural. Still, however, the numbers of 

 swallows which appear in Great Britain, as well as in all parts 

 of Europe, during the summer months, are so very consid- 

 erable, that if the great body of them did not migrate to some 

 other climate, they would be much more frequently found in a 

 torpid state. On the contrary, when a few of them are dis- 

 covered in that state, it is regarded as a wonder even by the 

 country people, who have the greatest opportunity of stum- 

 bling upon facts of this kind. When, accordingly, a few 

 swallows or martins are found torpid in winter, and have been 

 revived by a gentle heat, the fact and few such facts there 

 are is carefully recorded as singular in all the periodical 

 publications of Europe. 



Instances of swallows and some other birds alighting on the 

 masts and cordage of vessels, at considerable distances from 

 any shore, are not so numerous as might be expected. Neither 

 have they been often observed flying over seas in great flocks. 

 Mr. Peter Collinson, in a letter printed in the Philosophical 

 Transactions, says, " that Sir Charles Wager had frequently 

 informed him, that in one of his voyages home in the spring, 

 as he came into soundings in our channel, a great flock of 

 swallows almost covered his rigging; that they were nearly 

 spent and famished, and were only feathers and bones ; but 

 being recruited by a night's rest, they took their flight in tha 

 morning." 



