8 THE MIGRATION OF BIRDS, 



Before proceeding further with this interesting 

 subject, it will now be necessary to say a few words 

 on what avian hibernation really consists of. Hiber- 

 nation, according to the testimony of observers, 

 may aptly be divided into two kinds. The first 

 division we may designate as subaqueous hiberna- 

 tion, in which birds were said to plunge under the 

 surface of water, and to bury themselves in the 

 mud at the bottom. The second division we will 

 call terrestrial hibernation, and is similar to that 

 prevailing amongst bats and various other mammals, 

 in which birds were said to hide themselves away 

 in crevices of rocks, in hollow trees, and such-like 

 warm and sheltered nooks, there to sink into lethargic 

 slumber until the return of a warmer temperature. 

 So far as the actual process of hibernation is con- 

 cerned, it does not appear to differ in any way from 

 that undergone by bats or other mammals ; the 

 vital functions are partially arrested, animation is 

 suspended, and a death-like trance or stupor, a 

 lethargic sleep, eventually supervenes. Birds that 

 are said by observers to have been discovered in 

 this state, have slowly regained animation upon 

 being subjected to a warmer atmosphere or to any 

 external heat. 



It would be a very easy matter to fill scores of 

 pages with what appear to be well-authenticated 

 instances of the hibernation of birds ; but it will 

 be sufficient for our purpose to allude to a few of 

 the most striking and authoritative ones. In 1666, 

 Schefi^erus records in the Philosophical TransactionSy 



