1902 Reptile Studies 21 



ingly. But a large number of mammals are nocturnal in 

 their active habits, sleeping during the hours of daylight ; 

 this habit of life being necessitated on account of the per- 

 secution they suffer in the daytime, or from the fact that 

 the food on which they depend for sustenance is only to 

 be obtained in the hours of darkness. Most of these noc- 

 turnal mammals, or at any rate many of them, undergo a 

 period of hibernation of shorter or longer extent, the length 

 of the hibernation often varying with the severity of the 

 winter, and being very different in some species from others. 

 As far as mammals are concerned, the bats exhibit by far 

 the deepest hibernation in this country : one of them, the 

 serotine bat, retires for six months of the year, being seen 

 but seldom before May, and disappearing again about the 

 end of September. The other bats are also torpid for 

 varying periods, being found hanging head downwards in 

 caves, holes in trees, barns, and church steeples, according 

 to the habitat of the individual species. It is said by some 

 that the winter sleep of the shrews — also nocturnal mam- 

 mals — is deeper than that of the bats, and certainly these 

 little animals are very seldom aroused by any unusual 

 warm weather which may come during the winter months. 

 Badgers do not really hibernate, their sleep in winter 

 being very broken, and never reaching true torpidity. 

 Squirrels are to be seen in full activity during the most 

 severe weather, though their appetite is not so voracious 

 as in the summer months, and is largely supplied by ac- 

 cumulated stores of nuts and acorns laid up in advance. 

 The dormouse, on the other hand, has a regular period of 

 hibernation, generally retiring from active life in October ; 

 but if roused this species does not suffer the same ill effects 

 as do the bats, interference with whose hibernation is often 

 fatal. Warm sunny days will bring out the field-vole, only 

 to sleep again when frost returns. But this torpidity of 

 many of our smaller mammals is very different in degree 

 and in character from that most remarkable physiological 

 condition of true hibernation to be seen in the reptiles (we 

 pass over the birds, as in them we have the phenomenon 

 of migration replacing hibernation in those species which 

 iind the winter too severe to remain where they breed). 



