CHIROPTERA 29 



All British species are liable to enter the lethargic condition 

 should the temperature fall low enough, but they may rapidly 

 awake in response to heat, as when warmed in the hand, so that 

 their lethargy is never very profound. At such times the body- 

 temperature rises rapidly, sometimes as much as 31° Fahren- 

 heit in fifteen minutes, the muscles shudder, the animal pants 

 and throbs, becomes lively, squeaks, and is fully awake. Before 

 commencing hibernation, bats are, as a rule, very fat, their 

 weight being appreciably greater than in early summer, at 

 which time some species are thin. Mr Hahn believes that the 

 degree of lethargy bears a close relation to the supply of super- 

 ficial fat, and is not connected with temperature or season. The 

 American bats examined by him became more active as the 

 winter advanced, but this is contrary to British observations. 

 At all times, as in Britain, there was much irregularity of 

 movement amongst individual bats. 



The more general belief is, however, that the duration and 

 depth of the hibernatory sleep depend largely, although not 

 entirely, on temperature, and consequently on locality and 

 season. In warm climates bats, like hedgehogs, probably do 

 not hibernate at all, while in the temperate regions, such as 

 Britain, the process is by no means constant, but varies with 

 the species, for each of which there is no doubt a definite 

 temperature inducing torpidity. Individuals, however, may 

 constantly be found abroad at exceptional temperatures, but 

 the body never becomes so physiologically awake as to ovulate. 



Leisler's Bat is probably one of the earliest to discontinue 

 flying, and in Ireland, although it has been observed so late as 

 the 1 6th November, the majority as a rule disappear about the 

 end of September. Its congener, the Noctule, has been 

 observed abroad in every month except January, but its winter 

 appearances are the exceptions that prove the rule. The Long- 

 eared is more hardy and is frequently caught in winter : it 

 probably shifts its quarters at intervals throughout the winter. 

 The Barbastelle has been taken on New Year's Day. A 

 Daubenton's Bat has been found on the wing at a temperature 

 of 42° Fahrenheit, and another contained recently digested 

 food in December. Natterer's leaves its winter quarters in 

 February, while the Horseshoes, the Whiskered, and the 



