AMERICAN BATS — ^HANDLEY 179 



p. 29) stated that semi-lethargic individuals were able to "hiss" when 

 disturbed. Mohr (1933, p. 50) reported that E. L. Poole made the 

 following observations on the call of an individual less than a week old: 

 "It has a ventriloquial hollow cuc-cuc-cuc, like a yeUow-billed cuckoo; 

 close at hand a high thin tse-tse-tse, like the song of a blackpoll warbler, 

 which could be heard synchronized with the other sound." 



Hibernation: Hibernation in an animal is a state of lethargy in 

 which body temperature is depressed in correspondence with a low 

 environmental temperature and in which physiological activity is 

 proportionally curtailed. Hibernation may be of long or short dura- 

 tion. Among bats there appears to be no clear distinction between 

 sleep and hibernation. When the bat rests its temperature approaches 

 that of its environment. Thus, without regard for season, if the air 

 temperature of its roosting place is low enough, the bat assumes a 

 lethargic condition. 



However, Twente (1955b, p. 713) found that the body temperature 

 of bats difl&cult to awaken and bats easy to awaken may be the same. 

 He postulated that the degree of lethargy is dependent upon how high 

 or how low the bat's body temperature has been during the period of 

 lethargy. This factor would determine the amount of stored food 

 that had been catabolized during the period of inactivity. The pri- 

 mary wastes of this process are carbon dioxide, nitrogenous byprod- 

 ucts, and water. The observation that Myotis nearly always urinates 

 when awakened suggested to Twente that a possible factor causing 

 awakening is the amount of urine in the bladder and the nervous con- 

 sequences of bladder distension. He proposed that it would be more 

 appropriate to refer to the bat's lethargic state in degrees of irritabil- 

 ity rather than in degrees of lethargy. Thus, bats hibernating in 

 places that are warm or have fluctuating low temperatures are usually 

 more irritable than those that have been hibernating in places that 

 have relatively constant low temperatm^es. Similarly, bats at the 

 edges of clusters tend to be more irritable than those in the center, 

 for they have been members of the cluster the shortest time and have 

 higher temperatures and a higher rate of metabolism. If the place 

 that the bat has selected for hibernation is unsuitable, the animal 

 awakens, probably because a high metabolic rate has made it irritable, 

 and moves to another place. The bat always awakens and moves 

 when the temperature of its environment approaches 32° F. 



Twente (loc. cit.) found that once the awakening process is initiated, 

 the bat's body temperature rises at a constant and rapid rate (about 

 1.8° F, per minute for P. townsendii) until flight becomes possible for 

 the animal. Keeder and Cowles (1951, p. 395) determined the thresh- 

 old of flight to be at a rectal temperature of 73.9° F. in P. tovmsendii. 

 Twente's specimens of this species flew at a rectal temperature of 



