SENSORY ADAPTATIONS OF BATS, 14/ 



Since they live a part of the time in the caves where there is a 

 total absence of light and where the temperature varies only a few 

 degrees throughout the year, the question has been asked, how 

 do they know when to come out (Blatchley, '96)? The answer 

 is, they try conditions and only come out under favorable circum- 

 stances. So far as I know, careful observations bearing on this 

 point have not hitherto been made and it seems worth while to 

 record my own in some detail. 



In the first place, hibernation among bats is not strictly com- 

 parable to the same process among the lower vertebrates, since 

 it is not one unbroken period of torpor more or less dependent 

 on temperature (Oldham, '05 ; Rollinat and Trouessart, '96). 

 The vital functions of a frog may be practically suspended during 

 a long period, the lungs and digestive organs almost ceasing to 

 function for the entire winter. In bats the activity of the vital 

 organs decreases, though only to a limited degree. The rate of 

 respiration is difficult to count accurately because the body 

 movement is slight. I have counted the respiration of a dor- 

 mant bat in the cave at several times during the winter and found 

 the rate to be about 60. At other times I have seen the animals 

 apparently cease to breathe for periods as long as four and a 

 half minutes, and then after one or two convulsive respirations, 

 the frequency would suddenly go up to as high as 82 per min- 

 ute. I am not certain that breathing actually ceased during the 

 quiescent period but there was no visible body movement. In 

 any case, the same conditions are found during profound diurnal 

 sleep at all seasons of the year. 



The animals do not obtain food during the winter but the 

 stored fat is used up and wastes are excreted from the body. 

 Oldham ('05) found fecal matter in the intestine of the lesser 

 horseshoe bat {RJiinolopJuis liipposideros) during the winter and 

 regarded it as proof that the animals had been eating recently. 

 However, fecal matter is, in part, derived from wastes excreted 

 through the wall of the lower part of intestine and is not depen- 

 dent upon food. The presence of feces is, therefore, no indica- 

 tion that an animal has recently eaten. Lusk' states that a fast- 



' "Science of Nutrition," Graham Lusk, p. 46. 



