112 ANIMAL LIFE OF CARLSBAD CAVERN 



Their numbers must thus run into the hundreds of 

 thousands or into millions, and such numbers would be 

 necessary to account for the great deposits of guano 

 once found in the cave. It is well known that in the 

 fall these bats leave buildings and any quarters exposed 

 to low temperatures and return again in spring. 



Hibernation, or the complete torpor in which the 

 temperature of the animals' bodies becomes approxi- 

 mately that of the air, and all the life processes are 

 reduced to the lowest stage that will maintain life, is 

 probably continuous with the bats for about five 

 months, from October to March, but more or less 

 intermittent in fall and spring. On my arrival at the 

 cave, March 11, some of the bats came out on warm 

 evenings, and at least a part of them returned in the 

 morning, but a series of cold nights kept them in for 

 a week or more at a time. A few would be found flying 

 about in the cave during the evening, but only a com- 

 paratively small number, and these would not go out 

 into the cold outer air. The air at the bottom of the 

 room under the bats was usually 55 degrees Fahrenheit 

 during March and April, and is said to vary but little 

 throughout the year. Unfortunately, the hibernating 

 colonies of bats in the cave were so far out of reach 

 that a satisfactory study of temperatures and conditions 

 could not be made. 



The bats captured and kept in captivity became 

 torpid at night when the temperature fell to 50 degrees 

 Fahrenheit, and showed about the same body tempera- 

 ture as the air. They were stiff and unconscious, able 

 only slowly to move a foot or wing when disturbed, or 



