SENSORY ADAPTATIONS OF BATS. I 55 



After extended observations on the subject, I am still unable 

 to form any definite conclusions with regard to the importance 

 of sight to these animals. That they can see light and darkness 

 and moving objects is unquestionable. That the sense of sight 

 is not highly developed is equally certain. The behavior of some 

 of the animals appears to indicate that at times they depend on 

 this sense to a considerable degree, both in securing food and in 

 avoiding objects. 



On bright nights, and in twilight, a dark, moving object can be 

 readily seen against the skyline. Under such circumstances 

 sight would be of use to bats in helping them to find the general 

 location of food. Whether it really guides them at such times 

 is a point not yet determined. 



Bats are extremely sensitive to vibrations of high frequency, 

 A sharp whistle, sucking noises with the lips, tearing a sheet of 

 paper and drawing the finger nail across a piece of thin board or 

 rough cardboard cause them to start violently, but low pitched, 

 rumbling noises have no apparent effect. 



Flying insects usually produce a high-pitched hum. While 

 it would be of advantage to a bat to perceive these sounds, the 

 evidence that they are actually guided to their prey by hearing 

 them is inconclusive. It is not possible in observations on feed- 

 ing to distinguish between response to hearing and to tactile 

 stimulation, by the vibrations. The voice of different species of 

 bats varies but it is always high pitched. Alcock ('99) states 

 that the voice of the hairy-armed bat has about 17,000 vibrations 

 per second. The pitch has not been determined for the voice of 

 the American species. 



It is evident, however, that it is the motion of the insects that 

 lead to their perception by bats. Whitaker ('06) states that a 

 noctule which he observed caught a pebble tossed into the air. In 

 this country boys often gather under the electric lights or at the 

 edge of a wood where bats are abundant in the evening, and 

 knock them down with a fishing pole waved rapidly in the air. 

 In both cases the bats are attracted by the moving object and 

 probably by hearing. The tactile sense, located in the vibrissas 

 and lips, is certainly very delicate and doubtless aids the animal 

 to definitely locate its food. In feeding meal worms to bats I 



