HEARING — FIELDWORK AND EXPERIMENTS 83 



between the tongues of parrots, starlings, and crows, yet all 

 can hear and store up and repeat very diverse sounds. The 

 syrinxes (voice-boxes) are the organs by means of which 

 birds utter their songs and cries; and these, too, differ in 

 their construction between group and group. It would be 

 interesting to know if the ears of the various mimicking birds 

 vary a great deal; for clearly the ability to mimic depends 

 on acute and selective hearing, because without such the 

 birds would not be able to hear and distinguish the sounds 

 they learn. 



All owners of talking birds are unconsciously experiment- 

 ing with the hearing of their pets, and though many probably 

 do not realize this, and consider that they are only concerned 

 with words and whistling, it is a pity that more of them do 

 not study the whole of this matter more thoroughly. Dr. 

 W. H. Thorpe of Cambridge University is at present devot- 

 ing much of his time to investigating this side of bird be- 

 haviour and, in due course, when his work is complete, we 

 shall probably learn a great deal more about both the vocal 

 and auditory apparatus of birds and the interpreting of their 

 sounds. 



Mammals 



In considering the hearing of mammals, we are dealing with 

 a sense which is probably as highly developed as the sense 

 of smell, though the mysteries of scent present features that 

 are by no means fully understood. In addition, those demon- 

 strations of scenting powers which we can observe may seem 

 to be more wonderful than those of hearing. Nevertheless, 

 the sensitiveness of hearing manifested in mammals can 

 hardly fail to impress the student. 



Mammals are the only creatures that have external ears, 

 or "ear-flaps" as they are sometimes crudely called. These 

 external ears are seen in great variety in different groups, 

 but all have the same basic function, which is that of con- 

 ducting sound to the inner ear and thence to the brain. The 

 external ears of some mammals are very mobile and are 

 capable of being turned this way and that so as to be able 

 to detect far-off sounds and to locate the origin of the sound 



