8o THE SENSES OF ANIMALS 



will have different roles : one must be the observer and the 

 other the person who, at the right time, makes a noise by 

 clicking fingers or crumpling dry leaves or bracken. 



The observer must walk slowly and silently towards some 

 known place; as soon as a lizard is seen basking he must 

 stop and remain quite still, keeping his eyes on the lizard — 

 a pair of binoculars can be most helpfiil in getting an early 

 sight of the quarry without disturbing it. As soon as the 

 observer stops moving, the assistant, who should try to be 

 in a position nearby, but so placed as to ensure that no 

 shadow falls across the lizard, must make the agreed noise. 

 If both persons have acted with caution and luck is good, 

 the observer should be able to see how the lizard either takes 

 up an alert posture or, if the noise be loud enough, will 

 scuttle to cover. A series of experiments of this kind, with 

 the noise being decreased each time, will again show the 

 high degree of hearing ability possessed by lizards. 



My own most impressive test was to obtain a reaction 

 from a sand lizard when my colleague had merely "clicked" 

 his finger and thumb-nails together a good eight paces from 

 the lizard. 



Birds 



In considering ways and means of observing and testing the 

 hearing powers of birds, we come to a group of animals 

 where sounds play an important part in their lives. Defend- 

 ing territory, courtship, alarm, and food finding, all have 

 some connection with a bird's ability to hear and utter 

 sounds; but this aspect of our subject is complex, because 

 the sounds vary much as between species and species, and 

 also according to the purpose for which the sound is made. 

 Once again, it must be remembered that no animal has a 

 sense well developed unless there is some use for it; and in 

 relation to hearing, it follows that birds utter different notes 

 to suit certain conditions. They hear and respond to the songs 

 and calls of their own particular species, and they also can 

 hear sounds made by other animals or by mechanical means. 

 They, therefore, have the ability to take in vibrations of 

 greatly differing wave-lengths, e.g. the high twittering of the 



