HEARING — FIELDWORK AND EXPERIMENTS 77 



that they have received the sounds given out by the male, 

 but also that his courtship "song" has a particular signifi- 

 cance for them. 



Amphibia 



The use of vocal sounds among frogs and toads can be 

 observed any spring by first locating a pond used by one or 

 other amphibian. It is best to do this well before the normal 

 time when these creatures migrate to their ultimate spawning 

 places. The males do all the real croaking (though females 

 can utter sounds as well) and they are usually the first to 

 come out of hibernation and make their way to the ponds. 

 Incidentally, it has not yet been definitely established exactly 

 how toads, at least, locate their ponds with such precision 

 year after year ; but when this problem has been fully solved, 

 it is likely that it will be discovered that one of the normal 

 senses — possibly smell — is used and not any mysterious extra 

 sense. 



Once at the ponds, the males start croaking and are soon 

 followed by the females, though it is most improbable that 

 croaking serves as any guide towards the water ; for if this 

 were so what would guide the first of the males? The frogs 

 or toads, having congregated in the pond, croaking is thought 

 by most of us who have studied these animals to be used for 

 keeping the colony together. 



There seems to be little real rivalry among Common Frogs 

 or Toads ; but in the case of the Marsh Frog and the Edible 

 Frog there is evidence that the males take up special croak- 

 ing points or situations which they will defend against other 

 males. 



I have spent a great deal of time observing these species — 

 especially the Marsh Frog in the Romney Marsh area in 

 Kent; and not only I, myself, but other naturalists and 

 zoologists with whom I have had the pleasure of working, 

 have seen this territorial defence behaviour going on. (See 

 Plate 4.) 



One male will take up his chosen position and will com- 

 mence to utter his loud and very distinctive call. Often 

 another male, which has not yet secured a favoured site, will 



