Animal Behaviour 



by the ominous meaning of the splash of the first. The sudden 

 splash made by a frog leaping into water is associated with danger, 

 since a frog is not likely to leap into the water unless it is startled 

 — it walks or jumps short distances to the edge of the water, 

 slips lightly into it, and swims. This splash, then, puts a frog 

 into a waiting state of unusual keenness of sight and alertness 

 of muscle. The frog may lift the head or take on a more atten- 

 tive pose, but usually the only external evidence of this alert state 

 is a changed rate of breathing. The throat movements are more 

 rapid, except in cases where the attention demanded, or the fear 

 induced, is relatively intense; in such a case, the breathing move- 

 ments may cease altogether for several seconds at a time. 



It is not only the result of out-of-door observation, but it 

 has been proved by experiment that a frog does not give a mo- 

 tor response to sound alone (an illustration of a true inhibition 

 phenomenon), but that a sound stimulus intensifies the effect 

 of an accompanying visual or other stimulus. This explains not 

 only the instances given, but many others. It means, for instance, 

 that if the frog hears an insect before seeing it, he is put on the 

 alert, so that when he sees it his dash for it is more vigorous and 

 effective than it would have been with the visual stimulus alone. 

 The gopher frog of Florida, sitting at the mouth of its burrow, 

 hears a crunching on the sand or a crackling of twigs, and be- 

 cause of the warning of his ears is ready to beat a more vigorous 

 retreat when the enemy appears than he otherwise could. It 

 is unfortunate for the frog that the approach of the snake is so 

 soundless, and that the heron hunting at the pond is so often 

 statuesque and silent. 



Frogs can hear sounds made in air, whether the frog's ear 

 is in air or under water. It is thought that the hearing is keenest 

 when the ear-drum is half in air and half in water. Frogs can 

 hear sounds of both high and low pitch. The green frog is said 

 to hear sounds varying in pitch from 50 to 10,000 vibrations 

 per second. In captivity, frogs prove constantly that they hear 

 sounds of all sorts. They often respond with croaking when the 

 sound stimulus is non-startling in character, whether that stim- 

 ulus be the croaking of another frog, the sound of running wa- 

 ter, or of human voices. It is probable that one of the most 

 ominous sounds in the ears of a frog is the pain-scream of one 

 of its own species. This is a high-pitched sound produced with 



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