VII LANGUAGE OF BIRDS 367 



completely are tliey inherited — so much the less variable is 

 the mechanism of the vocal organs which is developed. 



Nevertheless, the languages of animals have their dialects, 

 possibly even that of the same species differs in different 

 regions. Any one who has passed sleepless nights in Naples 

 in the oppressive heat of August, will have discovered that 

 the crowinsj of the cocks there is different from that of ours 

 at home : they shriek in the most unmelodious fashion with 

 a force which goes to one's marrow. Possibly the creatures 

 have developed their great power of voice in order to make 

 themselves heard above the noise of the streets, and the 

 peculiarity has been gradually confirmed by heredity in 

 course of time. 



In our gardens the blackbirds give warning to all other 

 birds when a cat makes its appearance. As soon as one of 

 these beasts of prey shows itself they follow it from branch 

 to branch, uttering the cry "dag, dag, dag," in rapid suc- 

 cession, the greater their alarm the quicker the tempo. Then 

 the smaller birds come and join them with a confusion of 

 anxious cries. At evening, when twilight comes on, the 

 blackbirds utter the same cry for a time, but then it is not a 

 warning cry, and the other birds do not so interpret it. At 

 this time the blackbirds fly about as though quarrelling, 

 scolding, and pursuing one another before they go to sleep. 

 The meaning of this behaviour I have not been able to dis- 

 cover. When the blackbirds first see anything which makes 

 them anxious — as when they first catch sight of a cat — they 

 utter once only, flying from one place to another, a short 

 succession of sounds which, as far as I remember, is something 

 like " diridiridiridirollo." Now, I have noticed that the black- 

 birds of different districts, for instance those of the mountains 

 at certain places where I listened to them, in comparison 

 with those of Tubingen, present in these cries very con- 

 siderable, even surprising differences. Local variation of the 



