BIKDS SPECIAL HABITS OF FEEDING. 283 



Taking first those special habits connected with the 

 procuring of food, we may notice the instinct manifested 

 by blackbirds and thrushes of conveying snails to con- 

 siderable distances in order to hammer and break 

 their shells against what may happen to be the nearest 

 stone, 1 and the still more clever though somewhat analo- 

 gous instinct exhibited by certain gulls and crows of flying 

 with shell-fish to a considerable height and letting them 

 fall upon stones for the purpose of smashing their shells. 2 

 Both these instincts manifest a high degree of intelligence, 

 either on the part of the birds themselves, or on that of 

 their ancestors ; for neither of these instincts can be re- 

 garded as due to originally accidental adjustments favoured 

 and improved by natural selection ; they must at least 

 originally have been intelligent actions purposely designed 

 to secure the ends attained. 



An interesting instinct is that of piracy, which in the 

 animal kingdom reaches its highest or most systematic 

 development among the birds. It is easy to see how it 

 may be of more advantage to a species of strong bird that 

 its members should become parasitic on the labours of 

 other species than that they should forage for themselves, 

 and so there is no difficulty in understanding the develop- 

 ment of the plundering instinct by natural selection. We 

 find all stages of this development among the sea-birds. 

 Thus the gulls, although usually self-foragers, will, as I 

 have often observed, congregate in enormous numbers 

 where the guillemots have found a shoal of fish. Eesting 



1 For full information, see Buckland, Curiosities of Natural History, 

 p. 183. 



* Of the crow (carrion and hooded), Edward says : ' He goes aloft 

 with a crab, and lets it fall upon a stone or a rock chosen for the 

 purpose. If it does not break, he seizes it again, goes up higher, lets it 

 fall, and repeats his operation again and again until his object is 

 accomplished. When a convenient stone is once met with, the birds 

 resort to it for a long time. I myself know a pretty high rock, that has 

 been used by successive generations of crows for about twenty years !' 

 Also, as Handcock says, ' a friend of Dr. Darwin saw on the north coast 

 of Ireland above a hundred crows preying upon mussels, which is not 

 their natural food ; each crow took a mussel up into the air, twenty 

 or forty yards high, and let it fall on the stones, and thus breaking the 

 shell, got possession of the animal. Ravens, we are told, often resort 

 to the same contrivance.' 



