BIRDS — 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. Resting 
1 For full information, see Buckland, Curiosities of Natural History , 
p. 183. 
2 Of the crow (carrion and hooded), Edward says : 4 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.’ 
