11 



Vegetable feeders may prey on other animals. No mammal is 

 considered more carnivorous than the wolf, yet at times it 

 feeds voraciously on berries. My son saw a mink eating the 

 bark and foliage of fruit trees. Wallace says that the carnivo- 

 rous sable feeds partially on fruits or seeds in winter. 1 



It is a well-known fact that grain-eating birds have strong, 

 muscular stomachs or gizzards lined with a hard, corrugated 

 membrane which, with the assistance of pebbles, swallowed for 

 the purpose, triturates or grinds up the grain or other seeds 

 eaten, thus practically masticating them in the stomach. 

 Nevertheless, most birds provided with such a stomach readily 

 turn to animal food. It is well known, also, that flesh-eating 

 birds have soft stomachs not fitted for grinding grain, but 

 many of them will eat grain at need. Hon. John E. Thayer 

 informs me that, the hooded merganser (Lophodytes cuculatus), 

 a fish-eating duck, readily learns to eat corn. In the Shetland 

 Islands the herring gull (Larus argentatus) is said by Dr. Ed- 

 nionstone to live on grain in summer and fish in winter. 2 

 In America our closely allied species has not been recorded as 

 a grain eater. 



A bird may vary its food habits by necessity, and such a 

 change may even transform the lining of the stomach. Dr. 

 Hunter fed a seagull for a year on grain and at the end of that 

 time the appearance and structure of the stomach had so 

 changed that it resembled the gizzard of a pigeon, and Dr. Ed- 

 monstone asserts that the herring gulls of the Shetland Islands 

 thus produce a change in the structure of the stomach twice a 

 year as they shift from grain to fish. 



Similar transformations have been observed in the stomach 

 of a raven and that of an owl, and Dr. Holmgren has proved 

 by experiment that the stomachs of pigeons, fed for a long 

 time on meat, gradually come to resemble those of rapacious 

 birds. 3 



When it is shown how all animals tend to increase in num- 

 bers, and how readily some of the most useful may change 

 their feeding habits and become injurious under the spur of 



1 Wallace, Alfred Russell: Darwinism, 1890, p. 191. 



2 Semper, Karl: Animal Life as affected by the Natural Conditions of Existence, 1881, p. 61. 

 8 Ibid., pp. 67, 68. 



