SNAKES AND FIELD MICE. 53 



very numerous. He says : " In the autumn of the year [May, 1873] 

 countless number of storks (Ciconia maguira \Euxenura maguira]) 

 and short-eared owls (Asio accipitrinus) made their appearance. 

 They had also come to assist in the general feast. * * * Years 

 have perhaps passed during which scarcely an individual of these 

 kinds has been seen; all at once armies of majestic white storks are 

 seen conspicuously marching about the plain in all directions, while 

 the night air resounds with the solemn hootings of innumerable 

 owls." a European writers bear testimony to the usefulness of the 

 common stork (Ciconia ciconia) in destroying voles and other kinds 

 of mice. 



The family of cranes (Gruidce) range farther north than the 

 herons, and the three North American species are known to feed to 

 some extent upon voles, capturing both young in the nests and adults. 

 The habitat of cranes includes upland prairies as well as moist 

 meadows, and thus probably they prey upon more species of voles 

 than herons do. 



Although the usual food of gulls (Laridce) consists of fishes and 

 insects, they feed also upon rodents. During the vole outbreak in 

 Scotland in 1892 several species of gulls, notably the great black- 

 backed gull (Larus marinas), fed upon the field mice; and gulls are 

 usually named among the species that feed upon lemmings during 

 their migrations. It is highly probable that the larger American 

 gulls feed upon field mice whenever they find them. 



Snakes. 



Snakes must be included among the natural enemies of field mice. 

 While nearly all snakes feed extensively upon, insects, many of them 

 eat vertebrates, including fishes, reptiles, batrachians, birds, and 

 mammals. The larger bull snakes (Pita op his) , black snakes (Cal- 

 lopeltis), and rattlesnakes (Crotalus) of the United States feed 

 largety upon mammals, including rabbits, prairie dogs, pocket go- 

 phers, and ground squirrels, as well as different species of rats and 

 mice. Black snakes and bull snakes probably kill more field mice 

 than the others ; but black snakes destroy also a considerable number 

 of nestling birds and birds' eggs, so that part of their beneficial 

 work is offset by this injurious habit. A nurseryman in Pennsyl- 

 vania reports that he secured immunity from mice in his nursery by 

 turning loose in it 50 black snakes. On the whole, snakes, except 

 the venomous species, are deserving of the farmers' protection. Like 

 the toad, the smaller kinds feed almost wholly upon insects; but an 

 inherent prejudice induces thoughtless people at every opportunity 

 to destroy these friends of agriculture. 



o Naturalist in La Plata, pp. (J4-G5, 1892, 



