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NORTH AMEKICAN FAUNA. 



[Xo. 12. 



meiit iu temperate Europe, Asia, and North America. Althoiigii it is 

 IDrobable tliat no species are common to both continents, five genera 

 and four subgenera of the genus Microtns have a circumpolar distribu- 

 tion. On the other hand, no genera are peculiar to the Old World, and 

 only two are confined to America. Asia has five subgenera of Microtus 

 not found in America, and America has three not known to occur in the 

 Old World. 



HABITS. 



The voles and lemmings occur in great abundance throughout the 

 region which they occupy. They live in an endless variety of situa- 

 tions, from sea beaches to marshes and Alpine mountain tops, and from 

 open plains to the densest forests. They are, perhaps, most numerous 

 in well-watered grass lands. In localities where they are abundant 

 most of the species make their presence known by trails or runways 

 traced through the vegetation near their burrows. Occasionally, how- 

 ever, they occupy hollows in decaying logs or among loose rocks, and 

 use natnral crevices instead of beaten j)aths. While the great majority 

 of species spend much of their time on the surface, protected hj the 

 overhanging vegetation, a few live almost exclusively -underground, 

 and in consequence of this habit have acquired numerous modifications 

 which fit them for the needs of a subterranean life. Others are 

 amphibious and never occur at any great distance from water. At 

 least one member of the subfamily ^ is said to live among the branches 

 of trees. The food is chiefly vegetable, though most species occasion- 

 ally eat animal food. The vegetable food consists principally of grass 

 stems, though roots, bark, leaves, seeds, and fruit are at times eaten in 

 varying quantities. As voles are readily caught in traps baited with 

 meat, it is probable that flesh forms part of their normal food. Mollusks 

 are eaten freely when they can be obtained. 



The voles and lemmings breed very rapidly during the warmer part of 

 the year. The number of young in a litter varies from one or two to ten. 

 Five is, perhaps, the average number in the majority of species, though 

 it is x)robably less in those in which the females have only four mamm?e. 



^ PTienacomys longicauda True, from Oregon. In the original description of the 

 species (Proc. U. S. Nat. Mus., XIII, pp. 303-304, Nov. 15, 1890) Mr. True quotes as 

 follows from a letter from Mr. Anrelius Todd, who collected the type sj)ecimen: ''It 

 lives exclusively, as far as I have been able to ascertain, among the boughs and 

 branches of the Oregon pine trees (Abies douglasi), making a nest of a size smaller 

 than a robin's nest. It is usually situated on the upper side of a medium-sized 

 branch, perhaps 6 inches in diameter, and is composed of the leaves of the tree 

 deftly split in two from one end to the other and dried. The uest is neatly and 

 rather ingeniously made, and the sameness of the material is a novelty. * * * 

 The mouse is almost exclusively arboreal in its habits, but I think that I have reason 

 to believe that they sometimes come to the ground for food, as I have seen tracks in 

 the snow around the trees which I think vrere made by these little animals. They 

 could be tracked up and down the tree, but to no great distance from it, and were 

 most likely in search of food." 



