248 



MAMMALS OF AMERICA 



y-et they are so compact that the animals pass 

 the coldest weather snugly housed in them under 

 the snow. Trails, often of great length and 

 worn smooth by constant use, lead to neighbor- 

 ing feeding grounds. 



While most surface nests are for shelter only, 

 sometimes the young, especially of swamp 

 species, are produced in them. However, the 

 young of most kinds are born in underground 

 nests and are rarely seen unless uncovered by 

 accident. They are at first hairless and blind. 



" The common Meadow Mouse of the United 

 States is one of the most prolific of our species," 

 says Lantz. " Estimating the normal increase 

 at six young, with four litters in a season, and 

 assuming that there were no checks upon the 

 increase, the results are appalling. A single pair 

 and their progeny in five seasons would amount 



has been calculated at from twenty-four to 

 thirty-six pounds. \\'hen one considers in con- 

 nection with this estimate the great numbers of 

 these animals in our meadows, swamps, and 

 forests, the total quantity of food consumed by 

 them appears so enormous as apparently to 

 exceed the productive capacity of the soil. A 

 thousand Meadow Mice in a meadow would re- 

 quire at least twelve tons of grass or other vege- 

 tation to maintain them for a year." 



They are not especially partial to seeds, but 

 flesh in any form is acceptable to them. They 

 do not usually lay up food for the winter ; but 

 one Alaskan species has been seen to store roots. 

 Certain peculiarities of habits are common to 

 most of the species. " None are known to hi- 

 bernate," says Vernon Bailey, " but in the north 

 thev have snug winter homes under the snow, 



From a drawing by the U. S. Biological Survey 



MEADOW MOUSE RUNWAY 



An ingenious arrangement of branching tunnels made by the little animal both 

 in search of food, and to provide an easy means of escape 



to nearly 1.000,000 individuals. This calculation 

 is under mark, since it is based on the assump- 

 tion that the young do not breed tmtil about a 

 year old. The animals, however, mature very 

 rapidly and the spring young undoubtedly breed 

 in the fall of the same year. 



" In summer the principal food of these Mice 

 is green vegetation and unripe seeds of grain 

 and grasses. As the season advances, ripe grain 

 and seeds take the place of the immature : and 

 in winter bulbous and other roots are in part 

 substituted for stems and leaves. When con- 

 venient, and green vegetation is lacking, the 

 bark of trees and shrubs becomes a staple food. 

 It is mainly in winter that the apple orchards 

 and yoimg forest trees suffer from attacks of 

 Mice. 



" The quantity of green vegetation eaten by a 

 single adult Field Mouse in the course of a year 



where they move about freely in numberless 

 tunnels. They burrow in the ground, and are 

 famous for their little roads or smooth trails 

 which run through the grass from burrow to 

 burrow or away to their feeding grounds." 



There seems to be no definite breeding season : 

 nests with young in them have been found at 

 all seasons of the year. Four to eight at a birth 

 is the usual number. As the period of gesta- 

 tion is only about twenty days, and in temper- 

 ate latitudes from fotu- to six litters a year are 

 produced, it will be seen that the annual increase 

 must be enormous. The economic status of the 

 Meadow Mouse is indeed a very important one ; 

 it has been carefully estimated that the. Mice of 

 the genus Microtus alone cause an average 

 annual damage to the American farmer of at 

 least $3,000,000. As Bailey says : " Too small 

 and too numerous to be successfullv destroyed 



