80 RODENTS OP IOWA 



places of refuge. The meadow mouse is often seen in daytime, and 

 is not so nocturnal in its habits as are many of the related forms. It 

 is especially active in the evening and early morning. 



The nest is usually constructed in burrows 1 which follow along 

 under clumps of grass above the surface of the damp ground. It 

 is made up of grass or strips of weeds, coarser materials being used 

 on the outside and finer stuff within. Each nest has a small en- 

 trance hole near the bottom from which run two or more trails. 

 One of these often leads to an underground tunnel opening some dis- 

 tance from the nest. Nests in which the young are born are usually 

 lined with some soft material such as the "cotton" from the milk 

 weed or "cat-tail." Such nests are ordinariy placed in under- 

 ground burrows. If a nest is destroyed a new site is immediately 

 chosen, fresh materials are secured, and another domicile con- 

 structed often in a single night. When the home is disturbed the 

 occupants rush about without much idea of where they are going, 

 and are as likely to go towards the source of danger as away from it. 

 Apparently their eyesight is not good in the sunlight. If a way of 

 escape is not evident, they will put up a fight with claws and teeth. 



Ordinarily two, in some cases three litters of young are produced 

 in a season, the number in a litter ranging from four to eight with 

 six the average number. * The young are born blind and hairless. 

 The breeding season extends over most of the year except midwinter. 

 D. E. Lantz says: "The common meadow mouse (M. pennsylvani- 

 cus) is one of the most prolific of the American species. If six 

 young, the average number, are produced at a birth, and four litters 

 in a season, and if no enemy or disease check the multiplication, the 

 increase would be appallingly great. A single pair and its progeny 

 would in five seasons amount to over 2,000,000. This calculation is 

 conservative being based on the- theory that the young of one sea- 

 son do not breed until the next year an assumption that is likely 

 to be incorrect; for, the animals mature very quickly, and the 

 young born in spring probably breed in the fall of the same season. 

 If a thousand pairs of meadow mice survive a winter in any local- 

 ity, it is easy to understand how, after two or more seasons of unin- 

 terrupted increase, they might become a menace to agricultural in- 

 terests." 14 



Dr. C. H. Merriam in discussing this species says: "In the be- 

 crinning of winter, when the ground is frozen for some distance be- 



14 Lantz, D. E., Meadow Mice in Relation to Agriculture: Yearbook, U. S. 

 Dept. AgT., 367, 1905. 



