16 



AN ECONOMIC STUDY OP FIELD MICE. 



coarser materials outside, but compact and of finer stuff within, each 

 having a small opening on the side near the bottom. From this 

 opening two or more trails diverge, one usually leading into an 

 underground tunnel which opens at some distance from the nest. 

 Nests intended to receive the young are lined with the softest of 

 accessible materials, often with pappus of milkweed {Asclepias) or 

 cat-tails (Typha). Such nests are sometimes hidden under grass, 

 brush, or other litter, but more frequently are placed in underground 

 burrows. The normal number of young varies from four to eight, 

 the average being about six. 



The trails of meadow mice are interesting subjects for study. The 

 animals take advantage of all sorts of shelter, especially that which 

 is close to the ground. Under fallen leaves and weeds the trails 

 become half tunnels. Even in the open meadow they are often 

 entirely hidden under old grass, and their presence would hardly be 



Fig. 1. — Nests, burrows, and trails of Microtus pennsylvanicus. a, Surface trails ; h, 

 opening to burrows ; c, underground tunnels ; n, surface nest ; n', underground nest. 



suspected from .any surface indications. Under the favoring shelter 

 of piles of weeds, grass, or other litter the trails made by the ani- 

 mals are usually more intricate than elsewhere. The accompanying 

 sketch (fig. 1) was made from trails and nests uncovered by removing 

 a pile of weeds. 



The rapidity with which meadow mice work is surprising. If the 

 nest is destroj T ed they choose a new site and construct a new nest of 

 fresh materials in a single night. They work both night and day, 

 but are especially active in the evening and early morning. They are 

 less active in the middle of the day, especially in sunlight. 



When disturbed in their homes meadow mice rush about with great 

 celerity ; but in sunlight especially they do not see well, and are almost 

 as liable to rush blindly toward the point of clanger as away from it. 

 When cornered, they stand on their haunches and defend themselves 



