16 
AN ECONOMIC STUDY OF FTELD MICE. 
coarser materials outside, but compact and of finer stun 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 >orts 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. — Xests. burrows, and trails of Microtus pennsylvanicus. a, Surface trails: b, 
opening to burrows : c, underground tunnels: n, surface nest: it', underground nest. 
suspected from any surface indications. Under the favoring shelter 
of piles of weed>. 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 weed-. 
The rapidity with which meadow mice work is surprising. If the 
nest is destroyed 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 danger as away from it. 
When cornered, they stand on their haunches and defend themselves 
