448 MURIDAZ—AGRESTIS 
colony, lying partly above and partly below ground. | They 
weave loose nests of grass for the reception of their young. 
In winter or early spring these nurseries are more frequently 
placed under ground or in sheltered places under logs or piles 
of wood ; they are then sometimes lined with warmer materials 
such as fur and wool. In summer they are usually on the sur- 
face, invariably composed of grass, and are often very evident 
in hayfields by clogging the knives of the reaping machines. 

Fic. 70.—HORIZONTAL SECTION OF RUN OF Grass MOUSE PASSING UNDER A LOG. 
From a sketch by L. E. Adams; scale 1o feet. 

Fic. 71.—PLAN OF RUNS OF GRASS MICE IN COARSE GRASS, partially above and partially 
(where blackened) below ground. From a sketch by L. E. Adams; scale 12 feet. 
These mice are very hardy and never hibernate, although 
they may be comparatively inactive in cold, damp weather. In 
winter they often seek more sheltered habitats than the open 
fields, and have been caught occasionally in cellars and out- 
houses; but never -habitually resort to ricks and granaries. 
Like other small mammals, they probably suffer more from 
hard “black” snowless frosts and summer droughts than from 
snow, which makes the work of burrowing actually easier and 
protects both vegetation and mice from the cold. In captivity 
the male may safely be left with his own wife and children, 
though he will devour strange litters, which suggests that the 
' For the habits of “voles” in times of snow, see C. Hart Merriam, Mammals of 
Adirondacks, 11, 124. 
