130 The Mammals of Colorado 
however, they are either driven out, or before whose advent 
they retreat. They Hve in holes among the rocks and in or 
under logs, and in the ground; in fact, they make themselves 
at home anywhere. Sometimes they build nests under boards 
that may happen to be lying on the ground, but I have 
never known them to utilize an old bird's nest in the manner 
that an eastern deer -mouse does. Such nests as I have seen 
in various locations have been made of soft materials of some 
kind, often fine dry grass, usually made into a globular form 
with a cavity in the centre. Their food consists of seeds and 
grains of any kind, insects, and they will eat each other 
when caught in traps. Stone and Cram, in American 
Animals, state that they are "great lovers of fresh meat and 
have often been caught in the act of devouring both eggs and 
young birds." In the regions where the cedars or junipers 
abound they seem to eat many of the berries of these trees, 
and doubtless many pifion nuts. 
The Deer -mice are practically strictly nocturnal in their 
habits, and the collector's traps will remain untouched in the 
daylight hours, in a locality where they abound, and w^here 
the morning's visit to the traps will find a good catch of the 
pretty little fellows. Often they are so abundant that 
several days' trapping has to be done to thin them out so 
as to give the less plentiful and more desirable mammals a 
chance at the traps. 
The Deer -mice do not hibernate, though in the very coldest, 
or in stormy weather, they may remain quiet for a day or two, 
but as soon as it moderates they begin to stir about again. 
It is at the approach of winter that they are most common 
about houses, as then they seek the shelter afforded by the 
buildings. 
Deer -mice breed in spring and summer, and have from 
four to eight young in a litter, six being probably the average 
number. 
