Rocky Mountain Jumping Mouse 63 
edges of woods, and in shrubby fields, and show a preference 
for moist ground. They build nests of grass, sometimes un- 
der ground, and sometimes on the surface in the grass or 
small bushes. Preble says that in late summer they build a 
globular nest of grass above ground, and that this is usually 
inhabited by two individuals, presumably a pair. This is 
FIG. 23. ROCKY MOUNTAIN JUMPING MOUSE, ZapUS pHncepS 
Skull, showing dentition, x 4 nearly 
after the close of the breeding season. The breeding season 
is in May or June, and five or six young are born. Litters 
of young have, however, been found in late September, 
showing that it may breed through the summer. The food 
is seeds and other vegetable matter. 
Jumping Mice hibernate, but may in mild weather come 
out for a short time. The hibernation takes place in holes 
under ground. 
Zapus princeps (Lat., chief). Rocky Mountain Jumping 
Mouse. 
Zapus princeps Allen, BttU. Am. Mtis. N . H., v., p. 71 (1893). 
