) show
acorns to be the most commonly used food in winter and spring. Seed
coats were only rarely found, and insects were absent. Two captive
females preferred acorns. Live beetles and grasshoppers of numerous
kinds were decapitated and their inner parts eaten. Seeds (wheat, corn,
and oats) were also eaten. Inasmuch as acorns appear to be the chief
food, it is not surprising that the brush mouse is usually found on
cliffs that support stands of blackjack oak (_Quercus marilandica_).
Other oaks are present, but I have no evidence that the brush mouse eats
their acorns. A. Metcalf told me that he observed in December, 1960, a
released brush mouse interrupt its movement toward a hole in a
cliff-face along Cedar Creek, Cowley County, in order to pick up an
acorn (judged to be from the blackjack oak) in daylight. The mouse
carried the acorn into the hole in the cliff. I have observed that
captive brush mice eat acorns of the blackjack oak but not some other
kinds of acorns.

_Behavior_

The chief differences observed between the brush mouse and other species
of the genus _Peromyscus_ in Kansas can be summarized as follows: the
brush mouse is a superior and more cautious climber; seldom jumps from
high places when under stress; is capable of finding its way better in
partial darkness; has a stronger preference for acorns; and sometimes
buries or hides seeds or acorns. These are all behavioral adaptations
that seem in harmony with its mode of life.

Buck, Tolman, and Tolman (1925) showed the balancing function of the
tail in _Mus musculus_. Climbers (for example, squirrels) often possess
long, well-haired tails. It is reasonable to suggest (as did Hall,
1955:134) that the long, tufted tail is an adaptation for a scansorial
existence. Little observation is necessary to observe how such a tail is
used in balancing. Furthermore, it is used as a prop when the mouse is
climbing a vertical surface. Dalquest (1955:144) mentioned tree-climbing
in _P. boylii_ from San Luis Potosi, Mexico. It may occur in _P. b.
attwateri_ or in _P. b. cansensis_ also, but there is no evidence as yet
to prove it.

The brush mouse can seldom be induced to jump from heights of two feet
or more. Rather it tends to scamper downward or to remain in place. It
often swings itself over an edge, holding to it by its hind feet, and
sometimes to it lightly with its tail, and reduces a short jump by
almost the length of its body. Such caution seems to be an