id="Page_107" class="x-ebookmaker-pageno" title="[Pg 107]"/> 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 adaptation in a mouse that lives as a climber.

Many animals of cavernous habitats have small eyes (see Dobzhansky, 1951:284). Some nocturnal animals (for example, owls) have large eyes. The brush mouse has large, protuberant eyes; it lives in the deep crevices and fissures of the cliffs on which it is found, but it is not strictly a cave-dwelling animal. Perhaps large eyes aid the brush mouse in performing activities in the partial darkness of a deep crevice or hole in a cliff. Brush mice experimentally placed in what appeared to be total darkness fed, built houses of cotton, and ran and climbed in the usual manner.

On several occasions the captive brush mice hid surplus seeds and on other occasions hid acorns by burying them and sometimes by placing them in a small jar. The mice never carried the surplus food into their house.

Black (1937:195) has claimed that the brush mouse builds a nest similar to that of the nest of the pack rat, Neotoma floridana. Hall (1955:134) doubts this to be the case. Dalquest (1953:144) described a nest of P. boylii from San Luis Potosí as seven inches in diameter, made of leaves, and found in a hollow tree. Drake (1958:110) noted that P. b. rowleyi lives in holes and crevices in rocky bluffs in Durango, México. I have found this to be the case for P. b. attwateri, as did A. Metcalf (unpublished) for P. b. cansensis. Nests of sticks and leaves were taken apart by Metcalf, and all sign indicated only the presence of the pack rat. I have observed that there are no such houses on the cliffs along Shoal Creek, Cherokee County, and that no pack rats have been obtained from there (pack rats have not been reported from Cherokee County). Blair (1938) found two brush mice (P. b. attwateri) in the house of a pack rat in Oklahoma. Nests of the brush mice that occur in Kansas have not been found.

A lactating, pregnant female (KU 81833) of P. b. attwateri, containing three embryos, was obtained on December 24, 1959, and shows that this subspecies breeds in winter. Accumulated records for the subspecies indicates year-round breeding (see Cockrum, 1952:181). Another female obtained on March 27, 1960, was probably lactating.

Pregnant females of P. b. cansensis (KU 84892, 84895, and 84890) were obtained from the type locality on April 1-2, 1961, containing 3, 4, and 5 embryos respectively. This indicates, perhaps, increased breeding in spring; five was the highest number of embryos found in brush mice in Kansas.

In the period of my study the populations of brush mice became smaller, perhaps owing to the severe winter of 1959-1960. In Cowley County, P. leucopus is now abundant and P. boylii rare where in December of 1959, the opposite was true. It is also possible, of course, that trapping has depleted the populations.