Osgood (1909:149) recorded the subspecies P. b. attwateri from Cedar Vale, Chautauqua County, Kansas, but the specimen from there must now be assigned to cansensis on geographic grounds. Probably the specimen was not obtained from Cedar Vale itself for the habitat is not suitable there. Numerous specimens are known from 3 mi. W Cedar Vale, in Cowley County, Kansas, all of which are assigned to cansensis. Osgood's recorded locality is situated between this locality and the type locality of cansensis, which is 4 mi. E Sedan, Chautauqua County, Kansas. The distribution of cansensis also is shown in Fig. 1.
Fig. 1. Distribution of the brush mouse in Kansas. The southernmost row of counties includes from left to right Cowley, Chautauqua, Montgomery, Labette, and Cherokee. Black dots represent trapping localities from which brush mice were not obtained. Triangles represent localities from which brush mice were obtained. The stippled area contains suitable habitat for the brush mouse, but was not investigated. The easternmost triangle represents a place 2 mi. S Galena, Cherokee Co., Kansas, from which P. b. attwateri is known. The westernmost triangle represents a place 3 mi. W Cedar Vale, in Cowley Co., Kansas, from which P. b. cansensis is known. The triangle of intermediate position represents the type locality of P. b. cansensis, a place 4 mi. E Sedan, Chautauqua Co., Kansas. Many of the trapping localities have been investigated more than once.
The probable geographic range of P. boylii is based on trapping data (see Fig. 1). The brush mouse is confined to systems of wooded cliffs in Kansas. The two subspecies seem to be separated by more than 80 miles of grasslands. Blair (1959) has postulated that in the northeastern part of its range P. b. attwateri is represented by disjunct, relict populations formed by diminishing montane or cool, moist environmental conditions. He has implied that the critical climatic change occurred during post-Wisconsin times, and that the isolation of these populations occurred so recently that no morphological differentiation has resulted in them. Inasmuch as the species is widely distributed in México, the southwestern United States, and in California, and has been recorded from the Pleistocene of California (Hay, 1927:323), it is reasonable to suppose that the species immigrated into Kansas from the southwest and that the immigration was in a generally northward or eastward direction. If long tail and large eyes are specializations for a scansorial mode of life (discussed below), then P. b. cansensis must be considered more primitive than P. b. attwateri for the eyes are less protuberant and the tail is shorter in P. b. cansensis than in the latter. I suggest that P. b. cansensis occurred in what is now known as Kansas before P. b. attwateri entered this area by way of the Ozark Mountains. The occurrence of a mouse of "the truei or boylei group" (Hibbard, 1955:213) in southwestern Kansas in the Jinglebob interglacial fauna of the Pleistocene adds little to support the thesis outlined above, but is not inconsistent with the thesis. Incidentally, the geographic distribution of P. boylii may differ somewhat from that shown by Blair (1959:fig. 5); whereas he has mapped the distribution of P. boylii to show disjunctivity in P. b. attwateri and homogeneity in the distribution of other subspecies of the brush mouse to the westward and southward, disjunctivity actually occurs frequently also in the western and southern subspecies.
Ecology
In Kansas the brush mouse is confined to systems of cliffs, the faces of which range in height to at least 40 feet. The highest cliffs—some approximately 100 feet—on which brush mice are known to occur in Kansas are along Shoal Creek, Cherokee County. The brush mouse is found on low bluffs that are parts of higher systems, but in Cherokee County the mouse was not obtained from low bluffs separated by even a few miles from the cliff-system along Shoal Creek. As implied above the brush mouse is adapted for a scansorial mode of life; but other mice and rats inhabit the rocky crevices of low bluffs. Whereas the brush mouse is well adapted for living on high cliffs it seems that the other rodents are better adapted for life on low cliffs. Sigmodon hispidus was obtained from the low, limestone cliffs mentioned previously. From most low bluffs in southeastern Kansas (and on some high bluffs outside the geographic range of cansensis) Peromyscus leucopus was obtained. In Cowley County the brush mouse was abundant when P. leucopus was not and vice versa during this study. Sigmodon hispidus did not associate with the brush mouse in any area, although S. hispidus was often trapped in grassy areas adjacent to cliffs and on the grassy crests of the hills. Except at the locality in Cherokee County, the pack rat, Neotoma floridana, was found in association with the brush mouse. Microtus ochrogaster was the must abundant rodent in adjacent southwestern Missouri (Jackson, 1907) before Sigmodon thoroughly infiltrated this area and southeastern Kansas. Activities of other rodents may have confined the brush mouse ecologically to cliffs. Although the grasslands are a barrier to further intrusion by the brush mouse into Kansas, one cannot assume that they alone confined the brush mouse to cliffs. Such an assumption would not explain its absence on systems of cliffs similar to and near other systems of cliffs on which it is found in the non-grassy Ozarkian habitats of Arkansas, as was noticed by Black (1937). Such an assumption would not indicate why the size of the cliff-systems is correlated with the absence or presence of the brush mouse on the northeastern margin of its geographic range.
Parasites found on P. b. attwateri include three individuals of the laelapid mite, Haemolaelaps glasgowi. Two of these mites were removed from a live mouse. Two larval Ixodid ticks, Ixodes possibly cookei, were removed from the pinnae of the ears of a specimen of cansensis from the type locality, 4 mi. E Sedan, Chautauqua County. Four larval Ixodid ticks, Dermacentor possibly variabilis, were removed from the pinnae of the ears of a live specimen of cansensis from 3 mi. W Cedar Vale, in Cowley County.
Table 2. Stomach Contents of 38 Brush Mice from Southeastern Kansas in Winter and Spring.
| Localities and number of stomachs | Month | Empty | Acorn pulp | Seeds | |
| 2 mi. S Galena | |||||
| 10 | May, 1959 | 2 | 6 | 2 | |
| 11 | December, 1959 | 1 | 10 | 0 | |
| 3 | March, 1960 | 1 | 2 | 0 | |
| 4 mi. E Sedan | |||||
| 3 | December, 1959 | 3 | 0 | 0 | |
| 2 | April, 1961 | 1 | 1 | 0 | |
| 3 mi. W Cedar Vale | |||||
| 6 | December, 1959 | 1 | 3 | 2 | |
| 3 | December, 1960 | 0 | 3[B] | 0 | |
[B] Judged to be acorn pulp or hickory nut pulp.