During the latter part of the 1941 season, an investigation was made of the mammalian fauna along the East Entrance highway from the park boundary to the south-east margin of Dutton Ridge. Both sides of the highway were set with live traps for a distance of a little over three miles. Only small mammals can enter these traps of these four species were represented: Klamath chipmunk (Eutamias amoenus amoenus), Sierra least weasel (Mustela cicoquanii muricus), Gambel's deer mouse (Peromyscus maniculatus gambelii) and Coues' pocket mouse (Perognathus parvus mollipilosus). This last species had not previously been reported from Crater Lake National Park or any part of Oregon north of Fort Klamath. It is associated with relatively arid territory of north-east California and its presence in a forest-covered region within the park boundary is of interest. The deer mice taken along the rims of Wheeler and Sand Creek canyons are in type more like the Sonoran deer mouse than deer mice taken elsewhere in the park.

Coues' Pocket Mouse: Three female Perognathus were taken along the rim of Wheeler Creek canyon. One, the largest was lactating and also pregnant. It contained six embryos four in one uterine horn and two in the other. One female was pregnant only and contained for embryos two in each horn. The smallest female was neither lactating nor pregnant and may not be within the limits of adult size. The measurements in millimeters are as follows:

From the measurements it may be seen that these mice are small bodied and long tailed with relatively large feet and small ears. All these mice are smaller than the species' average recorded by Vernon Bailey for the state but the beginning of at least a second brood in one female would make it seem probable that she was fully adult.

Gambel's Deer Mice: Twelve deer mice were taken along the highway between the East Entrance and the Lost Creek Ranger Station. Seven, of which six were females, proved to have a body length of 85.0 mm or more and may be considered adult enough for statistical purposes. Most of them were young adults so the average body length is small. Fourteen mice were taken on Dutton Ridge along the East Entrance highway. Ten of these proved to have a body length of 85.0 mm or more. This group was also composed of young adults. The data follows:

All means are below 90.0 mm the usual figure for large samples of Peromyscus including older mice.

It may bee seen that mice from the southeastern side of the park have considerably shorter tails than mice taken elsewhere. The fact that they are rather small mice minimizes the differences for smaller Peromyscus have relatively longer tails than larger ones.

The differences between the rim and east entrance samples is 8.9 +/- 2.08 per cent and therefore more than four times its standard error. The difference in tail percentage between the Rim sample and the combined Dutton Ridge and east entrance sample of 17 mice is 7.4 +/- 1.37 percent. This difference is more than five times its standard error. Smaller differences are present between mice from the east and south portions of the park in tail percentages but they are still more than twice their standard errors and so of statistical significance.

A tail percentage of just over 80 is more typical of the interior valleys of California than of any forested part of Oregon and this situation emphasizes the effect upon small mammals which the pumiceous character of the soil and sparse vegetation seem to be producing.

The mean ear size of these mice is slightly below that of the Rim area, 17.5 +/- .09. Since the ear length is greater in larger mice the difference in body size between the Rim 90.09 +/- .38 and the eastern series may very well be the factor involved. The differences are not statistically significant.

Foot length: Since foot length must be computed separately in each sex that of the females in the combined East Entrance-Dutton Ridge series is the only one presented:

This mean is smaller than that of the Rim or South Entrance series both differences being statistically significant. For females the Rim foot length is 20.7 +/- .08 and South Entrance 20.6 +/- .15. Whether the difference in body size is the only factor is more doubtful in this case.

Summary

1. Coues' pocket mice were present and breeding along the East Entrance highway of Crater Lake National Park in 1941. These mice are at home in arid regions.
2. Gambel's deer mice taken from this region have a relative tail length typical of mice from the interior valleys of California.
3. It is suggested that the sparsity of vegetation in this region is an important factor in these distributional arrangements.