A fourth habitat is the marsh. In it there is here included the sphagnum bogs and marshy shores of lakes and streams. This habitat is characterized by damp ground, standing water, and dense vegetation. Typical mammalian species include the water shrew (Sorex bendirii), Townsend meadow mouse, muskrat and mink.
Other habitats, such as aerial for the bats and aquatic for the beaver and otter, might be listed.
The Arid Timbered Subdivision of the Transition Life-zone
In Washington the Arid timbered subdivision of the Transition Life-zone is the open, pine forest. Because of the aridity of this habitat, marshes and streamside thickets are uncommon, but where habitats of this kind do occur they have a fauna distinct from that of other habitats.
The pine forest habitat includes many diurnal species, such as the red squirrel, yellow-pine chipmunk, and Columbian ground squirrel. The white-tailed deer occurs here and, for most of the year, the mule deer. Snowshoe rabbits are usually present. Near rocks the bushy-tailed wood rat is common. Mice are scarce, probably because of the open nature of the surface of the ground. A night's trapping usually yields only a few Peromyscus maniculatus.
The mammalian fauna of the marshes and streamside thickets is similar. Shrews including Sorex vagrans and Sorex obscurus are uncommon. Meadow mice, including Microtus pennsylvanicus, Microtus longicaudus, and more rarely Microtus montanus, are taken.
The Arid Grasslands Subdivision of the Transition Life-zone
This subdivision is so much utilized by man where it occupies any considerable areas, and is of such a transitional nature elsewhere, that it is important for only a few native wild mammals. The sagebrush vole (Lagurus curtatus) seems to be confined to the arid grasslands. The white-tailed jack rabbit is now found principally in the arid grasslands, but its confinement there has resulted probably from competition with the black-tailed jack rabbit. The montane meadow mouse (Microtus montanus) is the only common, representative species. Many species from the Upper Sonoran Life-zone extend into the arid grasslands where conditions are suitable. These include Reithrodontomys megalotis, Perognathus parvus, Citellus washingtoni and Marmota flaviventris. A few species more typical of the Arid timbered subdivision of the Transition Life-zone stray onto the arid grasslands. Citellus columbianus and Microtus longicaudus may be included here.
The Upper Sonoran Life-zone
The sagebrush desert in Washington is relatively uniform in nature. Several different habitats may be distinguished, such as sandy areas, open sage, dense sage, stony ground, and talus. Qualitatively, however, the mammalian fauna of these areas is surprisingly similar. Quantitatively, there are great differences. For example, the grasshopper mouse is rare in the open sage areas with hard, claylike soil but common on drifted sand. The harvest mouse is common in dense sage but rare in open sage or in open, sandy areas. Mammals are abundant on the sagebrush desert and typical species include: the black-tailed jack rabbit, Nuttall cottontail, Ord kangaroo rat, Great Basin pocket mouse, Townsend ground squirrel, Washington ground squirrel.