SPECULATION AS TO THE LATER DISTRIBUTIONAL HISTORY OF THE MAMMALS

Whereas it is probable that a few of the species now occurring in Washington evolved there, most are immigrants from other areas. The success of a given species in any area is dependent on numerous factors which may be classified under food, shelter from the elements, protection from enemies and safe breeding places. The factors may be of an inorganic nature, such as climate, soil and exposure or they may be organic, such as vegetation, competition for food and response to enemies. Abundance results in population pressure and a tendency for the range of a species to expand.

Mammalian populations are dynamic and change in accordance with alterations in environment. Because the later geologic history of the state of Washington was violent, with resultant changes in climate and geography, the mammalian populations and the distribution of the species have changed much. With changes in environment, rare species may become common; common and widespread species may become rare or extinct; species foreign to the area may enter, become established and affect the distribution of other forms.

Subspecies are groups of individuals with similar genetic components or are groups of microgeographic races. In instances where the phenotypic expression of these similar genetic factors, or the "characters," are, as a unit, uniformly different from those of animals of the same species in another geographic area, it is convenient to give recognition to the two kinds by separate subspecific name. Intergradation between two geographically adjacent subspecies occurs, directly or where impassable barriers separate them, indirectly by way of one or more other subspecies. Subspecies of mammals are geographic races, which means that to warrant recognition by subspecific name, there must be a logical geographic range in addition to morphological characters.

Timofeef-Ressovsky (1932, 1940) advances the theory of harmoniously stabilized gene-complexes to account for the persistence of subspecies. The persistence of subspecies as genetic units has been best explained, I feel, by Sumner (1932: 84-86) who theorizes as follows:

1. The number of young produced by a subspecies is greater than the carrying capacity of the land they occupy, at least at certain times or in some years.

2. Population pressure results, with a tendency of individuals to emigrate outwards, to the border of the range of the subspecies, where the population pressure is less.

3. The outward moving tendency keeps the center of the range of the subspecies genetically "pure."

4. The peripheral wave continues, as long as favorable habitat is encountered, until an oppositely directed wave of another race is encountered.

5. Areas of intergradation represent local mingling of genetic factors and do not affect the "pure" individuals of the central part of the range of the subspecies.

Certain aspects of this hypothesis are strongly supported by the distribution of mammals in Washington. Witness the rapid invasion of Citellus beecheyi and Lepus californicus in Washington, and the eastern cottontail in western Washington and the domestic rabbit in the San Juan Islands. The volume of the "wave of population pressure" where no opposing force is met, is scarcely believable. In seven years the eastern cottontails released in southwestern Washington multiplied from a maximum of 12 individuals to a minimum of 40,000.

Competition between subspecies where their ranges come into contact seems to be exceptional. Peromyscus maniculatus oreas and P. m. austerus seem to afford an example of this. However, in a few cases subspecies seem to be determined in part by adaptation to restricted environments; each race lives only where local conditions favor its respective adaptations.

In the pocket gophers, where restricted habitat and fossorial habits cause numerous microgeographic races, these microgeographic races may be potential subspecies. This is especially true in the Puget Sound area, where six races occur in a small area. These races meet all the requirements of subspecies and are recognized as such. It should be pointed out, however, that these races and probably many other races produced by isolation, may represent degenerative mutations of the type mentioned by Wright (in Huxley, 1940). The principal differences of such races seem to have resulted from the loss of factors of original multiple factor series, with resultant homogeneity of the race. Inherent variability is another thing that has to be taken into account when considering the differentiation of the mammals of Washington into subspecies. The pocket gopher is an extremely plastic species, especially in Washington, whereas the Douglas squirrel is less so. The flying squirrels, the yellow-pine chipmunk and the snowshoe rabbit are the other plastic species. These species are not so likely to break up into numerous subspecies over all of their ranges as they are in Washington where in a small area the topography is highly varied. The range of the one subspecies, Tamias amoenus amoenus, to the southeast of Washington is larger than the combined ranges of all six races occurring in Washington but, so far as I can see, the topography and environment are no more varied in Washington than in the mentioned area to the southeast of it. The range of one subspecies, Lepus americanus americanus, in Canada is several times larger than the entire state of Washington, in which four races are found.

The shrews are poor subjects for a study of differentiation, principally because their small size makes it difficult to see morphological variations that may be present. The difficulty is increased because cranial sutures become ossified at an early age. Although it is difficult to evaluate the differentiation in them, there is some. The bats, especially the Myotis, are less restricted by geographic barriers than are terrestial mammals. Nevertheless, obvious differentiation exists. The larger predatory mammals and the artiodactyls are able to move over large areas, at least in the breeding season, but in these animals also, some differentiation has occurred.

The greatest changes, other than the extinctions, to occur in the mammalian fauna of Washington since the late Pleistocene, are changes in distribution. The interglacial cycle preceding the Vashon-Wisconsin glaciation was of far greater duration than the Recent. Presumably the mammalian fauna had, from a distributional standpoint, reached a relatively stable condition. The descent of the Vashon-Wisconsin ice destroyed the stability and set parts of the fauna in motion. Probably no stability was reached before the ice began to recede, and when it did so the previous movements of the various species were, at least in part, reversed. Stability has not yet been reached by the mammalian fauna of Washington. Great changes have occurred in historic times and other changes probably are under way at present.

In the following pages an attempt has been made to interpret the probable late Pleistocene and Recent distributional history of the species of mammals occurring in Washington. The interpretations are made in the light of what is known of the physical history of the state and are to be accepted as such rather than as evidence for the conclusions made concerning the physical history of the state of Washington and adjacent areas.

Scapanus townsendii.—Probably this animal was confined to the Humid Transition Life-zone of the Pacific Coast since the Pliocene.

Scapanus orarius.—This species probably had a history similar to that of townsendii up to the late Pleistocene. It seems slightly more adaptable than townsendii, and to be able to extend higher into the mountains. The distribution of the subspecies orarius is almost exactly that of S. townsendii. In Oregon, orarius extended eastward over the Cascades where the subspecies schefferi developed. Perhaps this subspecies developed since the Pleistocene and since that time extended along the Columbia River Valley to southeastern Washington. The race yakimensis, in the Yakima Valley area, is closely related to schefferi, and seemingly could have been developed from a stock of schefferi that migrated westward across the Simcoe Bridge.

Neurotrichus gibbsii.—The history of Neurotrichus in North America was probably similar to that of the two species of Scapanus. It tolerates environmental differences to about the same degree that Scapanus orarius does but occurs much farther south (Monterey County, California) than S. orarius. This may be because Neurotrichus has no counterpart to compete with it in the south, whereas Scapanus orarius must compete in northern California with the morphologically similar Scapanus latimanus. S. orarius stops short at this place and S. latimanus occupies all the territory to the south.

The shrew-mole of the lowland of Washington (N. g. minor) probably became distinct from the mountain subspecies (gibbsii) in Vashon-Wisconsin time.

Sorex cinereus.—It is reasonable to suppose that the cinereous shrew had a continuous range across the forested area of British Columbia in pre-Wisconsin time. Without having been isolated, the dark coastal race (streatori) may have developed from the wider-ranging inland cinereus, as a response to the denser, humid, coastal forest-habitat, after having been forced southward to Washington by the Vashon Glaciation. Since that time it is presumed to have reoccupied the coast of British Columbia and southern Alaska. This coastal race might have developed in Vashon time, while isolated in southwestern Washington. The Cascades are populated by a race of the Rocky Mountain Fauna, S. c. cinereus, which probably entered the Cascades from northeastern Washington or British Columbia in Recent Time. The absence of the species in western Oregon, its rarity in western Washington, and its abundance farther north suggest a northern origin and northward rather than southward postglacial movement. Had the full species cinereus been a preglacial resident of western Washington we would expect streatori or a race related to it to occur in the Cascades.

Sorex merriami.—The periphery of the range of this member of the Great Basin Fauna may have been in southeastern Washington since pre-Wisconsin time.

Sorex trowbridgii.—This shrew is a typical Pacific coastal species with an extensive range along the Pacific Coast south of Washington. The Washington population may have been isolated in southwestern Washington during Vashon time or may have crossed the Columbia into Washington from western Oregon early in the Recent. Since the retreat of the ice it has extended northward to southern British Columbia and eastward to the eastern side of the Cascades. Save for crossing the Cascades its postglacial movements have been slight, as is typical of Pacific Coastal species. The race destructioni probably has been isolated on Destruction Island for several thousand years.

Sorex vagrans.—This species probably has had a continuous range over the western United States since the late Pleistocene. The dark coastal race (vagrans) probably was differentiated from the paler races of the Great Basin in response to the more humid climate along the coast.

Sorex obscurus.—The history of this shrew of alpine predilection probably corresponded closely to that of Sorex cinereus. The derivation of the dark, long-tailed, coastal race (S. o. setosus) from the smaller, paler, inland race (obscurus) probably occurred before Vashon-Wisconsin Time. Sorex o. setosus is one of a complex of races distributed along the Pacific Coast from Alaska to California.

Sorex palustris.—This species has a wide range in North America and extends southward in the Cascade-Sierra Nevada Chain to southern California. Its extensive range at present in this mountain chain suggests that it was resident in the Cascades previous to Wisconsin time. Mountain water shrews probably reached the Olympic Mountains from the Cascades by way of the Puget Bridge in early Recent Time.

Sorex bendirii.—This Pacific Coastal species probably had a history very similar to that of Neurotrichus and Scapanus orarius.

The difference between the Bendire water shrews of western Washington and western Oregon indicates that the Washington population was separated from the shrews of western Oregon during Vashon Time. The white-bellied race of the Olympic Peninsula is probably of local origin.

Microsorex hoyi.—The Washington record of this shrew at Loon Lake, Stevens County, is in an area where mammals typical of the Rocky Mountain Fauna occur.

Myotis lucifugus.—The dark race of this species (alascensis) may have persisted through the glacial period in southwestern Washington. The race carissima, of the Great Basin Fauna, may have entered the state since the glacial period, from the south, of course. Habitat selection determines their range at present.

Myotis yumanensis.—The dark, coastal race (saturatus) seems to be an established member of the Pacific Coastal Fauna. Unlike lucifugus, the coastal race is not found east of the Cascades. The race sociabilis, of the Great Basin, has doubtless entered the desert of eastern Washington from eastern Oregon.

Myotis keenii.—The southernmost record station for this north coastal species is on the Olympic Peninsula of Washington. It probably developed in the humid, northern part of the Pacific Coastal area previous to the last Pleistocene glaciation and extended its range to the south in Vashon-Wisconsin Time. The range of tolerance in M. k. keenii seems to be more restricted than that of M. lucifugus alascensis.

Myotis evotis.—In Washington, the distribution of this bat is similar to that of Myotis lucifugus. The dark, forest race probably originated in the north-coastal region. The paler race, that developed in the southwest, entered eastern Washington from Oregon.

Myotis thysanodes.—In Washington this species has been recorded only in the southeastern part where the Great Basin Fauna occurs. It probably originated in the southwestern United States, and a point in British Columbia a little way north of Washington marks the northern edge of its natural range.

Myotis volans and Myotis californicus.—Remarks made about Myotis lucifugus apply also to these two species.

Myotis subulatus.—The northwestern periphery of the range of this species seems to be in eastern Washington.

Lasionycteris noctivagans.—Undifferentiated subspecifically from coast to coast, no basis is provided for judging the route by which this species entered the state.

Pipistrellus hesperus.—The northwestern periphery of the range of this bat, also, lies in eastern Washington.

Eptesicus fuscus.—Big brown bats from both eastern and western Washington seem to have been derived from the Pacific Coastal race of the species. Presumably it extended its range westward across the Cascades in early post-Pleistocene Time.

Lasiurus cinereus.—No speculation as to the distributional history of the hoary bat seems justified at present.

Corynorhinus rafinesquii.—The dark, coastal race of this bat probably persisted in southwestern Washington and western Oregon through Vashon Time and moved northward in the Recent. The paler intermedius probably invaded eastern Washington from eastern Oregon in the Recent.

Antrozous pallidus.—This species strays into eastern Washington from Oregon as part of the Great Basin Fauna.

Ursus americanus.—The dark, western race of the black bear (altifrontalis) and the paler, inland race (cinnamomum) were probably separated by a glacial divergence. The inland race has entered northeastern Washington in the Recent with other members of the Rocky Mountain Fauna.

Ursus chelan, etc.—The apparent past distribution of chelan indicates it to have invaded Washington from British Columbia since the Pleistocene.

The apparent absence of grizzly bears from the southern Cascades and western Washington may indicate their absence from these areas immediately before pre-Vashon time, or their extermination in or shortly after that period.

Procyon lotor.—The raccoon of western Washington seems to be the Pacific Coastal race which occurs also in western Oregon and northwestern California. This indicates that the coastal race (psora) was confined to the coastal area south of Washington during Vashon Time and has only recently reinvaded western Washington. It is possible, though less likely, that raccoons existed in southwestern Washington during Vashon Time but did not develop racial characters, or that the Columbia was crossed so frequently that genetic differences were dispersed throughout the entire population.

Reasons why the second hypothesis is inadequate are: (1) Raccoons range but little north of the state of Washington, both east and west of the Cascades. (2) Raccoons of western Washington and the area about San Francisco Bay, California, are as much alike as are raccoons from southwestern Washington and northwestern Oregon. It is thought that raccoons, if resident in western Washington since interglacial time, would have developed strong racial characters, and the fact that they have not indicates that they have entered the state at a relatively recent date.

The raccoon of eastern Washington (excelsus) is a member of the Great Basin Fauna and has probably included southeastern Washington in its natural range for a long period of time. The raccoon has not extended its normal range into northeastern Washington, although it is seemingly ideal raccoon habitat; only an occasional vagrant occurs there. A stock of raccoons from which emigrants might come has existed in southeastern Washington and the Yakima Valley for some time. The Columbia River might serve as a highway by which emigrants could reach northeastern Washington.

Martes caurina.—The earlier distributional history of the western marten has been postulated by Davis (1939: 131-132), who stated: "When the ancestral stock split into the two groups, the one that gave rise to americana may have pushed eastward across Canada to the Atlantic Coast; the other, giving rise to caurina, may have migrated southward along the Sierra Nevada-Cascade and Rocky mountains. Perhaps the great ice sheet was instrumental in pushing americana eastward and separating it geographically from caurina." The present occurrence of americana in Alaska and British Columbia is thought to have been by invasion from the east in postglacial time.

Davis' theory seems basically correct but subject to correction in detail. The presence of caurina in the southern Rocky Mountains suggests that it is not a Pacific Coastal species in the common sense. Had americana occupied northern British Columbia in pre-Wisconsin Time, it and not caurina would be expected to occur in the southern Rocky Mountains today, for the form found in British Columbia almost certainly would have been forced into the Rockies. The range now occupied by caurina in the Rocky Mountains is so extensive as to suggest that martens could not have migrated into all of it from the Pacific Coast since Vashon Time, even had the region been unoccupied by any species of marten. The presence of americana in Alaska and British Columbia suggests that it arrived in those areas before caurina and that had the Rocky Mountains been unoccupied by martens in pre-Wisconsin time, americana and not caurina would have reached the Rockies first. It appears that caurina occupied much of western North America in pre-Wisconsin Time and was forced southward into the southern Rocky Mountains and along the Pacific Coast by Vashon-Wisconsin ice.

The separation of americana and caurina may be supposed to have occurred before the pre-Vashon-Wisconsin interglacial interval, perhaps by a glacier similar to but antedating the Vashon-Wisconsin glaciation.

The martens of western Washington (Martes caurina caurina) are a coastal race. Those of northeastern Washington belong to a race of the Rocky Mountain Fauna, and are referred to M. c. origenes. Davis (1939: 132) refers the martens of Idaho to Martes caurina caurina. I have compared specimens from Idaho with animals trapped for fur from the Pacific Coast proper and feel that the animals from northeastern Washington and those from Idaho are more like origenes than caurina, although perhaps not typical. The animals from the Pacific Coast proper are caurina and have darker heads and brown instead of yellow patches on the throat.

Martes pennanti.—Fishers are found throughout the Cascade Mountains and probably were widely distributed over western North America in pre-Wisconsin Time.

Mustela erminea.—The distribution of ermines along the coast of northern California and in the Cascade-Sierra Nevada of Oregon and California indicates, as does their differentiation there, that they ranged southward to these areas before and during Vashon-Wisconsin Time.

In immediate pre-Vashon-Wisconsin Time, the dark race streatori probably occurred in western Washington. The race murica probably occurred in the Blue Mountains then, as it does today, but probably occurred also in the Cascades of Washington. The descent of the Vashon glaciers probably displaced streatori from the northern part of its range, at least temporarily. In the Cascades, murica was likewise forced southward. Ermines related to the northern richardsonii were forced into northern Washington and Idaho by the Wisconsin ice. They probably were unable to live on the barren, unglaciated plains of eastern Washington but persisted in Idaho.

The ranges of the three forms at the maximum extent of the Vashon-Wisconsin may be reconstructed as follows: streatori in southwestern Washington; murica in the southern Cascades and the Blue Mountains; invicta stock in northern Idaho. While so isolated, the ermines of the southern Cascades probably mingled, to a certain extent, with streatori and developed the characters that now separate gulosa from both murica and streatori. The intermediate nature of gulosa has been mentioned by Hall (1945: 85).

The retreat of the ice allowed streatori to move north and invicta to move north and east into Washington and the northeastern Cascades. To a lesser extent, gulosa may have moved north. The poorly-marked race olympica probably evolved from streatori in the Recent. It is difficult to account for the dark race fallenda.

It must have evolved from streatori in the Recent but the origin of such a strongly marked race in such a short time is surprising. It might be mentioned that a similarly differentiated race of chipmunk, Eutamias amoenus felix, occupies much the same range.

Mustela frenata.—The long-tailed weasels of the Pacific Coast behave as a plastic group and clearly show the effect of the Vashon-Wisconsin Divergence. The range of the coastal race, altifrontalis, indicates that it was isolated in southwestern Washington during Vashon Time. In that period, or shortly after, it extended its range southward but only along the extreme, coastal area of Oregon (see Hall, 1936: 101). Following the retreat of the ice it extended its range northward to the deglaciated area of western Washington.

Also following the retreat of the ice, a Great Basin subspecies (nevadensis) extended its range northward. This race seems to have been more adaptable and successful than other kinds of Great Basin mammals, for it extended its range farther northward, eastward and westward than most.

A third race, washingtoni, was isolated in the southern Cascade Mountains during Vashon Time and became differentiated from both altifrontalis and nevadensis. It is now found in the Cascades from central Oregon north to Mount Rainier. It is difficult to see why it did not extend its range to include the northern Cascades when the glacial ice left, but it did not. Instead altifrontalis entered the northern Cascades from the west and nevadensis did the same from the east. Weasels obtained in habitats north of Mt. Rainier are intergrades between altifrontalis and nevadensis.

One is reminded here of the douglasii group of Thomomys talpoides in which subspecies did not move north of Mt. Rainier in postglacial time. The area north of Mt. Rainier was populated instead by gophers of the fuscus group, subspecies of which invaded the area from the east. Perhaps Mt. Rainier itself served as a barrier to alpine mammals in the immediate post-Pleistocene. Perhaps Mustela f. washingtoni will eventually extend its range northward, displacing the altifrontalis-nevadensis intergrades from the habitats to which washingtoni may be better adapted.

The Blue Mountains of southeastern Washington are occupied by a weasel (effera) that has a more extensive range in eastern Oregon. The range of this race has probably not changed materially for a long period of time.

One would expect the weasels from extreme northeastern Washington to be referable to the race oribasa, of the Rocky Mountain Fauna. Instead they are intermediate between that race and the Great Basin race, nevadensis. Apparently nevadensis was so dynamic and adaptable that it actually entered the geographic ranges of surrounding races for some distance. In view of Sumner's theory for the retention of subspecies, one might say that the population pressure of nevadensis on the periphery of its range is stronger than the opposing pressure of some surrounding races.

Mustela vison.—Pending a review of the minks of North America, little can be said concerning their historical distribution in the state of Washington. From the general range of the species in western North America, one would expect some effect of the Vashon-Wisconsin Divergence to be apparent. There is some evidence for this. Minks from Idaho and adjacent parts of British Columbia are distinctly less reddish than minks from the area about Puget Sound, as noted by Davis (1939: 138).

Gulo luscus.—The range of the subspecies luteus, peculiar to the Cascades and Sierra Nevada suggest that the wolverine may have been forced southward in the Cascades and there isolated during Vashon Time. The differences separating the southern race from the northern may have been developed while the two populations were isolated. The range of the wolverine was probably more extensive in glacial and immediate postglacial time than at present.

Lutra canadensis.—The otter of western Washington seems to be a member of the Pacific Coastal Fauna. Little can be said regarding the distributional history of the species in the state, for specimens from eastern Washington are not numerous enough to permit of a person certainly establishing their systematic position.

Spilogale gracilis.—The western race of the civet cat (latifrons) seems to be a coastal race, isolated in southwestern Washington and western Oregon during Vashon time. The eastern race, saxatilis, is a race of the Great Basin Fauna, that has entered the state from Oregon and that will probably extend its range to the north.

Mephitis mephitis.—Of the four subspecies of skunks occurring in Washington, two seem to have been resident in the state during Vashon Time. The western race, spissigrada, was probably isolated in southwestern Washington and extended its range northward, in the deglaciated area of western Washington, after the retreat of the ice. Another race (notata) was probably isolated in the southeastern Cascades and adjacent Oregon. M. m. hudsonica of the Rocky Mountain Fauna entered the northeastern part of Washington after the ice retreated from there. A race of the Great Basin Fauna, major, entered southeastern Washington from Oregon and may eventually extend its range farther north.

It is interesting to note that both of the western races, spissigrada and notata, both of which probably developed in Washington during Vashon Time, occupy limited ranges in adjacent Oregon (Bailey, 1936: 308).

Taxidea taxus.—This species has probably long been resident on the Columbian Plateau and in southeastern Washington. For the early distributional history of the species see Hall (1944: 17). Pleistocene remains, referable to this race, have been found in Franklin County.

Vulpes fulva.—The red fox of the Cascades was probably isolated there during Vashon Time by glacial ice. Its range extends southward in the Cascades to Oregon. The fox of eastern Washington is probably a member of the Rocky Mountain Fauna that lived in the Blue Mountains of southeastern Washington in Wisconsin Time and that emigrated to northeastern Washington in Recent Time.

Canis latrans.—The distributional history of the coyote in Washington is not clear.

Canis lupus.—The dark wolf (fuscus) of western Washington is probably a coastal race. The race that may have occurred in northeastern Washington probably was an invader from the Rocky Mountain Fauna, and the race that possibly occurred in southeastern Washington would be assumed to have long been a resident of the area.

Felis concolor.—The cougar of western Washington is a coastal race, probably developed while isolated in southwestern Washington and western Oregon. The cougar of northeastern Washington probably entered the state with other Rocky Mountain species, early in the Recent. The cougar of the Blue Mountains of southeastern Washington has probably long been resident there.

Lynx rufus.—The bobcat of western Washington seems to be a coastal race that was isolated in either southwestern Washington or western Oregon by Vashon ice. It has since extended its range into southern British Columbia. The bobcat of eastern Washington seems to be a member of the Great Basin Fauna that has spread to some forested areas on the periphery of the more arid life-zones.

Lynx canadensis.—The lynx is an element of a northern fauna that was probably forced southward into the Cascades and Rocky Mountains. Its range was probably more extensive, as is indicated by the scattered records of its occurrence in Oregon (Bailey, 1936:271).

Marmota monax.—The woodchuck invaded northeastern Washington in the early Recent with the Rocky Mountain Fauna.

Marmota flaviventris.—The yellow-bellied marmot is a typical member of the faunas of the Great Basin and the southern Rocky Mountains. It has doubtless entered southeastern Washington from eastern Oregon at an early time. In northeastern Washington, west of the Columbia River, it occupies alpine habitat, but it does not occur farther east, where Marmota monax is found, or in the Cascades where Marmota caligata lives.

The yellow-bellied marmots are great wanderers, and commonly are found in scattered outcrops far out on the Columbian Plateau. There is even one record for western Washington, near Bellingham, Whatcom County. This individual must have crossed some low pass in the Cascades from the area about Lake Chelan. There are records of eastern Washington birds occurring in this same area, so it seems likely that the marmot was a natural stray and not an animal that escaped from captivity.

Marmota caligata.—The absence of the hoary marmot from the Cascades of Oregon, and the presence there of Marmota flaviventris, indicates that the species did not occur in the southern Cascades of Washington during Vashon Time. Presumably the hoary marmot is a member of the fauna of the northern Rocky Mountains and entered the Cascades of Washington in the Recent, after which it spread widely and rapidly owing to lack of competition with any established species of marmot.

Marmota olympus.—This species has probably lived in the Olympic Mountains since pre-Vashon Time.

Citellus washingtoni.—This ground squirrel has probably lived on the Columbian Plateau since before Wisconsin Time.

Citellus townsendii.—The Townsend ground squirrel probably entered the Yakima Valley area from Oregon. The differences between it and its relatives in Oregon indicate a considerable period of isolation but one far shorter than the period during which washingtoni is presumed to have been isolated from townsendii.

Citellus columbianus.—The Columbian ground squirrel might have been forced southward in the Rocky Mountain area by the Wisconsin glaciation, might have lived in southeastern Washington since then, and might have invaded northeastern Washington in the Recent with other species of the Rocky Mountain Fauna.

Citellus beecheyi.—This ground squirrel is known to have entered Washington about 1915 from Oregon.

Citellus saturatus.—The mantled ground squirrel of the Cascades probably evolved, from the lateralis stock, as a separate species while isolated in the southern Cascades during Vashon Time. It is a poorly differentiated species and may actually be instead a strongly marked subspecies.

Citellus lateralis.—The golden-mantled ground squirrels of northeastern and southeastern Washington are closely similar. It is deduced that connectens of southeastern Washington developed the differences that characterize it while isolated, from the main stock, in the Blue Mountains area of Washington and Oregon.

The race found in extreme northeastern Washington (tescorum) probably reached that area in relatively recent times. Its range in Washington is more restricted than that of several other members of the Rocky Mountain Fauna; areas of suitable habitat west of the Columbia River are not inhabited by these ground squirrels. Its range in Washington is almost exactly that of (Marmota monax).

Tamias minimus.—The least chipmunk of the Yakima Valley is the same race (scrutator) as that occupying the Great Basin area of Oregon and Nevada. It must have crossed the Columbia in relatively recent times. Had it been resident in the isolated Yakima Valley area for any considerable period of time, the development of distinctive racial characters there would be expected. Perhaps, then, it has not been resident there as long as has the Townsend ground squirrel which, though closely related to the ground squirrel of eastern Oregon, is racially distinct.

The least chipmunk of the Columbian Plateau is thought to be racially distinct from its relatives in the Yakima Valley and eastern Oregon. Probably it reached the Plateau very early in the Recent. It has probably not been separated from the parent stock as long as has the ground squirrel (Citellus washingtoni) of the plateau. The ground squirrel is specifically rather than racially distinct.

Tamias amoenus.—The distributional picture of the yellow pine chipmunks in Washington is complex. (Fig. 81.) Certain habits of these mammals doubtless have modified what was probably the original postglacial distribution of the species. Chipmunks are diurnal and natural selective factors for color possibly operate more strongly on animals active by day than on nocturnal animals. Yellow pine chipmunks are neither forest nor desert inhabitants. Indeed, dense forests or open deserts serve as barriers to their distribution. They prefer brush lands, open woods, and other habitats where there is food and cover but abundant sunlight. In such habitats they are almost independent of altitude, temperature and humidity. They live in the Olympic Mountains where rainfall is heavy and humidity high. They live and breed at considerable altitudes in the Cascades, even in the crater of Mount Rainier, where snow, ice and freezing conditions exist the year around. On the other extreme, they occupy the low, open pine forests and brush lands at the lower edge of the Arid Transition Life-zone where temperatures, in summer, are high and rainfall scarce.

We find in the present distribution of the species in the Cascade-Sierra Nevada chain and the Rocky Mountains, indication that the species had a wide geographic range over western North America previous to the Vashon-Wisconsin glacial interval. Probably the range of the species extended in an arc, from the Rocky Mountains across northern Washington to the Cascades, around the basaltic plateau desert in eastern Washington and Oregon. Presumably the descent of the Vashon-Wisconsin glaciers broke this arc into two parallel geographic ranges, the Rocky Mountains and the Cascade-Sierra Nevada chain, with a desert area between.

Almost every species of forest-dwelling animal had its range separated into two parts by the southward movement of the glaciers. Most of these forest-dwelling species were composed of relatively homogeneous stocks, although the yellow pine chipmunk probably was not. The extensive range of tolerance of the yellow pine chipmunk to altitude and climate and its unique habitat requirements cause it to meet radically different natural selective factors. The predators of the chipmunks near Wenatchee, Chelan County, would include: rattlesnake, gopher snake, badger, striped skunk, prairie falcon, red-tailed hawk and other predominantly desert-dwelling species. The chipmunks at Stevens Pass, in the mountains to the west, would have to contend with: marten, black bear, goshawk, bald eagle and other alpine predators. At the present time, the chipmunk of the eastern Cascades is racially distinct from that of the higher Cascades. Geologic and botanical evidence indicates that the Columbian Plateau was a desert in pre-Wisconsin Time. We suppose that a transition from alpine conditions in the Cascades to desert conditions on the Columbian Plateau existed even in pre-Wisconsin Times. We suppose also that the chipmunk existed in this transition area and in the Cascades before Wisconsin Time and in the southern and southeastern Cascades during Wisconsin Time. We further suppose that the differences separating the transition area race (Tamias amoenus affinis) from the mountain race (T. a. ludibundus) came about through natural selection and not as a result of geographic isolation. The principal difference between the two is the paler color of the race in the transition area.

The descent of the Vashon-Wisconsin glaciers, then, found two races of the yellow pine chipmunk in the Cascades. Chipmunks living north of the Columbian Plateau, in northern Washington and British Columbia, were probably forced southward onto the inhospitable plains of the plateau and exterminated. Farther east, north of northeastern Washington, chipmunks from the north were probably forced southward to compete with resident chipmunks.

The range of Tamias amoenus luteiventris in Washington, Idaho and Montana is most unusual (See Howell, 1929; Davis, 1939). From a compact range in Montana, two long fingers reach northward and westward. The western finger crosses Idaho to end in the Blue Mountains of Oregon and Washington. The northern finger crosses northern Idaho, northeastern Washington and extends on into southern British Columbia. Between these two fingers of the range of luteiventris another race (canicaudus) is found. This race occupies a more lowland area than does luteiventris. The range of luteiventris in the northern Rocky Mountains is extensive. Presumably this race occupied an area farther north in pre-Wisconsin Time and was forced southward to its present range by the Wisconsin glaciers. The original population occupying extreme eastern Washington and adjacent Idaho was Tamias amoenus canicaudus. The pre-Wisconsin range of this race might have been more extensive. At any rate, luteiventris which was driven southward displaced canicaudus, or some other race of chipmunk, from much of the Rocky Mountains south of the glacier. The northern chipmunks were adapted to more boreal conditions and perhaps otherwise better suited to environmental conditions of the northern Rocky Mountains. A small population of the older established race (canicaudus) persisted in lowland areas of eastern Washington and adjacent Idaho.

Regarding the range of canicaudus, surrounded by the range of luteiventris on three sides and faced by desert on the west, Davis (1939: 220) writes, "It may be that, of these two races, luteiventris has a greater range of tolerance to environmental conditions and, thus, is able to succeed in areas to which canicaudus is not adapted. This inference is supported by the fact that luteiventris occupies a large range which is diversified geographically and climatically, whereas canicaudus seems to be limited to a much smaller, more nearly uniform area." Seemingly canicaudus now exists only in an area ideally suited to it, and one where it can successfully compete with the generally more adaptable and successful luteiventris. The maximum extent of the glacial ice, then, found luteiventris the dominant chipmunk in the northern Rocky Mountains, with an isolated population of canicaudus in eastern Washington and adjacent Idaho.

The topography of the ground moraine exposed by the retreat of the Vashon-Wisconsin glaciers was a barrier to many species of mammals. The rough, rocky surface with thin soil probably first supported mosses and grasses, then brush, and later trees. The earlier stages of plant succession on the deglaciated ground probably presented ideal habitat for yellow pine chipmunks. Certainly the races immediately adjacent to the glaciers extended their ranges farther north than many species. In eastern Washington, T. a. luteiventris spread to the northeastern corner of the state and on into British Columbia. In the northern Cascades, T. a. affinis spread northward and eastward, across the Okanogan River, into northeastern Washington as far as the range of luteiventris. The chipmunk of the higher Cascades (ludibundus) likewise extended its range northward into British Columbia. In the northwestern Cascades of northern Washington and southern British Columbia, a richly-colored race, T. a. felix, now occupies a limited geographic range. This race doubtless originated from ludibundus stock but the method of its development is unknown. Perhaps in early postglacial time, selective factors developed in chipmunks of the western slopes of the Cascade Mountains the rich, dark color of felix. The ancestral ludibundus may have given rise to a pale race, affinis, in the arid eastern Cascades and a dark race, felix, on the humid western slope of the Cascades. This seems improbable for there is no trend to darker color on the western border of the range of ludibundus south of the range of felix, and instead, affinis may have given rise to ludibundus. A more appealing hypothesis is that a local mutation in some ludibundus stock so changed the range of tolerance of a portion of the population that it was allowed to enter the more dense habitat along the coast north of the Fraser River and, there, isolated by habitat selection, it developed the characters of felix. Population pressure later forced it eastward until the eastern border of its range again met the range of the ancestral race, ludibundus.

The chipmunks of the Olympic Mountains probably reached their present range from the Cascades. Their probable path of emigration was westward from Mt. Rainier, along the glacial outwash train of Nisqualli Glacier, to the moraine and outwash apron of the Vashon Glacier and thence to the Olympics. So similar are the chipmunks of Mt. Rainier and the Olympic Mountains that Howell (1929) included Mt. Rainier in the range of caurinus.

Briefly summarized, the probable pre-Vashon-Wisconsin distribution of chipmunks of the species Tamias amoenus in Washington was: ludibundus in the higher Cascades; affinis in the eastern Cascades; canicaudus in eastern Washington and adjacent Idaho; and luteiventris in the area north of the range of canicaudus. The descent of the Vashon-Wisconsin ice restricted but did not materially alter the ranges of ludibundus or affinis. On the east, luteiventris was forced southward to compete with canicaudus and displaced it over a large region, especially in mountainous areas. Following the retreat of the ice, luteiventris, affinis, and ludibundus extended their ranges northward over the deglaciated territory. A stock of ludibundus that moved westward from Mt. Rainier became isolated and gave rise to caurinus. In some less obvious development, ludibundus stock gave rise to felix north of the Fraser River in the Cascades.

Tamias ruficaudus.—Until a better understanding of the range of this chipmunk and its relation to other Tamias is gained, uncertainty will remain concerning its distribution in the past.

Tamias townsendii.—This is a typical coastal species that ranges southward, along the coast, to California. The lowland race of western Oregon and Washington (townsendii) probably occurred no farther north than southwestern Washington when the Vashon Glacier was in place. Chipmunks of this species in the Cascades and in the southern Olympic Mountains probably developed independently the slightly paler color that separates cooperi from townsendii. The tendency for species of the Pacific Coastal Fauna of the Cascades and the Olympic Mountains to be paler than their lowland relatives is widespread.

After the retreat of the ice, both races probably moved northward. Perhaps because of its alpine adaptations, cooperi has moved farther than townsendii. Also, townsendii, in the lowlands, ranges to the Fraser River, a barrier not encountered by cooperi.

Sciurus griseus.—This species of the Pacific Coastal Fauna probably entered Washington from Oregon since the retreat of the Vashon Glacier. It has probably entered the state in relatively recent times.

Tamiasciurus hudsonicus.—The two species of red squirrels, T. hudsonicus and T. douglasii, are specifically distinct and probably became differentiated in the Pleistocene when southward moving glaciers cut in two the range of the ancestral stock. The morphological differences are too great, comparatively, to have occurred during the Vashon-Wisconsin Divergence. T. hudsonicus probably occupied a range in pre-Wisconsin Time that included the Rocky Mountains and areas to the north. Glacial ice probably restricted the range of hudsonicus in Wisconsin Time but after the retreat of the ice hudsonicus moved northward to reoccupy its former range. It also moved westward across northern Washington to the Cascades, where it met the range of douglasii. Farther north, it moved westward to the Pacific, thus occupying an area that, in pre-Vashon time, probably was occupied by douglasii.

Tamiasciurus douglasii.—The Douglas squirrel probably occupied the coastal region of Oregon, Washington and British Columbia in pre-Vashon Time. The descent of the ice restricted its range to southwestern Washington and areas to the south. After the retreat of the ice it moved northward somewhat but, like other coastal species, the movement was slow. Meanwhile hudsonicus from the Rocky Mountain Fauna, had spread to the coast of British Columbia.

Glaucomys sabrinus.—This flying squirrel is a plastic species. It inhabits all of the forested parts of Washington. The distributional picture presented by the 5 races (Fig. 92) which occur in Washington is complicated. The ranges of 3 of these lie principally outside the state of Washington.

The race oregonensis occupies Washington and Oregon west of the Cascades; fuliginosus occupies the Cascades of Washington, Oregon and southern British Columbia; columbiensis occupies the interior valleys of British Columbia and adjoining Washington; latipes occupies the northern Rocky Mountains of British Columbia, northern Idaho and extreme northeastern Washington; and bangsi occupies the Blue Mountains of Washington and Oregon and a wide range in Idaho and eastward.

The differences separating the race oregonensis from other subspecies found in Washington are relatively great. This lowland race is smaller and richer in color. The other races exhibit slight but relatively constant differences. The relatively great difference between oregonensis and the other races indicates that oregonensis was isolated from the remainder of the species for a considerable time. Presumably oregonensis was a strongly differentiated coastal race in pre-Vashon Time and occupied most of western Washington and Oregon. The descent of the Vashon ice restricted the range of oregonensis to southwestern Washington and western Oregon. The descent of the ice forced a northern race, fuliginosus, southward into the range of oregonensis. The northern race, adapted to boreal conditions, was able to compete successfully with the established oregonensis only in mountainous areas. In the Cascade Mountains, fuliginosus extended its range southward to southern Oregon.

The descent of the Wisconsin ice in eastern Washington forced the flying squirrels of adjacent British Columbia southward into the Rocky Mountains. These squirrels were probably closely related to fuliginosus, or to bangsi, which latter race already may have been established farther south in the Rocky Mountains. The Blue Mountains of southeastern Washington were probably inhabited by bangsi in Wisconsin times, or even earlier. The retreat of the Vashon-Wisconsin glaciers allowed the flying squirrels to extend their ranges northward. In western Washington oregonensis moved to southern British Columbia. In the Cascade Mountains the more boreal fuliginosus moved much farther northward and, north of the Okanogan Valley, spread eastward to the arid, interior valleys of British Columbia. Subsequent differentiation in the population of the arid, interior valleys developed the slightly differentiated race columbiensis. Farther east, flying squirrels from the northern Rocky Mountains moved northward. Northeastern Washington and adjacent British Columbia were occupied by latipes, derived from bangsi.

Thomomys talpoides.—Views as to the probable historical distribution of this plastic group have been presented in an earlier report (Dalquest and Scheffer, 1944: 308-333). This may be briefly summarized as follows.

Previous to Vashon-Wisconsin Times, pocket gophers occupied at least the Cascade Mountains and the Columbian Plateau of Washington. The race occupying the Columbian Plateau, devexus, was probably racially distinct in pre-Wisconsin time. The descent of the Vashon-Wisconsin glaciers isolated gophers in the southern Cascades. Three racial stocks developed there: shawi in the Mount Rainier area; limosus in the Columbia River Valley south of the Cascades; and immunis in the mountainous area between the other two races. At the maximum extent of the Wisconsin ice, gophers from the Columbia River Valley (limosus) were able to cross the Simcoe Bridge and reach the Blue Mountains. With the retreat of the Wisconsin ice, the Simcoe Bridge was closed. Gophers isolated in the Blue Mountains developed the racial characters of acqualidens and those between the Blue Mountains and the Columbia River intergraded with the desert race, devexus. These intergrades, which have, also, some characters of their own, bear the name columbianus. Gophers in the southern Cascades (limosus) moved westward on prairie-like river terraces to Clark County where, isolated, they became racially distinct (douglasii).

Gophers from the Mount Rainier area (shawi) moved westward on glacial outwash trains to the extensive outwash aprons of the Vashon glaciers in the area about Puget Sound. Here they multiplied and spread to the Olympic Mountains. Growth of forest on the original outwash apron broke the area into numerous isolated prairies. Gophers in the Olympic Mountains (melanops) were isolated from those in the area about Puget Sound. Six distinct races originated on the isolated prairie (glacialis, tacomensis, pugetensis, yelmensis, tumuli, couchi).

Following the retreat of the glacial ice from eastern Washington, pocket gophers from the Blue Mountains of Oregon (wallowa) moved northward into Washington and gophers from the Rocky Mountain Fauna of Idaho moved onto the deglaciated part of northeastern Washington. From northeastern Washington they spread westward to the Cascades and thence southward to meet the native gophers of the Cascades in the Yakima Valley Area. No racial differentiation in these gophers occurred; all are referable to fuscus. Where fuscus and the native gophers came together in the Yakima Valley, a new race, yakimensis, developed.

Perognathus parvus.—Three races of the pocket mouse occur in Washington. Two of these (lordi and columbianus) occur on the Columbian Plateau. Like many desert species that occur on the Columbian Plateau, the pocket mice are rather different than their relatives in eastern Oregon. Presumably they have been isolated on the plateau since before Vashon-Wisconsin Times.

The range of the pocket mouse of southeastern Washington, Perognathus parvus parvus, is continuous with the range of the race in Oregon. This same race occurs in the Yakima Valley, whence it probably arrived from Oregon in relatively recent time.

The distribution of pocket mice on the Columbian Plateau, in eastern Oregon and in the Yakima Valley resembles that of the least chipmunk in those areas. It is also similar to, but of more recent origin than, that of the ground squirrels, Citellus washingtoni, and townsendii.

Dipodomys ordii.—This kangaroo rat enters the desert area of southeastern Washington from Oregon. It may be expected eventually to cross the Columbia River to the Yakima Valley and the Snake River to the Columbian Plateau.

Castor canadensis.—Two races of beavers occur in Washington. One, found in southwestern Washington and northwestern Oregon, is dark with a short, wide skull. The other, ranging over most of the state, is paler with a longer, narrower skull.

The form now found in southwestern Washington and adjacent Oregon (idoneus) was probably isolated there by the Vashon glaciation and developed its characters while isolated. The other race, leucodonta, was probably widely spread in Wisconsin Time. Beavers are present in Moses Lake, in almost the center of the Columbian Plateau. Beavers might well have lived in the streams of melt water that emerged from the Wisconsin Glacier. The beavers of western Washington, save those in the extreme southwest, are like the beavers of eastern Washington. It seems likely that the race leucodonta originated north of the state of Washington and was forced southward by the Vashon-Wisconsin glaciers. This northern race, adapted to boreal conditions, competed with the resident coastal race, idoneus, and occupied much of its range. The distribution of the races of muskrat in Washington closely resembles that of the beavers.

Onychomys leucogaster.—The desert-dwelling grasshopper mouse has doubtless entered eastern Washington and the Yakima Valley from eastern Oregon at a relatively recent time.

Reithrodontomys megalotis.—The harvest mouse, like the grasshopper mouse, seems to have entered Washington from Oregon at a relatively recent date. Within the last ten years it has extended its range into the Okanogan Valley in British Columbia.

Peromyscus maniculatus.—Six subspecies of Peromyscus maniculatus occur in the state of Washington. The geographic range of one of these (rubidus) lies mainly in the states of California and Oregon and includes, so far as is known, a single small island in the Columbia River that is politically within the state of Washington. Another (hollisteri) is restricted to certain islands in northern Puget Sound and obviously has become subspecifically differentiated in postglacial time. The remaining four subspecies, namely oreas, austerus, artemisiae and gambelii, have extensive geographic ranges. These subspecies are not confined to their geographic ranges by geographic barriers. Deer mice occur in the deep forests and the open desert, on high mountains and in low valleys, and are almost everywhere the commonest species of mammal present.

The study of several populations of deer mice from any general area usually shows small but constant differences between them. Dice (1939: 21) studied stocks of deer mice from nine localities in southeastern Washington and found significant differences between several of them. A statistical study of mice from the San Juan islands shows that the population of almost every island is different in one or more respects from the mice of any other island. Geographically separated populations of "wild caught" mice of the subspecies austerus, of the mainland, were statistically compared and significant differences were found between these populations, too. Small, differentiated populations are to be found in many parts of the state, and each subspecies appears to be an assemblage of such tiny genetic units.

These genetic units probably are the microgeographic races of Debzhansky (1937). They have been intensively studied by Sumner (1917 A, B) and Dice. An especially important paper by the latter author (1940) summarizes much of the available information on speciation in Peromyscus and clearly discusses the microgeographic races of Peromyscus.

The numerous microgeographic races of Peromyscus maniculatus in Washington present diverse combinations of characters which could result from the random fixation and elimination of genes (Wright. 1932: 360-362). Such a hypothesis, however, requires at least partial isolation of the populations involved. The mechanism of such isolation, in such populations of deer mice as we have studied, is not readily apparent. Some microgeographic races are not separated by noticeable geographic or ecologic barriers and the distance between their ranges is not too great to be traversed by a deer mouse. The tendency to remain on a home range may have the same effect as isolation would be supposed to have.

The work of Murie and Murie (1931: 200-209, 1932: 79) is enlightening in this respect. These authors found that mice residing in a locality tended to remain in that locality; individuals trapped and marked were retaken in the same locality a year later. Individuals released some distance from the point of capture remained where released or returned to the point of capture. Transported individuals did not spread at random. The home instinct was developed in young as well as in old mice. Two mice in the gray pelage, four to eight weeks old, returned to their home ranges from distances one and two miles away. The authors fix the home range of an individual Peromyscus m. artemisiae in Teton County, Wyoming, at approximately one hundred yards in diameter.

This home-range instinct is essentially a lack of incentive for individual mice to emigrate to new localities where mice of the same species are already established. This may partly account for the microgeographic races of deer mice in Washington.

Dice (1939: 21) pointed out that, except in color, the differences in nine stocks of mice from southeastern Washington could not be correlated with environmental factors. We have found this to be true of microgeographic races throughout the state of Washington.

Of the four subspecies of deer mice that occupy extensive geographic ranges in Washington, one, oreas, is a long-tailed form that seems not to intergrade with austerus, a neighbor in western Washington that has a tail of moderate length. These two and gambelii, a short-tailed form with which oreas intergrades, are easily distinguished. In eastern Washington two short-tailed subspecies, gambelii and artemisiae, are currently recognized. The taxonomic relationships of these two subspecies are complex. The subspecies gambelii has an extensive geographic range in Oregon and California. These mice, with short tails, occur in the Wallula Water Gap of southeastern Washington and on the Columbian Plateau. To the west the desert conditions of the Columbian Plateau fade into the Transition Life-zone forests of the eastern Cascade Mountains. The pale, short-tailed desert mice (gambelii) gradually change to the dark, long-tailed subspecies, oreas, that occupies the Cascade Mountains.

North of the Columbian Plateau, in northeastern Washington, the deer mice are darker and relatively longer-tailed than on the Columbian Plateau. Some populations are distinctly reddish, almost as reddish as oreas. Although assigned to artemisiae, they are almost identical with populations of deer mice from the eastern Cascade Mountains, known to be intergrades between oreas and gambelii. This fact, and the presence of surprisingly oreas-like characters in some microgeographic races in extreme northeastern Washington, may indicate that the race called artemisiae is a group of intergrades between gambelii and an oreas-like mouse that has become extinct.

Intergradation between gambelii and artemisiae is normal and takes place gradually where the ranges of the two subspecies meet. The same is true of intergradation between oreas and gambelii in the eastern Cascade Mountains. West of the Cascade Mountains the range of oreas meets the range of austerus. These two subspecies appear not to interbreed in nature, since no intergrades were taken at any of the numerous localities in western Washington where the mice were trapped. Pure populations of the two subspecies exist within a few miles of each other. In the valley of the Skykomish River, in the western Cascades Mountains, from the town of Skykomish, King County, to the lowlands to the west, only austerus was found. In the coniferous forests of the mountains above Skykomish, only oreas was taken. Several pairs, each an oreas and an austerus of the other sex, were kept from four to six months, and one pair was kept for a year, but they did not reproduce. The oreas were from the upper Skykomish Valley and the austerus were from Seattle, King County. Along the border of the ranges of the two subspecies in the Skykomish River Valley, a definite habitat preference was noted. The coniferous forests were occupied by oreas and brush or deciduous forests by austerus. Within the range of austerus and within the range of oreas only one subspecies is found whether the habitat be coniferous forest or thickets of alder and willow, but where the ranges of the two subspecies meet austerus occurs only in the thickets of aspen and willow and oreas occurs only in the coniferous forest.

The morphological characters that separate oreas from austerus, namely, larger size, richer color, and longer tail, are all features that might be associated with a more arboreal existence in dark, coniferous forests. Our observations show that oreas is, to a large extent, arboreal. Traps nailed to tree trunks six to eight feet from the ground and set for flying squirrels often caught oreas in the Skykomish River Valley. On one occasion I walked up a leaning tree trunk to set a trap, fifty feet from the ground on the trunk of another tree that was upright. An oreas was found in this trap the next morning. Svihla (1933: 13) relates how a specimen of oreas that escaped from a live trap took refuge in a tree when pursued. We have set numerous traps for flying squirrels in the area about Puget Sound. As far as memory and field notes serve, we have never taken austerus in these traps. Our observations on the habits of austerus are much more abundant than those on oreas, but for austerus no evidence of arboreal activities has been obtained.

There are, then, two subspecies that do not interbreed, each capable of existing in any ecologic niche that will support deer mice. Where the ranges of the two subspecies come together, they compete. The large size, richer color, longer tail, and perhaps arboreal habits of oreas give it an advantage in coniferous forests. The small size and dark color of austerus give it an advantage in other habitats, especially, perhaps, in winter, when the deciduous trees have shed their leaves.

The differences separating austerus from oreas would be expected to have developed under complete isolation. That oreas developed from austerus or austerus from oreas seems impossible. A glance at the distribution map (Fig. 107) shows that the range of austerus clearly separates the range of oreas into two segments. The range of austerus tapers out to the north, east and west. On the south austerus intergrades with rubidus from Oregon, a subspecies from which it is but slightly differentiated.

The geographic behavior of the four subspecies of deer mice that occupy extensive areas in Washington may be summarized as follows: P. m. gambelii occupies southeastern Washington and intergrades normally with oreas in the eastern Cascade Mountains and with artemisiae at the northern edge of the Columbian Plateau; artemisiae, occupying northeastern Washington, closely resembles populations of mice that are known to be intergrades between oreas and gambelii and itself intergrades with both oreas and gambelii; oreas occupies most of western Washington, intergrades with its neighbors artemisiae and gambelii to the east, but does not intergrade with austerus, its morphologically more similar neighbor in the west; austerus occupies a range in western Washington that is almost surrounded by the range of oreas, a subspecies with which it apparently does not interbreed.

The relations of these four subspecies appear to be the result of certain great changes in the range of deer mice in the Pacific Northwest that occurred during and since the last Pleistocene glaciation. We reconstruct these changes as follows. In the Puyallup interglacial cycle, just previous to the last (Vashon-Wisconsin) continental glaciation, clines, or gradual transitions existed in the ranges of the deer mice along the Pacific Coast. The small, dark, short-tailed mice of the coastal redwood forests of California and Oregon became gradually larger, redder and longer-tailed to the north, climaxing in a large, red, long-tailed form in the spruce forests of southern Alaska and northern British Columbia. A similar cline existed inland. Small, pale, short-tailed mice of the Great Basin became increasingly larger, darker, and longer-tailed to the north, reaching a maximum in the spruce forests of northern British Columbia.

The development and advance of the Vashon-Wisconsin ice sheet exterminated mice over much of British Columbia and the northern United States. Long-tailed northern mice were forced southward and contacted the southern, short-tailed forms. The preglacial clines were thus destroyed.

What might be the southern part of the western cline may be noted in the deer mice of western Oregon today. From the southern coast of Oregon the mice (P. m. rubidus) do become larger, redder and longer-tailed to the north. The climax of this cline is now reached in austerus, of the Puget Sound area of Washington. The cline is not continued farther northward because the range of oreas is encountered.

The advance of the Vashon-Wisconsin ice from the north probably forced species of mammals southward, ahead of it, including the long-tailed northern deer mice which generation by generation encountered progressively shorter-tailed forms of resident mice. Perhaps the unfamiliar, and certainly the extremely frigid, conditions in the fore of the glacier exterminated the short-tailed individuals but favored the long-tailed mice, since the latter originally were adapted to a boreal environment. The climax of the ice advance found the glaciers just within the political limits of the United States and found the long-tailed mice spread before the ice front.

In western Washington the Vashon glacier advanced as far south as the southern edge of the Puget Sound area. Long-tailed northern mice advancing before it reached the Columbia River. This glacially swollen stream served as a natural barrier and prevented their southward extension. At this time the northern mice had traversed more than half the length of the original western cline. The northern mice, originating in a boreal habitat a thousand miles away, were unable to interbreed with the southern mice and such individuals as might have crossed the Columbia River never became established in Oregon. During the existence of the glacier in western Washington, the long-tailed northern emigrants competed with the resident deer mice of western Washington to the total elimination of the resident mice. The retreat of the Vashon Glacier from Washington found the northern mice in complete control of that part of the state from the Pacific Ocean to the Cascade Mountains.

In eastern Washington the Wisconsin Glacier advanced south to the northern edge of the Columbian Plateau. Northern mice advancing before it probably did not survive on the treeless plateau but existed in forested areas of northern Idaho and driftless areas of northern Washington. No natural barriers separated the northern mice from the pale, short-tailed forms. The nonuniform topography perhaps allowed more mingling of the two types where climatic conditions permitted. Intergradation in some places as well as competition and elimination of one form or another in other places occurred. Following the withdrawal of the Vashon ice and the establishment of soil and forests on the deglaciated land, the long-tailed mice of western Washington (P. m. oreas) apparently spread northward, unhindered by competition, until they reached southern Alaska. The deep coniferous forests of western Washington presented conditions acceptable to oreas and it persisted there despite postglacial changes in climate.

Postglacial changes in climate did, however, permit the dark, short-tailed mice (rubidus) to cross the Columbia River and to become established in suitable habitats, namely the deciduous jungles of the river valleys. From these points the mice spread northward through the lowlands of western Washington, infiltrating the range of oreas, competing with it, and driving it from the lowlands. This movement is in progress today. By logging and clearing of lands for agriculture man has considerably speeded the invasion of the southern mice. Slight differentiation of the short-tailed mice north of the Columbia River (austerus) separates them from their parent race, rubidus.

In the dense forests along the Pacific Coast of Washington, austerus did not become established. This area includes most of the land west of Puget Sound. There is a narrow band of austerus that extends along the eastern and part of the northern edge of the Olympic Peninsula, where they have probably invaded in relatively recent time.

On the Oregon side of the Columbia River the range of rubidus is continuous from the Pacific to the Cascades. On the Washington side of the river, oreas extends from the Pacific to eastern Wahkiakum County, where the range of austerus starts. At the border of the ranges of the two subspecies, ecological conditions determine the ranges; oreas occurs in the Douglas fir and hemlock forests and austerus occurs in the jungles of alder and salmonberry in the stream valleys. The range of austerus extends from eastern Wahkiakum County east along the Columbia, to western Klickitat County. In a north-south strip across the Columbia, through the ranges of rubidus in Oregon and austerus in Washington, normal intergradation is apparent. By gradual degrees rubidus changes to austerus. In a north-south strip farther west, through the ranges of rubidus and oreas, the same transition of the Oregon rubidus is seen, namely an approach toward austerus. The cline is, of course, abruptly terminated by the range of the dissimilar oreas.

On Puget Island, a small island lying in the Columbia River in western Wahkiakum County and politically within the state of Washington (see Scheffer, 1942) a population of deer mice occurs that resembles rubidus more closely than austerus. This island lies in the river between the ranges of rubidus and oreas. The lack of intergradation between these two subspecies has probably kept the Puget Island population pure rubidus. Puget Island is a junglelike lowland locally known as "tideland."

The San Juan Islands of northern Puget Sound were thoroughly glaciated in Wisconsin Time and probably were under thousands of feet of ice when the Vashon Glacier was at its maximum extent. The subspecies of deer mouse occurring there now is hollisteri, a race similar to oreas in color, body size and cranial characters and probably derived from oreas. P. m. hollisteri differs from both oreas and austerus in its much shorter tail. Shortness of tail is apparently a product of insularity in northwest coastal mice. The transition from long-tailed mainland mice to short-tailed island mice is shown by Hall (1938A: 461). When oreas first occupied the area about Puget Sound (this area is occupied by austerus today) some individuals probably reached the San Juan Islands soon thereafter. Contact between oreas and hollisteri is now prevented by the presence of austerus between their ranges. Of course, a water barrier separates austerus from hollisteri but austerus does occur in pure form on some islands in Puget Sound (not on any of the San Juan Islands), for instance, on Whidby Island. One wonders why austerus has not established itself on some of the San Juan Islands but considering the degree of difference between hollisteri and austerus, I doubt that the two would interbreed if they did occur together.

On Vancouver Island, British Columbia, a short-tailed, austerus-type of mouse occurs in the lowlands and a long-tailed, oreas-type of mouse in the mountains. Vancouver Island is a large island (16,400 square miles). Apparently a stock of austerus from the mainland reached Vancouver Island and were able to find suitable habitat and compete with and drive out the established oreas in the manner that they probably did in the western Washington lowlands. The large Vancouver Island offers far more variety of habitat and opportunity for establishment of emigrating mice than do the smaller San Juan Islands, the largest of which is Orcas (57 square miles).

Following the withdrawal of the Wisconsin ice from eastern Washington, numerous minor movements and adjustments of deer mice seem to have taken place. Long-tailed, oreas-type of mice were exterminated on the Columbian Plateau if, indeed, they ever became established there. Long-tailed mice did apparently become established in driftless areas and forested areas to the south of the drift border. With the establishment of soil and forests on the deglaciated land, the short-tailed gambelii and the long-tailed mice became thoroughly intermixed. In some areas, especially near the type locality of artemisiae, the gambelii characters of the mixture predominate at the present time. Deer mice from the Okanogan Valley differ from gambelii only in slightly larger size and darker color. In other areas, notably near Metaline, Pend Oreille County, the oreas characters of the mixture dominate at the present time. Mice from here are large and red and differ from typical oreas in having relatively short tails. Other less marked segregations of characters are numerous, in Idaho and British Columbia as well as in Washington. Cowan (1937) has described Peromyscus m. alpinus, isolated in a mountainous area of British Columbia. This seems to be a form derived from oreas-type stock.

With the reëstablishment of soil and forests on the deglaciated land of British Columbia north of Washington, a northward extension of the gambelii-oreas mixture occurred. Another invasion was taking place at this time, however. Peromyscus m. arcticus spread onto the deglaciated land from the north or east, ahead of artemisiae (the gambelii-oreas mixture). This new invader intergraded with artemisiae as well as with oreas. Further collecting and studies are required in this area before the relationships of the three subspecies can be completely understood.

If geographic ranges are assigned to the named subspecies of deer mice that occur in Washington, it must, in part, be done arbitrarily. The deer mice of the San Juan Islands are all referred to the subspecies hollisteri. Only Puget Island, Wahkiakum County, is considered to be inhabitated by rubidus. The boundary between the ranges of austerus and oreas is sharply defined and further collecting by resident naturalists should result in detailed mapping of the boundary.

The ranges and distribution of the deer mice of eastern Washington are less clearly defined than those of western Washington. Peromyscus m. gambelii exists in its purest state on the Columbian Plateau. Here the Columbia River makes a convenient boundary to the west. Pure Peromyscus m. oreas exist in the Cascade Mountains. In the area between the Columbian Plateau and the Cascades the deer mice are variously intermediate between gambelii and oreas and, over most of the area, are nearest to gambelii. This might be considered a natural area of intergradation such as commonly occurs between the ranges of subspecies. These intergrades, however, are similar to Peromyscus m. artemisiae and the area occupied by these intermediates is connected on the north with the range of artemisiae. Thus Osgood (1909: 61) regards specimens from Easton and Wawawai, in the area of intergradation, as artemisiae or intergrades between gambelii and artemisiae. Taylor and Shaw (1929: 22) include the entire area of intergradation in the range of artemisiae. This treatment, although convenient to the student of geographic variation, is apt to conceal the evolutionary and historical influences. These influences may be appreciated better if the intergrades from each locality are referred to the subspecies they most closely resemble.

The specimens upon which the name artemisiae was based came from a narrow tongue of zonally lower country that extends northward from the range of the lighter-colored gambelii. As might be expected, topotypes are lighter in color than specimens from the north, west and east. Nevertheless, the type locality is within a geographic area that is occupied principally by a darker race, artemisiae, to the north of gambelii. The topotypes of artemisiae may be considered to be intermediate between gambelii and the darker, northern race. Thus the name artemisiae becomes available for the mice of the general area in question. The mice of the area immediately to the east of the type locality, in Washington and presumably in British Columbia and Idaho also, are essentially a mixture of the subspecies gambelii and a now mostly extinct and unnamed race that probably resembled oreas. Local variations of populations from within this area are extreme but some segregation of color and length of tail has taken place. Mice from mountainous areas resemble oreas while mice from the lowlands resemble gambelii, or, more exactly, mice from coniferous forests resemble oreas while mice from other areas resemble gambelii.

South of the area of racial mixture in northeastern Washington, in the Blue Mountains of southeastern Washington, the deer mice are like gambelii except in slightly darker color. Mice from the Blue Mountains are darker and browner than gambelii, not more reddish. There is no indication of adulteration with oreas stock. Since the Blue Mountains are a forested area and are far south of the drift border, we suppose that deer mice existed there through the last glacial period and that their dark color is an adaptation to forest habitat.

Mice similar to those of the Blue Mountains have an extensive range in Idaho (Davis 1939: 290). These mice have relatively uniform racial characters and constitute a "good" subspecies.

At present the deer mice of northern Washington, southeastern British Columbia, northern Idaho, northeastern Oregon, western Montana and northwestern Wyoming are called artemisiae. The mice of this extensive area are, however, of two genetic types: that type with mixed racial characters that lives in northeastern Washington and probably also farther east along the Wisconsin drift border, and that type that occurs farther south in Idaho and seems to constitute a stable subspecies.

The separation of these two types may be desirable. Detailed study of the deer mice from the area now assigned to the range of artemisiae may show that the name subarcticus (Peromyscus texanus subarcticus Allen, 1899) is applicable to the southern form. The type with mixed racial characters must be called artemisiae. If the two types are eventually separated, the mice from the Blue Mountains of Washington will be referable to the southern form.

Neotoma cinerea.—The wood rat found over most of Washington. Neotoma c. occidentalis, probably entered the state from eastern Oregon early in the Recent and spread over most of the state. The wood rat of the Blue Mountains (alticola) probably developed from occidentalis.

A coastal race of the wood rat (fusca) occurs in western Oregon. This race, if it occurred in western Washington in pre-Vashon Time, was eliminated in Vashon Time or subsequently. In Oregon it lives in deep forests (Bailey, 1936: 174). In Washington occidentalis occupies but a small part of the ecologic niche occupied by fusca in Oregon. Elimination of fusca from Washington through competition with occidentalis seems highly improbable. Should fusca ever cross the Columbia River and become established it would probably spread to a considerable part of western Washington.

Synaptomys borealis.—The lemming mouse seems now to be retreating northward and was an arctic species forced southward by the Vashon-Wisconsin glaciers. Unlike other alpine species, it seems to be unable to exist for long in isolated mountain areas.

Phenacomys intermedius.—The heather vole, like the lemming mouse, probably was forced southward by the Vashon-Wisconsin glaciers. In the Cascade and Rocky mountains it found suitable habitat and spread southward to almost the lower end of the Sierra Nevada in California. The Cascade race moved eastward on the Puget Bridge to the Olympic Mountains after the retreat of the Vashon ice, and northward in the Cascades. Northeastern Washington was reinvaded by the subspecies of the Rocky Mountain Fauna.

Clethrionomys gapperi and CALIFORNICUS.—The two species of red-backed mouse found in Washington were probably distinct in pre-Vashon Times. At the maximum extent of the Vashon ice, californicus was probably found in western Oregon and gapperi in the Blue Mountains, where idahoensis was developed, and in the southern Cascades (cascadensis). During or shortly after Vashon Time, gapperi crossed the Puget Bridge to become established in the Olympic Mountains. After the retreat of the ice, gapperi moved northward and eastward from the Cascades and californicus crossed to western Washington from Oregon and displaced gapperi from the lowlands.

Hinton (1926: 215) separated the American Clethrionomys into three groups, suggesting that Old World counterparts of each group exist. Davis (1939: 308) gives an excellent analysis of the emigrational history of the American species, and points out the close relationship of the Siberian and Arctic-American forms. He suggests that the rutilus group invaded Arctic-America from Siberia at the close of the last glaciation.

Two other groups are recognized by Davis, who assumes that both arose from a common ancestral stock and divided into two stems, one of which (gapperi group) followed the main Rocky Mountain course southward and worked eastward across Canada while the other (californicus group) followed down the Pacific Coast. Davis states, "This southward extension of range in America probably took place in the Pleistocene, but almost certainly the present southern range of the genus in the West was not reached until late in, or after, that period."

Our studies of the Clethrionomys of Washington indicate the essential correctness of Davis' conclusions. The separation of the two groups, however, probably was caused by southward moving glaciers and the separation of the mice into two stocks closely paralleled the divergence of other groups, such as that of the snowshoe rabbits. The two groups of red-backed mice are more sharply separated than was thought by Davis. The intermediate color of the back of C. g. idahoensis, mentioned by Davis, seems to be merely coincidental. The essential difference in the two groups is the sharply marked red band of the gapperi group as opposed to the general red area on the dorsal surface of the californicus group. Clethrionomys gapperi nivarius has been considered a derivative of occidentalis because the range of the latter surrounds the Olympic Mountains, where nivarius is found. Considering the immediate post-Pleistocene movements of mammals from the Cascades to the Olympic Mountains, so clearly illustrated in Thomomys, Tamias amoenus, and Phenacomys, a means is indicated by which Clethrionomys of the gapperi group might have reached the Olympics. The apparent lack of intergradation between occidentalis and nivarius gives proof of their relatively distant relationship. C. nivarius seems not to have been derived from occidentalis, and apparently does not belong to the californicus group. It belongs instead to the gapperi group, and I consider it to be a subspecies of gapperi. In no sense is it intermediate between the two groups. The other form considered by Davis to be intermediate between the two groups is caurinus. This mouse has not yet been taken in Washington, although it may eventually be found on Point Roberts, on the Fraser River delta. Its distribution is paralleled by that of many other mammals that are definitely not of the Pacific Coastal Fauna.

The californicus group, I feel, contains only the races of Clethrionomys californicus, while the gapperi group contains C. gapperi and its races, including caurinus, and possible other species.

Possibly intergradation occurs between C. californicus occidentalis and C. gapperi. Nevertheless, I fail to find evidence of such intergradation. I have taken C. gapperi nivarius and C. californicus occidentalis within ten miles of each other, but each retained its distinctive characters with no evidence of intergradation. In the case of C. gapperi saturatus and C. californicus occidentalis the proof is less conclusive. In spite of numerous attempts to trap Clethrionomys in the area geographically intermediate between their ranges, I have taken none. Though common along the coast, occidentalis becomes progressively scarcer to the east, being rare in the vicinity of Seattle and apparently absent from the western base of the Cascades. So far as is known, the ranges of caurinus and occidentalis are separated by the Fraser River.

Microtus pennsylvanicus and MONTANUS.—The Pennsylvania meadow mouse is closely related to Microtus montanus. Certain races of montanus, notably those from southern Oregon, California, and northern Nevada, closely resemble pennsylvanicus externally and cranially. From the central part of its range northward, montanus becomes progressively less like pennsylvanicus. The races nanus and canicaudus are quite different from pennsylvanicus both externally and cranially, and in addition the anterior loop of the second molar is less constricted; often it is not constricted at all. Microtus pennsylvanicus and Microtus montanus occur together over parts of the northern Rocky Mountains. Where the two species came together, pennsylvanicus occurs with races of montanus that are most unlike it.

Microtus pennsylvanicus kincaidi closely resembles races of Microtus montanus that occur in southern Oregon, California, and Nevada. It is larger, darker, and longer-furred than Microtus pennsylvanicus funebris from Washington. Seemingly pennsylvanicus and montanus diverged previous to Vashon-Wisconsin Time. The stock that gave rise to montanus spread over the Great Basin while pennsylvanicus ranged farther east. Some of the montanus stock worked northward in the Rocky Mountains. Microtus pennsylvanicus had meanwhile moved westward to the Rocky Mountains. The two stocks met and behaved as full species.

Microtus pennsylvanicus probably occupied northeastern Washington in the interglacial cycle preceding the Recent. The advance of the Wisconsin ice eliminated most of these mice. The glacier dammed the Columbia River and caused it to turn southward from its basalt-marginal course and take a path over the Columbian Plateau. Along this glacial river a population of Microtus persisted to become kincaidi.

While the Wisconsin ice was at its maximum extent, Microtus montanus from the Blue Mountains crossed the Simcoe Bridge to the Yakima Valley and the eastern Cascade Mountains. The closing of the Simcoe Bridge isolated these mice, which subsequently became slightly differentiated, as canescens. Another stock moved westward along the Columbia River to western Oregon. This stock is now called Microtus canicaudus but is probably racially rather than specifically distinct from Microtus montanus nanus.

With the retreat of the Wisconsin ice, montanus extended its range northward from the Yakima Valley along the eastern Cascade Mountains to extreme southern British Columbia. Microtus pennsylvanicus funebris entered northeastern Washington with other elements of the Rocky Mountain Fauna.

At present, pennsylvanicus occurs in northeastern Washington while montanus is found in southeastern Washington and the eastern Cascade Mountains. The Okanogan River Valley separates their ranges. Eventually montanus may extend its range to northeastern Washington and pennsylvanicus to the Cascades, the two forms occurring together as they do in Montana, Idaho and Colorado. The isolation of kincaidi on the Columbian Plateau seems complete and the probability of its range reaching that of its related species seems slight.

Microtus longicaudus.—The later distributional history of the long-tailed meadow mouse is not yet clear.

Microtus townsendii.—This Pacific Coastal species probably lived west of the Sierra Nevada-Cascade Mountains since the early Pleistocene. It has extended its range northward since the retreat of the Vashon ice and has reached some of the islands in Puget Sound and the Strait of Georgia. This species seems to be related to Microtus richardsoni but the two species probably separated at an early time.

Microtus richardsoni.—The water rat of the Cascade Mountains seems to be have been forced southward into Washington and Oregon by the descent of the Vashon-Wisconsin glaciers where it became isolated from the water rat of the northern Rocky Mountains. After the retreat of the ice, both forms have moved northward. Bailey (1900) records macropus from Bonner County, Idaho, not far from northeastern Washington but in Washington up to this time, macropus has been recorded only from the Blue Mountains of the southeastern part of the state.

Microtus oregoni.—The later historical distribution of the creeping mouse was probably the same as that of townsendii.

Lagurus curtatus.—The distribution of this species of the Great Basin Fauna has probably changed little if any since the late Pleistocene.

Ondatra zibethicus.—The distribution of the two races of muskrat that occur in Washington is almost exactly that of the beavers. Probably one form was isolated in southwestern Washington and northwestern Oregon during Vashon Time and another, more adaptable, race occurred in eastern Washington. After the retreat of the ice the adaptable race spread widely but the muskrats of the lower Columbia River changed their range little or not at all.

Aplodontia rufa.—The race of Aplodontia found in the Cascades of Washington was probably confined to the southern Cascades in Vashon Time and has since spread northward to reoccupy the range as far north as southern British Columbia.

The presence of a mountain beaver in western Washington that is indistinguishable from the race rufa, found in the Cascades of Oregon, is most surprising. In Oregon, pacifica occurs in the western lowlands and rufa in the mountains to the east. In Washington rufa occurs in the western lowlands and rainieri in the mountains to the east.

The offset in range of rufa seems best explained by assuming that all of western Washington was once occupied by mountain beavers (rufa) that spread from the Cascades of Oregon to the Cascades of Washington and thence to the western Washington lowlands. This must have occurred early in the interglacial cycle preceding the Vashon Glaciation. While confined to the southern Cascades, rainieri developed the larger size that now separates it from the ancestral rufa that occurs to the west and south of it.

Zapus princeps.—The coastal race of the jumping mouse was probably distinct from the more inland population before Vashon-Wisconsin Times. The differences between them were probably accentuated while the Vashon-Wisconsin glaciers separated their ranges. The western race (trinotatus) was isolated in the southern Cascades and southwestern Washington. After the retreat of the glaciers, trinotatus moved northward through western Washington and the Cascades into British Columbia. The race kootenayensis of the adjacent Rocky Mountains moved eastward through northeastern Washington to the Cascades. The race oregonus, found in the Blue Mountains, has probably been resident there since it evolved from the populations to the east.

Erethizon dorsatum.—I have inadequate basis for speculation concerning the historical distribution of the porcupine.

Ochotona princeps.—The descent of the Wisconsin ice separated the western pikas into two populations. One was confined to the Cascade-Sierra Nevada system and another to the Rocky Mountains. Two races are now found in the Cascades of Washington. One, brunnescens, inhabits the higher Cascades and another, fenisex, the eastern edge of the Cascades. The range of brunnescens extends southward into Oregon while the range of fenisex extends farther north in British Columbia than does that of brunnescens. The principal difference between the two races is the smaller size and paler color of fenisex. In Washington, fenisex occupies a slightly more arid habitat than brunnescens. Further, fenisex lives in talus principally of basaltic rock while brunnescens lives in talus of granitic rock. The basaltic talus is more finely fractured, offering smaller crevices in which pikas can conceal themselves. The granitic rock, on the other hand, forms talus composed of fragments of large size. Freshly fractured granite is pale, whitish gray. After weathering, however, it becomes blackish as the more soluble, pale feldspars are removed, leaving the black hornblend and biotite exposed. Freshly fractured Columbian basalt is blackish but, after weathering, becomes rusty, reddish brown.

In Washington the two races maintain their distinctiveness because selective factors in the basalt talus of the eastern Cascades favor the smaller size and paler color of fenisex while in the higher Cascades, selective factors in the granitic batholith favor larger size and darker color.

The present range of brunnescens in Oregon indicates that this race was the pre-Wisconsin resident of the Cascades of at least southern Washington. Probably fenisex evolved in the arid interior of British Columbia. In color fenisex is intermediate between the dark brunnescens and the pale cuppes of the western spurs of the Rocky Mountains. Probably fenisex was forced southward into the eastern Cascades by the Wisconsin ice and inhabited the area east of the range of brunnescens. This eastern area was not occupied by brunnescens because the basaltic talus was of small size. After the retreat of the ice, fenisex (adapted to more arid habitat than brunnescens), spread northward to the relatively dry valleys of the interior of British Columbia.

The distinctness of brunnescens and fenisex is maintained by selective factors of the habitats they occupy but the zone of intergradation between the two is broad. A tendency towards paleness is noticeable in specimens from as far west as the eastern side of Mount Rainier.

The pikas in the Rocky Mountain area have given rise to a number of races. The pale, small race of northern Idaho, cuppes, entered northeastern Washington with other members of the Great Basin Fauna after the retreat of the ice.

Lepus townsendii.—The white-tailed jack rabbit has probably lived on the Columbian Plateau ever since or even before the time when the Wisconsin ice bordered the plateau on the north.

Lepus americanus.—Snowshoe rabbits were probably spread over forested parts of Washington in pre-Wisconsin time. A coastal race, washingtonii, was probably distinct from the remainder of the species at an early time. It, and its kindred races klamathensis and tahoensis, are very different from races derived later from the Rocky Mountain Fauna. From this it is deduced that washingtonii was a member of the Pacific Coastal Fauna before the advance of the last continental glaciers.

The snowshoe rabbits now found in the Cascade Mountains of Washington are racially distinct from populations occurring to the north and east, but are more closely related to the northern and eastern rabbits than they are to washingtonii. This race, cascadensis, probably lived in the area north of the state of Washington in pre-Wisconsin interglacial time. The snowshoe rabbit of northeastern Washington was probably a race having an extensive range in the Rocky Mountains from which pineus in the Blue Mountains developed. The descent of the Vashon-Wisconsin glaciers found washingtonii restricted to western Oregon. It might have persisted also in southwestern Washington but, had this been the case, we would expect a broader zone of intergradation between washingtonii and cascadensis than actually exists.

The glaciers forced cascadensis southward into the Cascades of southern Washington. The difference between washingtonii and cascadensis and the narrow zone of intergradation between them, indicate that the two races were not in contact in pre-Vashon Time. The presence in the Cascades of Oregon of a race related to washingtonii rather than cascadensis also supports this view. The snowshoe rabbits of northeastern Washington were probably eliminated from areas where the ice was in place. The effect of the glaciers in nearby areas was probably less on snowshoe rabbits than upon other species.

Following the retreat of the glaciers, washingtonii reinvaded western Washington and spread northward through the lowlands to the Fraser River. In the Cascades, cascadensis moved even farther north. L. a. pineus of the Rocky Mountain Fauna invaded northeastern Washington from adjacent areas to the south. Another race, columbiensis, spread from the interior valleys of British Columbia to the western part of northeastern Washington in probably relatively recent times. The post-Wisconsin history of the distribution of this race is uncertain.

Lepus californicus.—The black-tailed jack rabbit occurs throughout the sagebrush areas of eastern Washington, except in the Okanogan Valley. It invaded Washington from the south recently (Couch, 1927: 313). The first blacktails were thought to have entered Walla Walla County about 1870. Here they were checked by the Snake River. About 1905 they crossed the Snake River, on ice, and by 1920 had spread over much of the Columbian Plateau. In January, 1920, they crossed the Columbia River in two places, on ice jams, and by 1927 had spread north and west over the sagebrush areas between the Columbia River and the Cascade Mountains. When Couch, in 1927, published his account, he predicted that the blacktail would eventually spread to the Okanogan Valley. This has not yet occurred although it is still to be expected.

It should be noted that the migrational history of the black-tailed jack rabbit is known only because the animal is large, spectacular, and diurnal, and therefore noticed by resident ranchers, and because the facts came to the notice of a competent biologist. Migration of a less conspicuous mammal, for example, a mouse, would rarely be detected.

Sylvilagus nuttallii.—The cottontail might have been resident on the Columbian Plateau during Wisconsin Time but probably it invaded, or perhaps reinvaded, the Plateau from eastern Oregon in the Recent.

Sylvilagus idahoensis.—Too little is known about this rabbit in Washington to hazard a guess as to its recent distributional history.

Cervus canadensis.—The elk emigrated from Siberia to North America in the late Pleistocene but previous, certainly, to Vashon-Wisconsin time. Probably the coastal race was distinct from the interior population in the preceding interglacial cycle. The descent of the last continental glaciers, in Washington, separated the elk of the Pacific Coastal Fauna from the Rocky Mountain Fauna. After the retreat of the ice the coastal race moved northward to southern British Columbia and the Rocky Mountain race moved northward and westward through British Columbia. Northeastern Washington was reoccupied by the Rocky Mountain elk.

Remains of elk have been found associated with human artifacts on the northern part of the Columbian Plateau. The plateau is poorly suited to elk but a few may have persisted there until late historic time. The remains may have been brought by Indians from northeastern Washington. The remains included teeth and portions of the skull and it seems unlikely that these would have been carried any great distance.

Odocoileus hemionus.—The American deer probably evolved in North America. In this respect they are unlike the elk, moose and caribou, all of which emigrated from Asia to America in the Pleistocene. Odocoileus hemionus and virginianus probably diverged from a common stock in the Pliocene.

The black-tailed deer was probably a member of the Pacific Coastal Fauna at an early time and distinct from the mule deer before the last interglacial cycle. Probably the mule deer lived in the eastern Cascades and on part of the Columbian Plateau in Wisconsin Time. They occur on the plateau in limited numbers at present and their remains have been found associated with human artifacts in the Grand Coulee area.

Odocoileus virginianus.—The white-tailed deer ranges from the Atlantic to the Pacific and from Canada to Mexico. The species was probably abundant in the Pacific Northwest in the Pleistocene, perhaps in Vashon-Wisconsin time, but has since largely given way to the black-tailed and mule deer. The race O. v. leucurus now occupies an extremely small range. The accounts of early naturalists indicate that it was more abundant and had a wider range 100 years ago. Probably leucurus was once an important member of the Pacific Coastal Fauna.

The inland race, ochrourus, is a typical member of the Rocky Mountain Fauna. It and leucurus were probably derived from a common ancestor in the late Pleistocene.

Alce americanus.—The moose occurs in Washington as a casual wanderer from the Rocky Mountain Fauna to the east.

Rangifer montanus.—The caribou occurs in northeastern Washington as a winter migrant from the north. It was probably of more regular and extensive occurrence in the past.

Antilocapra americana.—The antelope probably was a casual wanderer to southeastern Washington and perhaps to the Columbian Plateau from eastern Oregon before white man reached Washington.

Bison bison.—The buffalo, like the antelope, probably occurred in southeastern Washington and on the Columbian Plateau only as a casual wanderer from Oregon in postglacial time.

Ovis canadensis.—Mountain sheep reached North America from Asia in the Pleistocene. By Vashon-Wisconsin Time they had spread southward, perhaps to Mexico. The descent of the Vashon-Wisconsin ice in Washington presumably separated the canadensis and californiana type of sheep, the former being confined to the Rocky Mountain Fauna and the latter to the Cascade-Sierra Nevada chain and adjacent parts of the Great Basin.

Mountain sheep probably persisted in the southern Cascades of Washington and on the Columbian Plateau during Vashon-Wisconsin times. After the retreat of the ice, these sheep (californiana) moved northward slightly, both in the Cascades and on the Columbian Plateau. Remains of sheep are to be found with human artifacts in the Grand Coulee area today. When white man first reached the state, sheep existed throughout the Cascades and on part of the Columbian Plateau. Only a pitiful remnant remains in the extreme northern Cascades.