Cascade Mountains where, for most of Wisconsin time, they were isolated
in the southern Cascades. Examples are _Sorex palustris_, _Martes
caurina_, _Martes pennanti_, _Gulo luscus_, _Vulpes fulva_, _Lynx
canadensis_, _Tamias amoenus_, _Thomomys talpoides_ (_douglasii_ group),
_Phenacomys intermedius_, _Microtus richardsoni_ and _Ochotona
princeps_. In each of these species little or no subspecific variation
has occurred between the populations in the Cascades of Washington and
the Cascades of Oregon.
While the ice sheet existed in Washington there may have been relatively
little movement of the mammalian fauna. There is definite evidence of a
brief contact between the Rocky Mountain Fauna of the Blue Mountains and
the fauna of the southern Cascades. For example, the pocket gopher of
southeastern Washington (_Thomomys talpoides aequalidens_) is most
closely related to the gopher of the Simcoe Anticline, and the
long-tailed meadow mouse (_Microtus longicaudus halli_) of the Blue
Mountains closely resembles the meadow mouse of the Yakima Valley.
Mammals of the Blue Mountains and those of the southern Cascades may
have come into contact on the Simcoe-Horseheaven Hills Anticline, which
now stretches 150 miles from the Cascades to the Wallula Water Gap.
Excepting the easternmost 40 miles, it is timbered. East of the
Columbia, a continuation of the anticline and other hills reaches to the
Blue Mountains. Supposedly, in Wisconsin Time, this anticline possessed
a more humid climate and the habitat was essentially the same as that of
an alpine meadow today. The forms on the two ends of the anticline that
are closely related inhabit humid, meadow habitat. In an earlier paper,
Dalquest and Scheffer (1944: 316) named this connection the Simcoe
Bridge. Its existence was so strongly indicated by the distribution of
pocket gophers in Washington that we supposed that the study of many
other species would show that they crossed this bridge. However, study
of additional species shows that for them the Simcoe Bridge was of only
slight importance; there appears to have been but little mingling of the
fauna of the Blue Mountains and the Cascades by way of the bridge. The
Columbia River probably acted as an effective barrier to many forms that
might otherwise have utilized it. The forms that did cross on this
bridge are species known to be active in winter and to emigrate over
considerable areas through tunnels under the snow (Davis, 1939: 257).
The pocket gopher and long-tailed meadow mouse may have crossed the
Columbia, under a cover of snow, when the river was frozen over. The
Columbia has frozen over at the Wallula Water Gap in historic times.
[Illustration: FIG. 19. Pend Oreille River (or Clark Fork of the
Columbia) from a point near Newport, Washington, looking south,
June 13, 1938. (Fish and Wildlife Service photo by Victor B.
Scheffer, No. 67.)]
Great movements of mammal species came after the retreat of the
Vashon-Wisconsin ice. The greatest of these was the spread of the Rocky
Mountain Fauna northward and eastward to the Pacific. In this process,
northeastern Washington was inhabited by animals that probably came from
Idaho and Montana. Some of the species from farther north, as for
example the caribou, may first have been forced into Idaho and Montana
by the glaciers. The invasion of northeastern Washington probably was
not a mass movement of an entire fauna, because invasion seems to be
still going on. As yet the woodchuck and striped ground squirrel of the
Pend Oreille Mountains have not crossed the Columbia River, a
relatively minor barrier in northeastern Washington. The mountains west
of the Columbia are occupied instead by the yellow-bellied marmot, a
member of the Great Basin Fauna, and there is no ecologic counterpart in
these mountains of the golden-mantled ground squirrel.
Also the invasion of the Cascade Mountains by a number of Rocky Mountain
species may have been an intermittant or gradual movement. The red
squirrel and Rocky Mountain subspecies of jumping mouse now are present
in the extreme northeastern Cascades, where they possibly arrived
relatively recently. The squirrel is competing with the coastal species
already present and may eventually supplant it. The same may be true of
the two forms of jumping mouse.
The invasion by the Rocky Mountain Fauna was rapid as compared with that
of the Pacific Coastal Fauna. Evidence of this was presented in an
earlier paper (Dalquest and Scheffer, 1944: 310), where it was shown
that the gophers of the _douglasii_ group, isolated during the Vashon
time in the southern Cascades, made only a few feeble postglacial
movements and then only when conditions were ideal. In this same time
the _fuscus_ group of gophers moved from Idaho and virtually surrounded
the range of the _douglasii_ group. This tendency to immobility seems to
have been characteristic of every member of the Pacific Coastal Fauna.
If the retreat of the Vashon and Wisconsin glaciers occurred at the same
time, both faunas had an equal opportunity to invade the deglaciated
area. Yet, the Pacific Coastal Fauna actually moved northward along the
coast only to the Fraser River area, and slightly farther in the
Cascades.
Possibly the two glaciers retreated at different times. The Wisconsin
Glacier was a piedmont glacier, fed by valley glaciers to the west and
east, and may have disappeared when the feeder glaciers dried up. The
Vashon Glacier was instead an ice cap, supposedly self-supporting much
in the same manner as is the Greenland Ice Cap, and may have persisted
longer than the Wisconsin glacier. If it did persist longer it formed a
barrier to the northward emigration of coastal species of mammals.
Possibly, also, the whole of the Pacific Coastal Fauna possessed an
inherent sluggishness resulting from their long residence in the uniform
climate and habitat of the Pacific Coast. Certainly the species show
today great habitat specialization as compared with species of the Rocky
Mountain Fauna. Also, there are fewer individual mammals per unit of
area in western Washington than in northeastern Washington. The
persistence of the Vashon Glacier, an inherent lack of incentive to
emigrate, or retention of a favorable environment, may account for the
relatively small area invaded by the Pacific Coastal Fauna.
The Olympic Mountains, on the Olympic Peninsula, rise above the
timber-line and are surrounded by forested lowlands which in a sense
isolates this mountain range. Early workers, notably Elliot, obtained
specimens of mammals from the Olympics and described numerous races,
principally, it appears, on the supposition that because the range was
somewhat isolated it should possess a unique fauna. Subsequent revisions
of groups of mammals have indicated that most of the names proposed, on
the basis of specimens from the Olympics, were either invalid or
pertained to mammals found also in the Cascades.
The mammals of the Olympic Peninsula appear to be divisible into three
groups. A majority of them fall within the first group, namely coastal
races possessing wide ranges in the lowlands of western Washington. The
second group consists of species of the Rocky Mountain Fauna but with
close relatives in the Cascades. The third group includes but two forms,
both unique and found only on the Olympic Peninsula.
The first group includes nonalpine forms of the lowlands surrounding the
Olympic Mountains. For the most part these are identical with races of
the Puget Sound area. A few are slightly differentiated from the mammals
of the Puget Sound area but are the same as mammals from southwestern
Washington. As will be shown later, some differentiation in the Pacific
Coastal Fauna has occurred. This is thought to be evolution _in situ_,
rather than the result of mass movements. Many nonalpine Coastal mammals
occur in alpine habitat in the Olympics.
The second group consists of species of the Rocky Mountain Fauna. Their
relationship to the mammals of the Cascades is indicated in the two
parallel columns below.
OLYMPICS CASCADES
_Sorex palustris navigator_ _Sorex palustris navigator_
_Martes caurina caurina_ _Martes caurina caurina_
_Martes pennanti_ _Martes pennanti_
_Tamias amoenus caurinus_ _Tamias amoenus ludibundus_
_Phenacomys intermedius oramontis_ _Phenacomys intermedius oramontis_
_Clethrionomys gapperi nivarius_ _Clethrionomys gapperi saturatus_
Only two of these are racially distinct from their relatives in the
Cascades. Of these the chipmunk is a plastic species and breaks down
into many races in Washington. The chipmunks of the Olympics and of Mt.
Rainier are so similar that Howell (1929: 77) considered them as
identical and mapped Mount Rainier as an isolated part of the range of
the Olympic form (see account of _T. a. caurinus_). The relationship of
the red-backed mice, also, is close, but has been obscured by the usual
assumption of relationship between _californicus_ (_occidentalis_) and
_gapperi_. The principal difference between the alpine forms is the
pallor of _nivarius_. This pallor of mammals in general from the Olympic
Mountains is noteworthy, but in the red-backed mouse is exceptionally
noticeable. This pallor is discussed beyond in the paragraphs dealing
with differentiation. Mention should be made here of _Myotis keenii_.
This is a species which seems to have extended its range to Washington
from the north. The power of flight, of course, removes it from
consideration in attempting to reconstruct routes followed by
terrestrial mammals.
The route of the pocket gopher (_Thomomys_) in emigrating from the
Cascades to the Olympics (Dalquest and Scheffer, 1944: 310), was over
the outwash train of the Mount Rainier Glaciers, especially the
Nisqualli Glacier, to the extensive outwash aprons of the Vashon Glacier
around southern Puget Sound, and thence into the Olympic Mountains.
Under the conditions in early postglacial time this invasion route,
hereinafter termed the Puget Bridge, around the Pleistocene Lake Russell
(present Puget Sound), is thought to have been mainly an alpine meadow.
Indeed, the isolated prairies remaining today are the unforested
remnants of the outwash aprons (see Dalquest and Scheffer, 1942: 69) and
possess several species of alpine plants, notably the shooting star,
camas, and bear grass.
If the Vashon Glacier remained in place considerably longer than the
Wisconsin Glacier, these Rocky Mountain species may have invaded the
Cascades from northeastern Washington and travelled around the southern
edge of the Puget Glacier or of Lake Russell. The close relationship of
the races involved, however, suggests that the emigration took place
much more recently. The barriers to such movement even today are slight,
consisting principally of narrow areas of forest. For the water shrew,
an almost continuous water habitat still exists, by way of the Nisqualli
River, streams in the Puget Sound area, and the Satsop River in the
Olympics. Tree-living forms such as the fisher and marten might easily
travel the intervening distance today, and, by going along the forests
north of the Chehalis River, reach the Olympics without crossing more
than small streams and virtually without descending to the ground.
Chipmunks and mice probably utilized the prairie or meadow area of the
Puget Bridge, as did the gophers.
Considering the long existence of the Puget Bridge, it is surprising
that such forms as the pika, water rat and golden-mantled ground
squirrel did not cross to the Olympics. These forms are, however,
species of the higher or eastern slopes of the Cascades.
The third group of Olympic mammals includes the white-bellied water
shrew and the Olympic marmot, both indigenous forms.
The Bendire water shrew, _Sorex bendirii albiventer_, is not restricted
to alpine habitat but occurs throughout the Olympic Peninsula. Its
nearest relative is _S. b. bendirii_ of the rest of western Washington.
_S. b. albiventer_ differs from _bendirii_ only in possessing a
partially white ventral surface. We can only conclude that the white
belly of _albiventer_ is a mutation that the local environment has
favored and that the characters have, therefore, spread through the
population on the Olympic Peninsula. Occasional specimens are taken with
dark bellies characteristic of _bendirii_ (Jackson, 1928: 199).
The Olympic marmot, _Marmota olympus_, specifically distinct, and
apparently the only preglacial relic species of alpine mammal in the
Olympics, is most nearly related to _Marmota vancouverensis_ of the
unglaciated mountains of Vancouver Island, British Columbia. Both
_olympus_ and _vancouverensis_ are close relatives of _Marmota caligata_
which ranges southward into the Cascades of Washington.
The Columbia River in its course westward through the Cascade Mountains,
might be expected to act as a highway for the movement of mammals, but
the extent to which it has done so seems to be slight, at least in
postglacial time. The pocket gopher of southwestern Washington reached
the area about Vancouver from the southern Cascades by way of meadows on
the gravel terraces of Wisconsin glacial drift. No other mammal seems to
have extended this far. Several Great Basin species, such as the
cottontail, extend westward in the valley of the Columbia to the
vicinity of Bingen.
The mammals of western Oregon and southwestern Washington are closely
similar as are the plants and climate, despite the fact that the broad
Columbia River courses through the area and did so all through Recent
and Pleistocene times. Many species would be expected to have crossed
this barrier by swimming and rafting, and that they did so is indicated
by the large number of mammals which are identical or very closely
related on the two sides of the river.
Mammals which seem not to differ on the two sides of the river include:
_Scapanus townsendii_ _Citellus beecheyi_
_Scapanus orarius_ _Tamias townsendii_
_Sorex trowbridgii_ _Sciurus griseus_
_Sorex vagrans_ _Glaucomys sabrinus_
_Canis lupus_ _Castor canadensis_
_Felis concolor_ _Microtus townsendii_
_Lynx rufus_ _Microtus oregoni_
_Mephitis mephitis_ _Ondatra zibethicus_
_Spilogale gracilis_ _Zapus princeps_
_Procyon lotor_ _Odocoileus hemionus_
_Ursus americanus_
The following mammals are subspecifically distinct in western Washington
and western Oregon:
WASHINGTON OREGON
_Sorex bendirii bendirii_ _Sorex bendirii palmeri_
_Sorex obscurus setosus_ _Sorex obscurus bairdi_
_Neotoma cinerea occidentalis_ _Neotoma cinerea fusca_
_Peromyscus maniculatus austerus_ _Peromyscus maniculatus rubidus_
_Clethrionomys californicus _Clethrionomys californicus
occidentalis_ californicus_
_Microtus longicaudus macrurus_ _Microtus longicaudus abditus_
_Aplodontia rufa rufa_ _Aplodontia rufa pacifica_
The following species are found in western Oregon but do not occur in
western Washington:
_Vulpes fulva_ _Phenacomys albipes_
_Urocyon cinereoargenteus_ _Microtus canicaudus_
_Neotoma fuscipes_ _Thomomys bulbivorus_
_Phenacomys silvicola_ _Lepus californicus_
_Phenacomys longicaudus_ _Sylvilagus bachmani_
Several of these mammals which occur south of the river but not north of
it are common on the south bank, a few miles from favorable but
uninhabited territory on the north.
Seemingly the pre-Vashon faunas of western Oregon and Washington were
similar. Some species became extinct in Washington in the course of
Vashon isolation. Others persisted. The very close relationship of the
mammals of the first group indicates some crossing of the river. The
best known of such crossings was that of the Beechey ground squirrel
which, previous to 1915, was unknown in Washington. In 1915, when there
was no man-made bridge at White Salmon, it crossed the river and since
has spread over an area of at least 50 square miles. The distribution of
the mountain beavers is unusual in that the form in the lowlands of
Washington is indistinguishable from the subspecies in the Cascades of
Oregon.
The mammals that are racially distinct on the two sides of the
Columbia River merit careful scrutiny. The _Peromyscus_ of the two
sides more closely resemble one another than those of southern Oregon
resemble those of northern Oregon or than those of southern Washington
resemble those of northern Washington. For _Peromyscus maniculatus_,
the Columbia River is simply a convenient boundary for the separation
of two slightly different races. The Oregon race of the bushy-tailed
wood rat is a coastal type but the Washington form is the same as that
of eastern Washington. Seemingly the more eastern race spread to an
unoccupied habitat in western Washington. Other races that differ on
the two sides of the Columbia probably developed while separated by the
river.
[Illustration: FIG. 20. Rocky bluff along north bank of the Columbia
River near Lyle. Washington. March 20. 1939. Habitat of Beechey ground
squirrel and yellow-bellied marmot. (Fish and Wildlife Service photo
by Victor B. Scheffer. No. 640.)]
The San Juan Islands now possess a limited mammalian fauna.
Unfortunately the activities of man have somewhat changed the native
populations, especially by the introduction of the domestic rabbit
which is now a serious pest in the islands. The Douglas squirrel,
present on Blakeley Island, is said to have been introduced and one
resident claims to have first brought it to the island. Two different
persons claim credit for introducing the Townsend chipmunk on Orcas
Island but do not account for its presence on Lopez Island. The three
mammals most abundant and widely distributed in the islands are _Sorex
vagrans_, _Peromyscus maniculatus_ and _Microtus townsendii_. These
species, at least, probably reached the islands at an early time. The
two last named are now subspecifically distinct from their mainland
relatives. Other mammals which probably were established before the
arrival of the white man include the mink, otter, beaver, muskrat,
raccoon and black-tailed deer.
The Great Basin Fauna of eastern Washington exists as three units, one
on the Columbian Plateau, another in southeastern Washington and the
third in the Yakima Valley area. The desert species of the Yakima Valley
are more closely related to the species of eastern Oregon than they are
to those of the Columbian Plateau. In a number of respects the Columbian
Plateau gives indications of age. The ground squirrel, _Citellus
washingtoni_, is related to, but specifically distinct from _Citellus
townsendii_ of the Yakima Valley and eastern Oregon. _Perognathus parvus
lordi_ is a well-marked race, as is _Microtus pennsylvanicus kincaidi_
and _Thomomys talpoides devexus_. We suppose that these species were
present on the Columbian Plateau at least through the Recent and
probably through all of Wisconsin Time. The loess deposits of eastern
Washington seem to have been laid down in Wisconsin and Recent times.
These indicate an arid climate which, although probably cool, was
probably not so cold as to exterminate these species. On the other hand,
some species that are now abundant on the Columbian Plateau seem to have
arrived there relatively recently. The black-tailed jack rabbit, for
example, was unknown in eastern Washington before 1870 when it appeared
in Walla Walla County. In 1905 it crossed the Snake River on ice and
invaded the Columbian Plateau where it rapidly spread over the whole
area. In January, 1920, it crossed the Columbia in two places and spread
over the Yakima Valley.
The known facts of this movement were sufficiently impressive to cause
the author to study rather closely the distribution of mammals in this
area. The collection of bones from a cave along the Columbia River near
Vantage, Grant County, on the Columbian Plateau, is especially helpful
in this respect. This cave was first visited in 1938. It had been the
habitat of owls, bats, and primitive man. The floor of the cave was
buried under from one to three feet of bat guano, much of which had
been hauled away for fertilizer. Here and there we found traces of fire
and occasional piles of mussel shells. Some arrowheads and one beautiful
obsidian spear head were found, all buried in guano and about midway
between the floor and the top of the deposit. Remains of mammals were
abundant through the bat guano, and apparently had been brought to the
cave both by man and owls. The jaw of a mountain sheep was found. This
species was known to be present when the first settlers reached the area
(Cowan, 1940: 558). The remains of smaller mammals included gopher,
pocket mouse, muskrat, meadow mouse, deer mouse, coyote and white-tailed
jack rabbit. No remains of cottontail, black-tailed jack rabbit or
harvest mouse were found. The absence of the cottontail was especially
surprising, in that fully thirty skulls of white-tailed jack rabbits
were noted. The grasshopper mouse (_Onychomys_) was also absent, but
this species is not common. The two rabbits and the harvest mouse,
however, are abundant in the area today. The cottontail and harvest
mouse have only recently been recorded from the Okanogan Valley of
British Columbia (Cowan and Hatter, 1940: 9). The black-tailed jack
rabbit has never been taken there.
Apparently then, some species have only recently entered the Upper
Sonoran Life-zone of eastern Washington. They have, of course, reached
the state from Oregon. The first step in the invasion probably was the
occupation of southeastern Washington. No barrier prevents mammals from
reaching southeastern Washington from eastern Oregon but the Columbia to
the north and west prevents them from occupying the Yakima Valley, and
the Snake River prevents them from reaching the Columbian Plateau. The
kangaroo rat, Great Basin striped skunk and Great Basin spotted skunk
now are at this stage of invasion. The second stage was the crossing of
the Columbia River to the Yakima Valley. This has been accomplished by
the black-tailed jack rabbit and, earlier, by the pocket mouse,
_Perognathus parvus parvus_, and ground squirrel, _Citellus townsendii_.
The third stage was the crossing of the Snake River and occupation of
the Columbian Plateau. The final stage is the crossing of the northern
Columbia River and occupation of the Okanogan Valley.
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.