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.