Endangered and Threatened Wildlife and Plants; Status Review and
12-Month Finding for a Petition To List the Washington Population of
the Western Gray Squirrel
[Federal Register: June 10, 2003 (Volume 68, Number 111)]
[Notices]
[Page 34628-34640]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr10jn03-78]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
Endangered and Threatened Wildlife and Plants; Status Review and
12-Month Finding for a Petition To List the Washington Population of
the Western Gray Squirrel
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding for a petition to list a distinct population segment
(DPS) of the western gray squirrel (Sciurus griseus griseus) in
Washington, in accordance with the Endangered Species Act of 1973, as
amended. After reviewing the best scientific and commercial information
available, we find that the petitioned action is not warranted because
the petitioned entity is not a DPS and, therefore, not a listable
entity. Additionally, we evaluated the Washington populations of the
western gray squirrel relative to the entire range of the subspecies
and determined that the Washington populations collectively do not
constitute a significant portion of the range of the subspecies. We ask
the public to submit to us any new information that becomes available
concerning the status of or threats to this subspecies. This
information will help us monitor and encourage the conservation of this
subspecies.
[[Page 34629]]
DATES: The finding announced in this document was made on May 30, 2003.
Although further listing action will not result from this finding, we
request that you submit new information concerning the status of or
threats to this subspecies whenever it becomes available.
ADDRESSES: You may send data, information, or questions concerning this
finding to the Manager, U.S. Fish and Wildlife Service, Western
Washington Fish and Wildlife Office, 510 Desmond Drive SE, Suite 102,
Lacey, WA 98503. In order to inspect the petition, the administrative
finding, supporting information, and comments received, you may make an
appointment during normal business hours at the above address.
FOR FURTHER INFORMATION CONTACT: Ken Berg, Manager, Western Washington
Fish and Wildlife Office (see ADDRESSES) (telephone 360/753-9440,
facsimile 360/753-9405).
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act of 1973, as
amended (Act) (16 U.S.C. 1531 et seq.), requires that, for any petition
to revise the List of Threatened and Endangered Species that contains
substantial scientific or commercial information that listing may be
warranted, we make a finding within 12 months of the date of the
receipt of the petition on whether the petitioned action is (a) not
warranted, or (b) warranted, or (c) warranted but precluded by other
pending proposals. Such 12-month findings are to be published promptly
in the Federal Register.
On January 4, 2001, we received a petition dated December 29, 2000,
from the Northwest Ecosystem Alliance, Bellingham, Washington, and the
Tacoma Audubon Society, University Place, Washington. The petition
requested an emergency rule to list the Washington population(s) of the
western gray squirrel (Sciurus griseus griseus) as threatened or
endangered under the Act or, alternatively, the immediate emergency
listing of just the southern Puget Sound population of western gray
squirrels, followed by a later consideration of the ``full Washington
State distinct population segment under the standard processing
requirements.'' On October 29, 2002, we announced an initial petition
finding in the Federal Register (67 FR 65931) concluding the petition
presented substantial information to indicate there may be one or more
distinct population segments (DPS) of western gray squirrels in
Washington for which listing may be warranted. We are making this 12-
month petition finding in accordance with a court order to complete
this finding by June 1, 2003 (Northwest Ecosystem Alliance v. U.S. Fish
and Wildlife Service (CV No. 02-945 KI (D.OR)).
Taxonomy
The western gray squirrel belongs to the mammalian order Rodentia,
the suborder Sciurognathi, and the family Sciuridae. There are three
subspecies of western gray squirrel: Sciurus griseus griseus, which
ranges from central Washington to the western Sierra Nevada Range in
central California; S. g. nigripes, which ranges from south of San
Francisco Bay in the central California Coast Range to San Luis Obispo
County; and S. g. anthonyi, which ranges from the southern tip of the
Coast Range (near San Luis Obispo, California) into south-central
California (Hall 1981). Sciurus griseus griseus was described from a
squirrel seen by Lewis and Clark at The Dalles in Wasco County, Oregon
(Bailey 1936; Hall 1981).
The western gray squirrel is the largest native tree squirrel in
the Pacific Northwest and is the only member of the genus Sciurus
native to Washington. Two other members of the genus found in
Washington are introduced species: the eastern gray squirrel (S.
carolinensis) and the fox squirrel (S. niger) (Washington Department of
Wildlife (WDW) 1993). Other common names applied to this subspecies
include the silver-gray squirrel (Bailey 1936; Booth 1947; Maser et al.
1981), California gray squirrel (Grinnell and Storer 1924; Couch 1926),
Oregon gray squirrel (Bowles 1921), Columbian gray squirrel (Bailey
1936), banner-tail (Scheffer 1923), and gray squirrel (Bowles 1920,
Booth 1947).
Description and Natural History
Western gray squirrels are silvery-gray with dark flanks and creamy
white underneath. The tail is long, bushy, and edged with white; darker
hairs in the tail give it a pepper-gray frost effect. Large ears
without tufts also distinguish the western gray squirrel from other
tree squirrels. There is a light reddish-brown wash on the backs of the
ears, but otherwise the western gray squirrel is entirely gray. To some
extent it resembles the eastern gray squirrel, native to the eastern
United States but introduced into the range of the western gray
squirrel. However, eastern gray squirrels, which are smaller in size,
also have smaller tails and rufous (reddish) coloration on the head,
back, flanks, and underparts (WDW 1993; Carraway and Verts 1994; Ryan
and Carey 1995a).
Body measurements of western gray squirrels can be variable. Adult
weights can range from 18 to 33 ounces (520 to 942 grams). Total
lengths (inclusive of body and tail) may range from 20 to 24 inches
(in) (500 to 615 millimeters (mm)), with tail lengths ranging on
average from 9 to 15 in (240 to 381 mm) and body lengths ranging from
10 to 15 in (265 to 391 mm) (Hall 1981; Carraway and Verts 1994). Based
on the results of four studies, body measurements of western gray
squirrels in Klickitat County, Washington, were found to be
significantly larger than elsewhere in the subspecies' range (Mary
Linders, Washington Department of Fish and Wildlife (WDFW), pers. comm.
2003d).
Western gray squirrels are arboreal (adapted for living in trees)
and, although they forage on the ground, they rarely stray far from
trees. They use tree canopies for escape, cover, and nesting. Western
gray squirrels can move rapidly and cover long distances among tree
canopies when canopy conditions permit. A contiguous tree canopy that
allows arboreal travel for at least 198 feet (ft) (60 meters (m))
around the nest is an important feature of western gray squirrel
habitat (Ryan and Carey 1995a).
Western gray squirrels avoid open spaces; in the Puget Trough,
western gray squirrels will not cross the prairie to use an isolated
tree (Ryan and Carey 1995a). Western gray squirrels, when released from
traps and pointed toward openings, did not cross the prairie or open
areas any larger than about 40 ft (12 m). Movements across relatively
open areas to small groups of trees or small habitat patches can be
facilitated by scattered saplings and small trees in fence lines or in
the open areas. For example, one radio telemetered squirrel was
observed in a group of three isolated trees separated from the main
stand by scattered individual trees. The distance of movement, which is
rapidly completed, across a relatively open area with scattered trees
may be about 150 ft (50 m) (M. Linders, pers. comm. 2003a).
Ryan and Carey (1995b) found that western gray squirrels on Fort
Lewis Military Reservation (Fort Lewis) in Washington were rarely seen
in small (less than 5 ac (2 ha)), isolated pure oak stands or in pure
Douglas-fir (Pseudotsuga menziesii) stands away from oaks. Western gray
squirrels preferred stands with a mixture of conifers, oaks, and other
food-bearing tree species, and were seen most often in stands greater
than 5 acres (ac) (2 hectares (ha)) in size and not more than 1,280 ft
(390 m) away from water.
[[Page 34630]]
In Washington, and elsewhere within the subspecies' range, the
principal food is acorns, although the seeds of Douglas-fir and other
conifers are also eaten (Dalquest 1948). While pine nuts and acorns are
considered essential foods for storing body fat and conditioning
western gray squirrels for winter, green vegetation, seeds and nuts of
trees and shrubs, fleshy fruits, mushrooms, and other foods are also
consumed. Hypogeous fungi (underground fungi such as truffles) comprise
a large portion of the western gray squirrel diet (WDW 1993; Carraway
and Verts 1994; Ryan and Carey 1995a).
The western gray squirrel is in the northern portion of its range
in Washington, where the diversity of mast-producing tree species is
less than in Oregon or California. ``Mast'' includes fruits and nuts
used as a food source by wildlife. A decreased diversity of food
resources increases the likelihood that concurrent mast failures could
seriously affect the survivability of a mast dependent species such as
the western gray squirrel population (Ryan and Carey 1995a, b; Linders
2000).
Western gray squirrels require a year-round source of water. On
Fort Lewis, western gray squirrels select forested stands within 1,800
ft (550 m) of permanent water (Ryan and Carey 1995b). The majority of
nests at one site in Okanogan County, Washington were within 0.6 mile
(mi) (1 kilometer (km)) of water, with a maximum distance of 1 mi (1.6
km) (M. Linders, pers. comm. 2003d). Western gray squirrels drink
freely from permanent and intermittent water sources, including lakes,
marshes, rivers, streams, and puddles (Ryan and Carey 1995a).
Western gray squirrels are active throughout the day, but are most
active in the morning. They were observed from dawn to dusk and year
round on Fort Lewis; no nocturnal activity has been observed. Western
gray squirrels are most active in August and September, when they are
collecting and storing food for winter, and they are less visible in
June and July (Ryan and Carey 1995a).
Home range sizes can differ with age, sex, location, population
density, and from year to year. Home range size increases with social
rank and the number of nests used by an individual. Typically, home
range sizes for western gray squirrels vary across the subspecies'
range from 1.2 ac (0.5 ha) recorded for males in a city park in
California, to 16 ac (6.5 ha) in northern Oregon. Recorded home ranges
of females vary from 0.3 ac (0.1 ha) in California to 42 ac (17 ha) in
Oregon in the summer (Ryan and Carey 1995a). However, a study on the
Klickitat Wildlife Area in Klickitat County, Washington, documented
average home range sizes of 180 ac (73 ha) for males and 52 ac (21 ha)
for females (Linders 2000). These home range estimates from Klickitat
County were significantly larger than in other parts of the subspecies'
distribution. However, methods used to determine home range sizes may
be a source of variability (Ryan and Carey 1995a).
Western gray squirrels use two types of stick nests: large, round,
covered shelter nests are used in winter, and broad platforms are for
seasonal or temporary use (Ryan and Carey 1995a). Cavity nests are also
used for rearing young and for sleeping at other times (Carraway and
Verts 1994). Western gray squirrels frequently use more than one nest,
with different individuals often occupying the same nest on successive
nights; two squirrels rarely occupy the same nest simultaneously
(Linders 2000). Construction and use of multiple nests by individual
squirrels, overlap in use, and the fact that nests may remain intact
for 3 to 5 years makes it difficult to associate the number of nests
with an estimate of the population size. As an example, in Klickitat
County, most pregnant and lactating females used cavity nests in oaks
and averaged 14.3 nests each, significantly more than the 3.5 nests per
squirrel reported for southern Oregon.
Males reach sexual maturity at 1 year and females at 10 to11 months
of age. In western Washington, breeding occurs from January to
September, and lactating females have been observed from May to August
(Ryan and Carey 1995a; M. Linders, pers. comm. 2003d). Most researchers
believe western gray squirrels have only one litter each year, although
there is some indirect evidence to indicate two litters may be
biologically possible, but uncommon (Ryan and Carey 1995a). Litter
counts ranged from one to five, averaging about 2.6 young/litter over a
3-year period (M. Linders, pers. comm. 2003d).
Distribution
Historically, the western gray squirrel's distribution was
widespread throughout Washington, Oregon, California, and in western
Nevada along the base of the Carson Range and in Washoe County
(Dalquest 1948). Currently, the subspecies is rare in Nevada and absent
from the Central Valley in California. Western gray squirrels still
occur in the interior valley margin of the Cascade Mountains in Oregon
and Washington; the foothills of the Coast Range in Oregon; the Sierra
Nevada, Tehachapi, Little San Bernardino, Santa Rosa, and Laguna
Mountains in central and southern California; and westward through the
Coast Ranges of California (Carraway and Verts 1994). In California,
the western gray squirrel is fairly common in the Klamath Mountains of
northern California, and the Transverse and Peninsular Ranges of
southern California (California Department of Fish and Game (CDFG)
1990). In Oregon, the western gray squirrel distribution extends along
the southwestern foothills of the Coast Range northward to Coos Bay,
and north along the eastern side of the Coast Range and along both
sides of the Cascade Mountains into Washington (Verts and Carraway
1998).
Western gray squirrels in Washington once ranged from southern
Puget Sound south to the Columbia River, east along the Columbia River
Gorge in the southern Cascades, and north along the eastern slopes of
the Cascades to Lake Chelan. Documentation for western gray squirrels
includes records for Pierce, Thurston, Grays Harbor, Lewis, Clark,
Skamania, Klickitat, Yakima, Kittitas, Chelan, and Okanogan Counties in
Washington. There is one record from extreme northeastern Whatcom
County, probably associated with western gray squirrels in the northern
Cascade Mountains (WDW 1993; WDFW 2002). Currently in Washington, the
western gray squirrel distribution has been reduced to three
geographically isolated western gray squirrel populations in
Washington: the ``Puget Trough'' population, now centered in Thurston
and Pierce Counties in the Puget Sound region; the ``South Cascades''
population in extreme eastern Skamania County and Klickitat and Yakima
Counties; and the ``North Cascades'' population in Chelan and Okanogan
counties (Bayrak[ccedil]i et al. 2001, WDW 1993). The distribution of
western gray squirrels in each of these counties is limited.
Status Review
On October 29, 2002, we published a positive initial 90-day
administrative finding on the petition to list the Washington
population of the western gray squirrel in the Federal Register
indicating the petitioned action may be warranted (67 FR 65931). At
that time, we requested public comments on this initial finding and any
additional information, comments, and suggestions from the public,
governmental agencies, the scientific community, industry, and any
other interested parties concerning the status of the subspecies
throughout its range in Washington, Oregon, California, and Nevada. We
asked for
[[Page 34631]]
information regarding the subspecies' historic and current
distribution, habitat conditions and use, biology and ecology, threats,
and ongoing conservation measures for the subspecies and its habitat.
We requested any available information on the three Washington
populations of the western gray squirrel concerning (1) the genetics of
these populations as they relate to each other and to the closest
populations in Oregon; (2) the extent to which the two populations east
of the Cascade Mountains are discrete from each other; (3) current
status and trends of each of these populations; (4) the presence of the
subspecies on additional public or private lands; (5) identification of
the current specific threats to each of the populations; and (6) any
additional information supporting the DPS analysis of significance, as
defined in our DPS policy (61 FR 4722), of each of these populations to
the subspecies as a whole.
We received comments, information, and data concerning the status
of the western gray squirrel from 27 individuals, State and local
agencies, nongovernmental organizations, industries, museums, and
universities. Some commenters expressed only support for or opposition
to a potential listing without providing additional documentation.
Information or data from more substantive comments are incorporated,
where appropriate, and concerns raised in the comments are addressed
throughout this petition finding. We also reviewed information from
peer-reviewed journal articles, agency reports and file documents,
telephone interviews, and correspondence with biologists familiar with
the western gray squirrel.
Western Gray Squirrel Status Summary
The rangewide status review initiated in the 90-day petition
finding (67 FR 65931) entailed obtaining and considering the best
scientific and commercial information available to assist us in our DPS
analysis for the western gray squirrel in Washington.
Nevada
Western gray squirrels are considered uncommon in Nevada. They are
only found on the Carson Range in west-central Nevada where they are
yearlong residents; they are not documented to currently occur
elsewhere in Nevada (Biological Resources Research Center, University
of Nevada-Reno (UNR) 2003). Johnson (1954) reported collection of the
subspecies in Washoe County near the California State line, and
observations of individuals along the base of the Carson Range. Hall
(1981) cites marginal records in Verdi and just southwest of Carson
City.
The Nevada western gray squirrel population probably represents a
migrant population from the Sierra Nevada in California on the fringe
of the subspecies' range (UNR 2003). Although western gray squirrels
occur along the west slope of the Sierra Nevada, up to 7,700 ft (2,347
m) at times, they probably crossed into Nevada from lower elevations in
the northern Sierra Nevada. The subspecies has never been wide-ranging
in Nevada, and its limited range in Nevada is probably related to the
absence of oak trees (Johnson 1954).
The western gray squirrel is a ``protected species'' under the
Nevada Administrative Code (NAC) (NAC 503.030). There is no open season
on species classified as protected (NAC 503.090), according to criteria
specified in NAC 503.103. The National Heritage Status Rank for the
western gray squirrel in Nevada is S4 (Apparently Secure) (NatureServe
Explorer 2002).
Current distribution and population sizes in Nevada have not been
documented. Although small and possibly isolated from other populations
in the subspecies' range in California, this western gray squirrel
population has apparently never been large. Two public comments in
response to our request for information in the 90-day finding provided
data suggesting that western gray squirrels are ``common in the Lake
Tahoe basin, especially in the urbanized areas of the basin'' (J. Shane
Romsos, Tahoe Regional Planning Agency (NV), pers. comm. 2002) and are
``common and well-adapted to the urban/forest interface setting in
South Lake Tahoe, California'' (Peter Maholland, California Tahoe
Conservancy, pers. comm. 2002). Western gray squirrels are apparently
adapted to habitat and food sources available in these urbanized areas.
California
The western gray squirrel is fairly common in California where it
occupies mature stands of most conifer, hardwood, and mixed hardwood-
conifer habitats in the Klamath, Sierra Nevada, Tehachapi, Little San
Bernardino, Santa Rosa, Laguna Mountains, and Transverse and Peninsular
Ranges. Western gray squirrels are also found in riparian stands and
other suitable habitats in the Sacramento Valley (CDFG 1990).
The western gray squirrel is a regulated game species in
California. CDFG bases hunting regulations on estimates of
approximately 12 million ha (30 million ac) of western gray squirrel
habitat, not including orchards, that are occupied by approximately 18
million squirrels just before the breeding season. Their estimates
include an average net increase of about 1.2 million squirrels
annually, after assuming a 50 percent juvenile mortality, a 50 percent
adult mortality, and a hunting harvest rate of less than 1 percent each
year. Their conclusions, based on these estimates, are that hunting
mortality does not have adverse effects on the western gray squirrel
populations, and that environmental and density-dependent mechanisms
help keep the populations in check with their habitats (CDFG 2002).
Also, CDFG data indicate the number of tree squirrel hunters has
declined from a high of about 68,000 in the late 1960s to about 12,000
hunters in 2000. The number of tree squirrels harvested has declined
from a peak of about 350,000 in the late 1970s to about 75,000 tree
squirrels harvested in 2000 (CDFG 2002).
The National Heritage Status Rank for the western gray squirrel in
California is S4 (Apparently Secure) and S5 (Secure) (NatureServe
Explorer 2002). None of the subspecies of the western gray squirrel is
included on the CDFG ``special animal'' list. This list is a general
term referring to all of the taxa the California Natural Diversity Data
Base is interested in tracking, regardless of their legal and
protection status (CDFG 1999).
Several conservation programs, policies, and regulations help
maintain western gray squirrel habitat in California. The Integrated
Hardwood Range Management Program, established in 1986, aims to
maintain, and increase where possible, acreage of California's hardwood
range resources. In 2001, the Oak Woodlands Conservation Act created
the Oak Woodlands Conservation Fund for conservation actions to
preserve oak woodlands and guidelines for the program are under
development. The California Forest Practice Rules provide regulations
for maintaining hardwood and riparian components during timber harvest
planning. California Partners in Flight prepared an oak woodland bird
conservation plan to conserve and restore oak woodlands, which will
help maintain western gray squirrel habitats and populations. The 1985
hardwood conservation policy and 1989 hardwood guidelines developed by
the California Fish and Game Commission are used as references to
ensure hardwood conservation measures are considered in all project
proposals reviewed under the California Environmental Quality Act
(Patrick Lauridson, CDFG, in litt. 2002).
[[Page 34632]]
Oregon
There are no historical or current population data for the western
gray squirrel in Oregon, but based on Bailey (1936) and anecdotal
information (Marshall et al. 1996), the numbers and distribution of
western gray squirrels appear to be much reduced. The Natural Heritage
Rank for the western gray squirrel in Oregon is S4? (i.e., the
subspecies is not rare and apparently secure, but with cause for long-
term concern; the ``?'' indicates the assigned rank is uncertain)
(Oregon Natural Heritage Program 2001).
Oregon maintains a list of State threatened and endangered species
under the authority of ORS 496.172, the Oregon Endangered Species Act
of 1987 (OESA) (Oregon Administrative Rule (OAR) 635-100-100 to 635-
100-130), which helps in carrying out the State's policy of preventing
the serious depletion of any indigenous species. Oregon's Sensitive
Species Rule (OAR 635-100-040) requires the Oregon Department of Fish
and Wildlife (ODFW) to develop and maintain a State list of sensitive
vertebrate species that are likely to become threatened or endangered
throughout all or any significant portion of their range in Oregon.
This list was created for the purpose of encouraging actions that will
prevent further declines in species' populations and habitats and avoid
the need for listing under the OESA. The western gray squirrel is
classified by ODFW as a sensitive species of ``undetermined status'' in
Oregon, which indicates the subspecies may be susceptible to population
decline of sufficient magnitude that it could qualify for State
classification as endangered, threatened, critical, or vulnerable
status, but additional research is needed (ODFW 1997; Oregon Natural
Heritage Program 2001). The basis for the western gray squirrel's
sensitive species classification in Oregon includes population declines
caused by timber harvesting and competition with other tree squirrel
species (Marshal et al. 1996). Western gray squirrels are legally
hunted in Oregon. Hunting restrictions that delay and shorten the
hunting season in north-central Oregon, however, help avoid take of
lactating females (Marshal et al. 1996).
Washington
The western gray squirrel was once considered one of the most
commonly encountered mammals in the Pacific Northwest (Bowles 1921).
The western gray squirrel was more widely distributed in prehistoric
times, probably ranging throughout western Washington and the Cascade
Mountains in association with oak communities, but has diminished in
recent times along with the decrease in distribution of oak woodlands
(Rodrick 1987; WDW 1993). One hypothesis suggests that the western gray
squirrel migrated northward into Washington with the spread of Oregon
(Garry) white oak (Quercus garryana) from the Willamette Valley in
Oregon. Dalquest (1948) described the western gray squirrel in
Washington as being a species ``of oak woods rather than coniferous
forest'' with its geographic range largely regulated by the
distribution of oaks, especially Oregon white oak. The range of this
subspecies in Washington, formerly widespread in the oak-conifer
forests, is now less widely distributed and limited to small scattered
populations that follow the range of Oregon white oak (Ryan and Carey
1995a; WDFW 1995).
In Washington, western gray squirrels once ranged from southern
Puget Sound south to the Columbia River, east along the Columbia River
Gorge in the southern Cascade Mountains, and north along the east side
of the Cascade Mountains to Lake Chelan (Booth 1947; Larrison 1970).
During the last century, the western gray squirrel distribution in
Washington has been reduced to three geographically isolated western
gray squirrel populations in Washington: The ``Puget Trough''
population, now centered in Thurston and Pierce Counties in the Puget
Sound region; the ``South Cascades `` population in extreme eastern
Skamania County and Klickitat and Yakima Counties; and the ``North
Cascades'' population in Chelan and Okanogan counties (WDW 1993). The
National Heritage Status Rank for the western gray squirrel in
Washington is S2 (imperiled) (NatureServe Explorer 2002).
There have been relatively few studies of western gray squirrels in
Washington. Early literature was largely observational and anecdotal
(Bowles 1920, 1921; Scheffer 1923; Couch 1926; Dalquest 1948; Larrison
1970). Recent studies to determine western gray squirrel densities,
biology, and ecology have not been consistent in objectives, effort, or
techniques, and have not been directed at determining the status and
trends of the subspecies in all areas of the State.
A regional assessment of the conservation status for potential
western gray squirrel habitat in Washington determined that there are
approximately 1.8 million ac (719,035 ha) of potential western gray
squirrel habitat in the state (M. Linders, pers. comm. 2003d). In the
Puget Trough, there are 1,797 ac (727 ha) of occupied habitat remaining
(David Brittell, WDFW, in litt. 2003). The estimate of ``occupied''
habitat was based on western gray squirrels and nest locations buffered
by a 183-ac (74-ha) circle, the average home range size for male
squirrels in Klickitat County (D. Britell, in litt. 2003). A 1996 model
was developed to direct survey efforts in Klickitat County, where
62,189 ac (25,167 ha) were identified as occupied. However, application
of the buffering method, developed in a later study, to the 1996
potential habitat model indicated there may be only 56,607 ac (22,908
ha) that are occupied in Klickitat County. In Chelan and Okanogan
Counties, 3,094 ac (1,252 ha) were identified as occupied (Cassidy et
al. 1997; D. Brittell, in litt. 2003).
Puget Trough Population. Bowles (1920, 1921) stated that western
gray squirrels were in the Puget Trough as early as 1896, although ``by
no means common'' at that time, probably because of adverse
environmental conditions and lack of legal protection. He suggested
that western gray squirrels had always been in Pierce County in low
numbers, traveling up from Oregon over time and becoming permanent
residents if food and other natural conditions were satisfactory.
Bowles reported that following legal protection about 1910, there was
an ``immense increase'' in numbers of western gray squirrels. By 1921,
there was significant damage to trees caused by western gray squirrels
stripping bark for food in the Pierce County area. Squirrel hunting was
reinstated in 1926 and continued until 1943, except for a localized
hunt in Thurston and Pierce Counties in 1949 and 1950. The western gray
squirrel became a State protected species in 1954. Although records
show that western gray squirrels still occurred in the Puget Trough in
the 1970s and 1980s, they had become increasingly rare and were found
only in isolated relict populations restricted to a few locations in
the state (Rodrick 1987, WDW 1993, WDFW 2002).
Current population estimates of the western gray squirrel in the
Puget Trough area are limited. In southern Thurston County, the last
western gray squirrel was seen in the late 1970s (WDFW 2002). Surveys
during 1985 and 1986 detected western gray squirrels on just 4 of 26
sites (15 percent), and these were confined to the Fort Lewis area
(Rodrick 1987). In Statewide surveys of 40-ac (16-ha) survey blocks
from 1994 to 2000 by WDFW, western gray squirrels or nest locations
were found in 9 of 100 (9 percent) survey blocks in the Puget Trough.
In February 1996, no
[[Page 34633]]
western gray squirrels were detected in WDFW surveys in Thurston County
(D. Brittell, in litt. 2002). Isolated occurrences have been reported
in the past in Grays Harbor and Lewis Counties (WDFW 2002), and more
recently in Clark County (Tracy Fleming, National Air and Stream
Improvement Council, pers. comm. 2003). In 2002, fewer than a dozen
sightings of western gray squirrels were reported (Dave Clouse, Fort
Lewis, pers. comm. 2003).
Although the western gray squirrel was once common on the partially
wooded prairies adjacent to Puget Sound, the surviving Puget Trough
population is now centered on Fort Lewis in southern Pierce and
northern Thurston Counties where the largest area of oak woodlands
remains. From 1992 to 1993, 156 western gray squirrel observations were
documented on 169 sites on Fort Lewis. These observations were
estimated to represent 81 individual western gray squirrels on 44 oak-
conifer sites (Ryan and Carey 1995b). During intensive surveys in 1998
to 1999, only 6 western gray squirrels in only 4 percent (5 of 133)
suitable habitat stands were detected in over 4,000 hours of survey
effort. The researchers concluded that the low western gray squirrel
population on Fort Lewis is at a high risk of extirpation
(Bayrak[ccedil]i et al. 2001). Subsequent western gray squirrel
sightings included 3 (including 1 road kill) in 2000 and 11 (including
1 road kill) in 2002 (D. Clouse, pers. comm. 2003). Factors that may
have influenced the decline of western gray squirrels on Fort Lewis
include (1) poor acorn crops or undependable food resources; (2)
drought and unavailability of water in many oak ecotones; (3) road
kills; (4) competition with eastern gray squirrel and Douglas'
squirrels (Tamiasciurus douglasii); (5) reduction in quality and
quantity of oak habitat; (6) diseases and parasites; and (7) predation
(Carey and Harrington 2001).
From 1993 to 1995, The Nature Conservancy of Washington conducted
surveys, analyzed nest trees, and trapped western gray squirrels on
McChord Air Force Base (McChord AFB) adjacent to Fort Lewis. Fifteen
observations of western gray squirrels occurred at 6 different
locations on McChord AFB. Most of these observations (13) occurred in
1993, with the remaining two observations occurring in 1995; none were
observed in 1994 (The Nature Conservancy of Washington and Washington
Natural Heritage Program 1996). They hypothesized that western gray
squirrels were dispersing from Fort Lewis to McChord AFB to use acorns
and other food resources when available, but only when environmental
conditions were favorable (e.g., when water sources are available in
wet years). In the mid-1990s, a western gray squirrel occupied a nest
box erected for American kestrels (Falco sparverius) on McChord AFB.
Two or three western gray squirrels were seen in 1995, and possible
western gray squirrel nests were found in 1996 (McChord AFB 2002).
Although western gray squirrels were previously found on private lands,
the last observation of western gray squirrels on private lands
adjacent to the military bases was in 1990 (WDFW 2002).
The western gray squirrel in the Puget Trough of western Washington
persists in a transitional ecological setting, in comparison with the
subspecies' populations elsewhere in its range. Western gray squirrels
in the Puget Trough occupy an ecotone (transitional) habitat composed
of Oregon white oak woodlands situated between upland Douglas-fir
forests and prairies (Ryan and Carey 1995; Bayrak[ccedil]i et al.
2001). Here, scattered woodlands of Oregon white oak and Douglas-fir
encircle the prairies (WDW 1993).
This western gray squirrel population, located at the northwestern
limits of the subspecies' range, occur in habitat that closely conforms
to the distributional range of the Oregon white oak. The western gray
squirrel ranges only as far north in the Puget Trough as the northern
limit of the continuous distribution of Oregon white oak on the
gravelly prairies just south of Tacoma (Dalquest 1948; Larrison 1970;
Stein 1990; WDW 1993). While the Puget Trough area is essentially the
northwestern limit of the continuous range of the Oregon white oak, it
does occurs in discontinuous patches further north on the islands of
Puget Sound and, in British Columbia, Canada, on Vancouver Island and
in two disjunct stands on the mainland (Stein 1990).
Geologic and floristic evidence indicates that Oregon white oak
associations have evolved through successive eras as components of
relatively arid pine forest that repeatedly advanced northward from a
locus in the southwestern U.S. and northwestern Mexico as climates
warmed and retreated as climates cooled. The most recent northward
expansion ended about 6,000 years ago (Stein 1990). Pollen spectra
samples show that oak communities were common around Puget Sound during
the warm, dry post-glacial period 10,000 years ago. Subsequent trends
toward cooler and moister conditions have influenced the replacement of
Oregon white oaks by conifers (Stein 1990; Agee 1993; WDW 1993).
Prehistorically, the ``Tacoma prairies'' once occupied the lowland
areas of Pierce and Thurston Counties in the Puget Sound region of the
Puget Trough, with a southward finger into Lewis County; prairies
intermittently reappeared in Clark County down to the Columbia River
(Kruckeberg 1991). This landscape feature of the Puget Trough consists
of a mosaic of prairie, oak woodland, and open forest called a
``gravelly outwash plain.'' The gravelly outwash prairies coincide with
the southern terminus of the last continental ice sheet during the
Vashon glaciation, which ended 15,000 years ago (Kruckeberg 1991).
Although the Puget Trough of western Washington has a wetter
climate than occurs in much of the Oregon white oak range, the Puget
Sound area is near sea-level and has a warm, relatively dry climate
because of the Puget Sound and the surrounding mountain ranges (Thysell
and Carey 2001). The Puget Sound region is included in the Tsuga
heterophylla (western hemlock) Zone, with many of the same plant
communities. Large areas in this region, however, differ from the
surrounding plant community types in that prairie, oak woodland, and
pine forest are encountered. These plant-community type differences,
related to both climate and soil, include Oregon white oak stands and
prairies being invaded by Douglas-fir and the occurrence of species
rarely or never found in western Washington or northwestern Oregon
(Franklin and Dyrness 1988).
As previously discussed, western gray squirrels depend primarily on
acorns and pine seeds (Sumner and Dixon 1953; Kruckeberg 1991; Carraway
and Verts 1994). Because of the wetter climate and flatter topography
of the Puget Trough in comparison with the rest of the western gray
squirrel range, the habitat is more homogeneous, and there are fewer
mast-producing trees (C. Maser, pers. comm. 2003). Consequently, in
this region, the success of the western gray squirrel is probably more
intimately tied to the success of Oregon white oak because it provides
an essential winter food item for this squirrel.
Elsewhere in the subspecies' range, Oregon white oaks occur in
communities that include a wider range of mast-producing tree species.
In western Washington, the western gray squirrel depends primarily on
Oregon white oak, Douglas-fir, and where available, ponderosa pine
(Pinus ponderosa). In Oregon, the western gray squirrel diet includes
seeds from a
[[Page 34634]]
wider variety of oak (i.e., Oregon white oak, tanoak (Lithocarpus
densifloris), Sadler oak (Quercus sadleriana), canyon live oak (Quercus
chrysolepis), California black oak (Quercus kelloggii), valley oak
(Quercus lobata) and pine species (i.e., sugar pine (Pinus
lambertiana), Jeffrey pine (Pinus jeffreyi), lodgepole pine (Pinus
contorta) than are available to western gray squirrels in the Puget
Trough of Washington (Carraway and Verts 1994; Marshall et al. 1996).
In California, the western gray squirrel is dependent on mature
stands of conifer and oak habitats and is closely associated with oaks
(CDFG 1990). Oak species in western gray squirrel habitat in California
include valley oak (Quercus lobata), blue oak (Quercus douglasii),
California black oak, interior live oak (Quercus wislizenii), and scrub
oak (Quercus dumosa). In addition to Douglas-fir and ponderosa pine,
other tree species in California western gray squirrel habitats include
Fremont cottonwood (Populus fremontii), digger pine (Pinus sabiniana),
white fir (Abies concolor), sugar pine, giant sequoia (Sequoiadendron
giganteum), redwood (Sequoia sempervirens), and eucalyptus (Eucalyptus
globulus) (Carraway and Verts 1994).
Although western gray squirrels consume hypogeous fungi and seeds
and nuts of various trees and shrubs, acorns and pine seed may be more
critical in the diet because they are high-energy foods needed for
overwintering (Ryan and Carey 1995a). In the Puget Trough, acorns are
the principal diet from late summer through early spring. Mushrooms and
truffles are mostly eaten in spring and fall, and Douglas-fir seed are
eaten upon ripening in the late summer through fall. However, mast
crops differ each year caused by the depletion of food reserves in a
heavy seed year, weather in year of fruiting or previous years,
diseases and parasites, and maturation differences among tree groups
(Ryan and Carey 1995a). Oak mast production is sporadic and
unpredictable, with good mast years occurring only once in 7 to 10
years. During an 8-year study in northern Oregon, there were 4 years
with poor Oregon white oak acorn crops. In 1991, there was no acorn
crop in the Columbia River Gorge and an insignificant crop in 1992.
When ponderosa pine is not available, western gray squirrels also rely
on Douglas-fir seed (WDW 1993). However, environmental factors make the
Douglas-fir seed crop erratic, and abundant crops are produced
sporadically, from 2 to 11 years apart. One crop failure and two or
more light to medium crops usually occur between heavy crops (U.S.
Forest Service 1974).
South Cascades Population. Although Booth (1947) noted that western
gray squirrels were uncommon in the southern part of the Cascade
Mountains and more common in Pierce County, the South Cascades
population currently is the largest remaining population of western
gray squirrels in Washington. The western gray squirrel appears to be
widely distributed across Klickitat County, but the populations are
localized. Western gray squirrels remain along the Klickitat River and
Catherine, Major, and Rock Creeks (WDW 1993). Between 1994 and 1996,
systematic field surveys to delineate western gray squirrel
distribution in the Columbia River Gorge documented the presence of
individuals or their sign (e.g., nests) in 22 watershed administrative
units. Surveys were conducted in parts of 275-square mi (712-square km)
sections containing suitable western gray squirrel habitat; their
presence was recorded in 61 percent of these sections (M. Linders,
pers. comm. 2003d).
Based on intensive and widespread surveys in Washington from 1994
to 2000, 89 percent (1,642 of 1,847) of all western gray squirrel nests
and observations occurred in Klickitat County (D. Brittell, in litt.
2002). Eighty-three percent (514 of 618) of the occupied survey blocks
had nest locations alone, and 10 percent (59 of 618) of the survey
units had both western gray squirrels and their nests. The 7 percent
(45 of 618) of the survey units having western gray squirrels with no
known nest locations may have represented dispersal or breeding
movements. Nest-only sites likely had associated western gray
squirrels. Because nests persist for several years, however, a die-off
would be difficult to detect (D. Brittell, in litt. 2002). More recent
information is limited to forest practice surveys and random
encounters. Residents noticed a decline of western gray squirrels in
Klickitat County, particularly following introduction of California
(Beechey's) ground squirrels (Spermophilus beecheyi) (Rodrick 1987; WDW
1993).
Statewide surveys from 1994 to 2002 established that most
observations of western gray squirrels and their nests occurred in
Klickitat County (M. Linders, pers. comm. 2003c). Surveys in 2000 and
2001 on the Klickitat Wildlife Area documented density estimates of
0.08-0.13 western gray squirrels/ha and a more recent estimate for
western gray squirrels in this area was slightly higher (0.1-0.2
squirrels/ha) (M. Linders, pers. comm. 2003b). Density estimates for
western gray squirrels in California ranged from 1.37/ha in the spring
in Lake County to 2.47/ha in the Yosemite Valley (Grinnell and Storer
1924). There are no density estimates for western gray squirrels in
Oregon or Nevada.
Booth (1947) described the western gray squirrel as uncommon in the
southern Cascade Mountains. In Yakima County, western gray squirrels
were abundant in the Ahtanum and Cowiche Creek drainages, and less
common along Oak Creek prior to the 1950s. A mange epidemic in the
1940s and 1950s decimated western gray squirrel populations (Stream
1993). Western gray squirrels may have been extirpated from the Oak
Creek Management Area following a severe mange epidemic in the 1940s
and 1950s; a reintroduction attempt in the area, using western gray
squirrels from Oregon, was not successful (WDW 1993).
Little is known about western gray squirrels on the Yakama Indian
Nation Reservation. Between 1995 and 1998, the Yakama Indian Nation
conducted limited surveys across the reservation. Small nest clusters,
scattered individual western gray squirrels, and negative surveys were
reported (D. Brittell, in litt. 2002).
North Cascades Population. The North Cascades population has
received the least attention of the three Washington populations; no
population or trend data, including density estimates, are available.
There were no systematic attempts to delineate the distribution of
western gray squirrels in the North Cascades prior to 1995. During 1995
surveys by WDFW on the west side of the Methow Valley of Okanogan
County, 21 western gray squirrels (including 3 killed by automobiles)
and 2 nests were observed. In 1996, 22 western gray squirrels,
including roadkills, and 89 nests were observed. No western gray
squirrels were observed during surveys of the east side of the Methow
Valley in 1997. When interviewed, residents of the upper Methow Valley
believed that numbers of western gray squirrels were declining, but
residents of the lower Methow Valley thought the populations had been
stable over the past 15 to 30 years (M. Linders, pers. comm. 2003d).
In 2000, surveys of all areas previously known to have western gray
squirrel nests detected only 3 remnants out of the 89 nests recorded in
a 1996 survey (M. Linders, pers. comm. 2003d). Eighteen previously
unreported nests were documented and four western gray squirrels were
observed. Relocating individual nests, however, can be difficult
without detailed mapping and marking (Vander Haegen et al. 2003). Also,
western gray squirrels build and
[[Page 34635]]
use more than one nest per season, and nests may remain intact for 3 to
5 years. Consequently, the fact that only 3 remnant nests and 18
previously unreported nests in an area that formerly had 89 nests may
represent a significant reduction in the number of western gray
squirrel nests in the Methow Valley, possibly suggesting a
corresponding population decline. Additional nest surveys in Chelan
County, not previously surveyed, located seven previously unreported
nests, three western gray squirrels, and one western gray squirrel skin
(no body) (M. Linders, pers. comm. 2003d).
The North cascades population occurs in an ecological setting that
differs from the Puget Trough area. The native range of oaks extended
only into southeastern Yakima County with a patchy distribution in
central Yakima County, central Kittitas County, and northeastern Pierce
County (Stein 1990). The range expansion northward from Yakima County
required adaptations to habitats lacking oaks, the main source of
winter foods for this subspecies in most of its range.
Couch (1928) describes the range of the ``silver gray squirrel'' as
being known from Goldendale (Klickitat County) to Lake Chelan (Chelan
County). Taylor and Shaw (1929) describe the range of the western gray
squirrel as ranging along the eastern edge of the Cascades north to
Lake Chelan. There are verified (reported by reliable biologists or
other knowledgeable individuals) western gray squirrel sightings
recorded for Chelan County from 1938 in the WDFW Natural Heritage
Database (WDFW 2002). Booth (1947) notes records from Lake Chelan.
Larrison (1970) describes the range as including the lower east slopes
of the Cascades to Lake Chelan. He also notes that, while western gray
squirrels are most numerous in the oak woods, they are spotty and
scarce elsewhere in their range.
The western gray squirrel range extension into Okanogan County may
have occurred in response to groves of English walnut (Juglans regia)
and black walnut (J. nigra) planted during the 1940s and 1950s (WDW
1993). Stream (1993) conducted interviews, compiled data from WDW
wildlife data printouts, literature reports, and old files from the WDW
Yakima Regional office and concluded that the western gray squirrel was
native to the east slopes of the Cascade Mountains. He notes that there
was ``apparently a native population in Chelan County, especially
around Lake Chelan,'' but that the documentation was not clear.
Although the predominant habitat used by western gray squirrels was the
oak/pine associations in Yakima County, the oak association was not
found where the western gray squirrels occurred around Lake Chelan. The
interviews revealed that English walnut trees were planted from 1915 to
1920, and by the 1940s, the western gray squirrel was expanding its
range northward due to these planted mast-producing trees. By the
1960s, western gray squirrels were showing up in canyons where black
walnut trees were planted in the 1940s.
Western gray squirrels were present at Lake Chelan at least as
early as the 1920s, and may have been expanding northward before mast-
producing trees planted in nut orchards began producing. Their
secretive behavior and low population densities may have made them hard
to see. Although the nut orchards probably stimulated the northward
expansion and helped population sizes increase, western gray squirrels
were also found in natural habitats. Western gray squirrels were
regularly seen on Chelan Butte (southeast side of Lake Chelan) in the
1960s and in Purtteman Gulch (northeast end of Lake Chelan), but were
no longer found there after fires burned the habitat. In the late
1960s, a western gray squirrel nest was found on a pine tree branch in
Ribbon Cliff Canyon (along the Columbia River north of Entiat). Western
gray squirrels were using pine trees and bigleaf maples (Acer
macrophyllum) for food. A few western gray squirrels were found in
Stehekin (northwestern end of Lake Chelan in Chelan County), but could
not survive because of the harsh weather (Mil Sharp, retired WDW
wildlife agent, pers. comm. 1992, as cited in Stream 1993).
Distinct Population Segment Review
Under the Act, we must consider for listing any species,
subspecies, or any distinct population segments of vertebrates if
sufficient information exists to indicate that such action may be
warranted. We, along with the National Marine Fisheries Service
(National Oceanic and Atmospheric Administration-Fisheries), developed
a joint policy that addresses the recognition of DPS for potential
listing actions (61 FR 4722). The policy allows for more refined
application of the Act that better reflects the biological needs of a
part of the taxon being considered, and avoids inclusion of entities
that do not require the Act's protective measures.
Under our policy, we use two elements to assess whether a
population segment under consideration for listing may be recognized as
a DPS. These elements are (1) discreteness of the population segment in
relation to the remainder of the species to which it belongs; and (2)
the significance of the population segment to the taxon to which it
belongs. If we determine that a population segment being considered for
listing meets the discreteness and significance standards, then the
level of threat to that population segment is evaluated based on the
five listing factors established by the Act to determine if listing the
population segment as either threatened or endangered is warranted.
Under current conditions, the Washington population of the western
gray squirrel consists of three isolated, disjunct populations. The
three populations resulted from western gray squirrels moving
northward, from the region that is now the State of Oregon and later
became separated from more southern populations by the Columbia River.
The distribution of the western gray squirrel in Washington once
extended from south Puget Sound, east along the Columbia River, and
northward to Lake Chelan and subsequently expanded northward into
Okanogan County in more recent times. We view these three populations
as isolated portions of a once-continuous population, with a common
evolutionary history.
Discreteness
A population segment of a vertebrate species may be considered
discrete if it satisfies either one of the following two conditions:
(1) it is markedly separated from other populations of the same taxon
as a consequence of physical, physiological, ecological, or behavioral
factors (quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation); or (2) it is
delimited by international governmental boundaries within which
significant differences in control of exploitation, management of
habitat, conservation status, or regulatory mechanisms exist.
On the basis of available information, we conclude that the
Washington population segment of the western gray squirrel may be
discrete in relation to the remainder of the subspecies' populations
because it appears to be physically separated from other populations to
the south in Oregon, California, and Nevada as a result of geographical
isolation by the Columbia River. Additionally, each of the three
Washington populations appear to potentially be discrete from each
other and this is supported by preliminary genetic analysis (Warheit
(2003)). The Columbia River has likely been a barrier
[[Page 34636]]
to movement and genetic flow for at least 13,000 years (Mercer and Roth
2003), as discussed further below.
Significance
Under our DPS policy, once we have determined that a population
segment is discrete, we consider its biological and ecological
significance to the larger taxon to which it belongs. This
consideration may include, but is not limited to (1) evidence of the
persistence of the discrete population segment in an ecological setting
that is unique for the taxon; (2) evidence that loss of the population
segment would result in a significant gap in the range of the taxon;
(3) evidence that the population segment represents the only surviving
natural occurrence of a taxon that may be more abundant elsewhere as an
introduced population outside its historic range; and (4) evidence that
the discrete population segment differs markedly from other populations
of the species in its genetic characteristics.
Ecological Setting. The western gray squirrel in the Puget Trough
of western Washington persists in a transitional ecological setting,
where it occupies habitat composed of Oregon white oak in an ecotone
(transitional) between upland Douglas-fir forests and prairies, in
comparison with the subspecies' populations elsewhere in its range
(Ryan and Carey 1995; Bayrak[ccedil]i et al. 2001). Consequently,
existence of the western gray squirrel in the Puget Trough is more
intimately tied to the success of Oregon white oak: Oregon white oak is
the only native oak in Washington (Stein 1990) and provides an
essential winter food item for this squirrel (Sumner and Dixon 1953;
Kruckeberg 1991; Carraway and Verts 1994). Acorns and pine seed are
critical high-energy foods needed for overwintering (Ryan and Carey
1995a). In western Washington, western gray squirrels have adapted to a
more homogeneous environment with fewer and less reliable food
resources (Oregon white oak, Douglas-fir, and some ponderosa pine),
particularly relying on the acorn of a single tree species as its
essential storable winter food resource, thus occupying a less
suitable, marginal habitat. Elsewhere in the subspecies' range, Oregon
white oaks occur in communities having a wider range of mast-producing
tree species, including a variety of oak and pine species, which allows
western gray squirrels to use different food resources when one food
resource has a poor year for mast production.
The North Cascades population found east of the Cascade Mountains
also persists in an ecological setting which differs from the Puget
Trough and the South Cascades. In this population, western gray
squirrels expanded their distribution into areas beyond the native
range of Oregon white oak. The presence of western gray squirrels in
Chelan County early in the twentieth century (Couch 1928; Booth 1947;
Larrison 1970; Stream 1993; WDFW 2002) indicates adaptations to using
other food resources. The continuous distribution of Oregon white oak
extended into Yakima County, with only a spotty distribution into
Kittitas County (Stein 1990). The range expansion northward from Yakima
County required occupying habitats lacking oaks that provided the main
winter food for the subspecies, relying on ponderosa pine as the
primary food.
The Washington populations of western gray squirrels are found in
differing ecological settings within the State. However, it is not
clear that they should collectively or independently be considered as
unique ecological settings for the taxon. For example, while the
grasslands and oak woodlands of the Puget Sound area have different
vegetation complexes compared to the grasslands and oak woodlands where
western gray squirrels are found in northern California or southern
Oregon, these differences are not so great that we consider the habitat
of the Puget Sound population to be a unique or unusual ecological
setting for western gray squirrel. The South Cascades population shares
many habitat features common to the habitat for western gray squirrels
found in Oregon. The North Cascades population's habitat is notable in
its absence of oaks, the main source of winter foods for this
subspecies in most of its range. This population appears to rely on the
seed of pine trees and bigleaf maples (Acer macrophyllum). Throughout
their range, however, western gray squirrels consume a variety of types
of tree seeds, including many conifer species. In summary, we do not
find that the Washington populations individually or collectively are
located in an ecological setting unusual or unique for the taxon, such
that they meet the significance criterion of the DPS policy.
Gap in the Range. The Washington population segment of the western
gray squirrel is at the northern portion of the historic and current
distribution of the subspecies. Within the Washington population
segment, the Puget Trough population represents the northwestern
extension, and the North Cascades population represents the
northeastern extension of the subspecies' range.
Within the distribution of every species there exists a peripheral
population, an isolate or subpopulation of a species at the edge of the
taxon's range. The population is the basic evolutionary and ecological
functional unit. The local population is where responses to
environmental challenges occur, where adaptations arise, and where
genetic diversity is maintained and reshuffled each generation. A
species can continue to exist even though many of its populations are
destroyed, resulting in a loss of biodiversity and what may be unique
genetic or phenotypic traits (Meffe et al.1997). Peripheral populations
are often located at a species' ecological limits where unique genetic
combinations are exposed to and tested by environmental circumstances
that may not be found elsewhere in the range of the species. When a
peripheral population is isolated from gene flow from other
populations, the isolated peripheral population may become highly
adapted to local conditions. Distinctive traits found in peripheral
populations can be important for the survival and evolution of a
species as a whole (Meffe et al. 1997).
Long-term geographic isolation and the loss of gene flow between
populations is the foundation for genetic changes in populations
resulting from natural selection or chance. Evidence of changes in
peripheral populations may include genetic, behavioral and/or
morphological differences from populations in the rest of the
subspecies' range. Ecological differences were described above, and
genetic differences in western gray squirrels are discussed below. We
also considered information regarding morphological and behavioral
differences in regard to adaptations that may be occurring in the
western gray squirrel in Washington.
The secretive behavior of the western gray squirrel in Washington
has been frequently noted and might represent an adaptation of a
population on the periphery of its range. Bowles (1921) wrote,
regarding western gray squirrels in Pierce County, Washington, that
``although extremely numerous, we may walk for days in the country they
inhabit and never see one.'' Scheffer (1923) indicated that in the more
heavily timbered country in Washington, the gray squirrel was only
occasionally seen. Couch (1926) noted that, although western gray
squirrels are hard to see, the presence of western gray squirrels in
the lower Puget Sound region is evident in the peeled bark of Douglas-
fir. Larrison (1970) wrote that western gray squirrels in Washington
are ``rather shy and do not mix well with civilization,'' and in the
few places
[[Page 34637]]
where they have entered settled areas it ``keeps hidden from the
watcher.'' During surveys on McChord AFB, observers noted that western
gray squirrels often fled from the presence of the observer (The Nature
Conservancy of Washington and Washington Department of Natural
Resources (WDNR) 1996). More recently, researchers conducting surveys
on Fort Lewis described western gray squirrels as ``very wary and
challenging to approach and therefore can be difficult for observers to
detect'' (Bayrak[ccedil]i et al. 2001).
In Oregon, although described as ``shy and retiring'' in the
countryside where they have little human contact, western gray
squirrels can be found in urban parks where they are more tolerant of
human contact (Susan Weston, in litt. 2003). Along the Nevada/
California border, western gray squirrels appear to be well-adapted to
the urban-forest interface (P. Maholland, pers. comm. 2003) and have
been reported as common in the Lake Tahoe basin, especially in the
urbanized areas (J.S. Romsos, pers. comm. 2003).
Whether the western gray squirrels in Washington are more secretive
than those elsewhere in the range of the subspecies is unclear.
Although evidence of shy behavior of the western gray squirrel has long
been documented for the Washington population, similar behavior has
been documented in Oregon (Susan Weston, in litt. 2003). We believe
this behavior may be consistent with a species at the edge of its
range, where the amount of habitat is restricted by fragmentation and
may be less than optimum, and that rather than being ``shy,'' they are
difficult to observe and maintain a close affinity with the habitat
that remains. The observation of western gray squirrels in towns in
Oregon and Nevada may also be an artifact of there being larger
populations of squirrels in this portion of the subspecies' range. The
differences between rural and urban communities may also be less
distinct in Oregon and Nevada, with the rural characteristic of large
Oregon white oak or ponderosa pine trees or possibly other planted nut
trees providing suitable habitat for the squirrels in the urban
environment.
Overall, much of the available information on ``secretiveness'' of
the subspecies is anecdotal in nature and there are no comparative
studies to determine whether real behavioral differences in
secretiveness exist across the range of the subspecies. Even if such
differences do exist, the reasons for them are not clear, including
whether or how such behavior might be related to the periphery of the
range. The significance of such differences, if they exist, also is
unclear.
In evaluating potential differences in the subspecies at the
northern extent of its range, we also considered information on
morphology and home range size. Body measurements of western gray
squirrels in Klickitat County, Washington, were found to be
significantly larger than elsewhere in the subspecies' range (M.
Linders, pers. comm. 2003d). This study was conducted in a small area
of Klickitat County and results were compared to another study in
Washington with a small sample size, and with two California studies.
Based on the limited area studies and the small sample size, the
results may not be conclusive and applicable for western gray squirrels
over their entire range. We also considered information showing that
western gray squirrels on the Klickitat Wildlife Area have
substantially larger home range sizes when compared with home range
estimates elsewhere in the subspecies' distribution. In this same
study, western gray squirrels also used significantly more nests per
squirrel than recorded for the subspecies in Oregon (Linders 2000).
These results, while interesting, do not explain the reasons for the
differences in home range size and numbers of nests. The limited sample
size is a confounding factor in interpreting these results. Also, as
noted above, differences in methods used to determine home range sizes
may be a source of variability in results among studies (Ryan and Carey
1995a). Many factors could account for these differences, and we have
no basis for concluding that these results should be attributed to the
location of the study area at the northern periphery of the range of
the subspecies. Consequently, we do not believe that the information
concerning morphology, home range size, or number of nests described
for western gray squirrels in Klickitat County provides a justification
for a determination of significance under the DPS policy.
The importance of peripheral populations in relation to climate
change is a continuing source of discussion and study in the scientific
community. Species' ranges can change dramatically with global shifts
in climate. Peripheral populations may survive in isolated refugia that
later, with different environmental conditions, serve as a source
population for an expanded range and subsequent radiation. What
constitutes a peripheral population today could be the center of a
species' range in the future, and consequently peripheral populations
are vitally important to a species' past, present, and future existence
(Nielsen et al. 2001).
We have considered the extent to which western gray squirrels in
Washington may be significant in relation to climate change. As the
result of a climate shift, as occurred in the past when Oregon white
oaks moved northward from Oregon, the northern limits of the western
gray squirrel range could expand northward as the changing climate
again favors Oregon white oak distribution over conifer distributions.
At this time there is speculation, but no clear evidence, of the
potential role that western gray squirrels in Washington might play in
relation to the rest of the subspecies in response to climate change.
Similarly, the nature and extent of the effects of climate change on
ecological conditions for the western gray squirrel in Washington are
not known. Based on the speculative nature of the situation involving
the western gray squirrel in relation to climate change, we do not have
a basis for concluding that a potential gap in the distribution of
western gray squirrels at the northern extent of its range would have
evolutionary implications for the subspecies in relation to the
potential effects of climate change.
Lastly we consider whether the potential reduction in the range of
the subspecies that could occur in the event of the hypothetical loss
of the Washington populations, collectively or individually, would meet
the significance criterion of the DPS policy. Individually, we do not
find that the loss of range that would be represented by the loss of
any of the current Washington populations meets the significance
criterion of the DPS policy. The limited population information
available makes a determination about potential significance
particularly difficult, but when viewed individually we do not see the
potential reduction in range of each population as reaching
significance to the subspecies. Collectively, the loss of all of the
Washington populations would represent a serious reduction in the
species range. However serious such a hypothetical reduction might be,
we do not have information currently that demonstrates this
consideration would meet the DPS policy's requirement of significance
to the taxon (subspecies) as a whole, since there is only limited
information on the potential biological and ecological significance for
Washington in terms of range of the subspecies.
Whether the Population Represents the Only Surviving Natural
Occurrence of the Taxon. As part of a determination
[[Page 34638]]
of significance, our DPS policy suggests that we consider whether there
is evidence that the population represents the only surviving natural
occurrence of a taxon that may be more abundant elsewhere as an
introduced population outside its historic range. The western gray
squirrel in Washington is not the only surviving natural occurrence of
the subspecies. Consequently, this factor is not applicable to our
determination regarding significance.
Marked Differences in Genetic Characteristics. The DPS policy
suggests that one measure of significance is evidence that the discrete
population segment differs markedly from other populations of the
subspecies in its genetic characteristics. Preliminary evidence of
genetic variation among the three western gray squirrel populations in
Washington and two populations in Oregon showed that genetic
variability may exist (Parametrix, Inc. 1999). The sample sizes,
however, were too small for substantive conclusions (M. Linders, pers.
comm. 2003d).
In 2003, researchers from WDFW and the University of Washington
completed genetic analyses, using standard conservation genetic
research techniques, the results point towards significant genotypic
differentiation between Washington populations and squirrel populations
south of the Columbia River. The report presents the results of two
different types of genetic analyses (microsatellite DNA analysis and
mitochondrial control region sequence analyses). The following
discussion of the results of the genetic analyses is summarized from
Warheit (2003).
Microsatellite DNA Analysis
Microsatellite DNA analyses were completed on samples from 128
western gray squirrels from California (3), Oregon (24), and Washington
(101). Samples were obtained from museum skins, museum tissue
collections, road-killed individuals, and ear punches from live-trapped
individuals.
Microsatellites are short (no longer than six base pairs
(nitrogenous bases that are part of the DNA molecule, such as cytosine
and guanine)) tandemly repeated segments interspersed throughout the
chromosome. Changes in the repeats result in different lengths of DNA,
and a specific length of DNA can be used as a marker for a
microsatellite locus (position on the chromosome). Seven of these loci
that showed variation were analyzed. The results of the microsatellite
analysis was summarized by the genetic diversity (the variation in
chromosomes) and the genetic differentiation (how different genetically
are the populations).
Genetic Diversity
? An allele is a series of two or more different genes that
occupy the same position on a chromosome. All populations in Oregon and
California showed at least three private alleles (alleles present in
only that population), while no Washington population had a private
allele. This indicates that while all alleles present in each of the
Washington populations are also present in at least one of the Oregon
or California populations, there are alleles present in either Oregon
or California that are not present in Washington.
? The Washington populations show reduced genetic diversity
at all measures compared with populations south of the Columbia River,
despite the fact that the mean sample size per locus is larger for each
of the Washington populations.
? The reduction in genetic diversity within the Washington
populations may be a function of genetic drift, which in turn may be
the result of relatively smaller effective population sizes in
Washington compared with that in Oregon and California.
Genetic Differentiation
? There is significant differentiation between each of the
Washington populations, and the Oregon and California populations.
? These data support the hypothesis that each of the
Washington Western Gray Squirrel populations are genetically distinct
from each other, and are now functioning as separate and isolated
populations.
? What these analyses demonstrate is that there is
considerably more genetic differentiation between Washington and Oregon
or California, than there is between Oregon and California populations.
Mitochondrial Control Region Sequence Analyses
A subset (67) of the same samples from 128 western gray squirrels
used in the Microsatellite DNA analyses were used for an additional
mitochondrial control region sequence analyses. Mitochondria are
structures in the cell, but outside of the nucleus, which contain DNA
inherited only from the mother. A 367 basepair portion of the DNA from
the control region of mitochondria was sequenced (Warheit 2003).
? The haplotype is the set, made up of one allele of each
gene. Haplotypes comprise the genotype (or genetic constitution of an
individual or taxon). They identified only three haplotypes from 40
Washington individuals, compared with 14 haplotypes from 27 Oregon and
California individuals, and no haplotype was shared across the Columbia
River.
? Genetic differences between populations can also be
measured using nucleotide diversity (i.e., average sequence
difference). The nucleotide diversity between populations equated to
long time intervals since these the Washington and California or Oregon
populations diverged (roughly 12,000 to 126,000 years ago).
? Some haplotypes in Washington are more closely related to
haplotypes in Oregon than other haplotypes in Washington.
Warheit (2003) summarized the results of these analyses by noting:
this study still requires additional analyses for at least three
reasons. First, samples sizes need to be increased for each of the
populations south of the Columbia River. Although I do not
anticipate that an increase in sample size for each of the Oregon
and California will significantly alter the conclusions drawn from
the current data set, a greater likelihood and confidence in these
conclusions will arise from more samples from Oregon and California.
Second, the overall levels of genetic diversity for each of the
seven microsatellite markers used in this study are low, and a
greater number of microsatellite loci will provide us with a broader
survey of the squirrel genome. [T]hird, we need to obtain the
control region sequences for the new samples included in the
expanded analysis of microsatellites. A more complete set of
analyses is needed on the control region data to help understand the
historical events that may have produced the phylogeographic
patterns drawn from the data (e.g., nested clade analysis).
Despite the preliminary nature of these analyses, the following
set of conclusions have been strengthened by the inclusion of a
larger sample size from the Fort Lewis and Okanogan Western Gray
Squirrel populations:
1. Washington populations of Western gray Squirrels show reduced
genetic diversity at both nuclear (microsatellite) and mitochondrial
(control region sequences) markers compared with populations from
Oregon and California. This reduction in genetic diversity may be
the result of genetic drift and relatively smaller effective
populations sizes.
2. There is significant genetic differentiation between
Washington Western Gray Squirrels, and squirrels from populations
south of the Columbia River. Both the microsatellite and sequence
data support the hypothesis that the Washington squirrels are a
population(s) distinct from those in Oregon and California.
3. There is significant genetic differentiation among the three
Washington populations. * * *
Additional and more variable microsatellites should be included
in any
[[Page 34639]]
subsequent study. It may be advantageous to develop microsatellites
specifically for Western Gray Squirrels, rather than adapt
microsatellites developed in other species of sciurids.
Thus, the preliminary information from Warheit (2003) suggests that
there is genetic differentiation between Washington western gray
squirrels, and squirrels from populations south of the Columbia River.
We believe that this information supports our contention that western
gray squirrel populations in Washington collectively or individually
could meet the discreteness criterion of the DPS policy. However, we
find that based on the genetic information currently available, the
western gray squirrel populations in Washington collectively or
individually do not differ markedly from other populations of the
subspecies in their genetic characteristics such that they should be
considered biologically or ecologically significant based simply on
genetic characteristics. Biological and ecological significance under
the DPS policy is always considered in light of Congressional guidance
(see Senate Report 151, 96th Congress, 1st Session) that the authority
to list DPS's be used ``* * * sparingly'' while encouraging the
conservation of genetic diversity.
One of the more notable pieces of genetic information in the
Washington populations is the lack of genetic diversity. As noted
above, this reduction in genetic diversity may be the result of genetic
drift and relatively smaller effective populations sizes. While there
is clearly some genetic information that shows that the Washington
populations are different from other populations (e.g., in the
microsatellite DNA analyses no haplotype was shared across the Columbia
River, also evidence suggests a long time interval since the Washington
and California or Oregon populations diverged), at this time we do not
be believe them to be markedly so. The information we believe
counterbalances the differential information is the fact that all
alleles present in each of the Washington populations are also present
in at least one of the Oregon or California populations, that some
haplotypes in Washington are more closely related to haplotypes in
Oregon than other haplotypes in Washington, and the fact that the
Washington populations of western gray squirrels show reduced genetic
diversity at both nuclear (microsatellite) and mitochondrial (control
region sequences) markers.
Information on genetics supports the contention that western gray
squirrels in Washington have been isolated from other populations for a
long period of time. The results suggest that genetic differences may
occur between populations of the western gray squirrel throughout its
range. The genetics studies by Warheit (2003) rely on relatively
limited sample sizes for some populations, n = 3 for California.
Results from the genetics studies may be confounded by the effects of
small population size and the consequent inbreeding and genetic drift.
The patterns of differentiation that were observed may reflect the
negative consequences of isolation, range contraction, and recent
significant declines of local populations. To what extent the forces of
isolation, genetic drift and/or inbreeding have impacted the western
gray squirrel population remaining in Washington is uncertain.
Conclusion
On the basis of available information, we determined that the
Washington populations of the western gray squirrel may be discrete in
relation to the remainder of the subspecies' populations. This
determination is based on information showing that the populations
appear to be geographically separated from, and to have some genetic
differences from, other populations to the south in Oregon, California,
and Nevada as a result of isolation by the Columbia River. But,
pursuant to our DPS policy, this apparent directness does not
necessarily mean that the populations in Washington are significant to
the remainder of the taxon.
Consequently, following a review of the available information, we
conclude that the western gray squirrel populations in Washington are
not significant to the remainder of the taxon. We made this
determination based on the best available information, which does not
demonstrate that (1) these populations persist in ecological settings
that are unique for the taxon; (2) the loss of these populations would
result in a significant gap in the range of the taxon; and (3) these
populations differ markedly from other populations of the subspecies in
their genetic characteristics, or in other considerations that might
demonstrate significance. Further, the available information does not
demonstrate that the life history and behavioral characteristics of
these populations in Washington are unique to the subspecies. We
acknowledge that, while the precise biological and ecological
importance of a discrete population segment is likely to vary from case
to case, we were unable to identify any other information that might
bear on the biological and ecological importance of these populations.
Significant Portion of the Range
Pursuant to the Act and our implementing regulations, a species may
warrant listing if it is threatened or endangered in a significant
portion of its range. Consequently, we evaluated the three populations
in Washington to determine if they collectively constitute a
significant portion of the range of the subspecies. In our evaluation
we considered whether the geographic extent of the range of the western
gray squirrel in Washington is significant relative to the remainder of
the subspecies' range. Based on the extent of the range of the western
gray squirrel subspecies, from southern California north to Washington
as discussed in the Background section of this notice, we do not
believe that Washington constitutes a significant portion of the
geographic extent of the subspecies, and subsequently the range of the
subspecies. Further, the available information regarding the collective
abundance of animals in the three populations in Washington does not
indicate that the Washington population constitutes a significant
portion of the western gray squirrel population rangewide.
Consequently, we have determined that the population of the western
gray squirrel in Washington does not constitute a significant portion
of the subspecies or its range.
Finding
We have carefully assessed the best scientific and commercial
information available regarding the discreteness and significance of
the western gray squirrel in Washington. We reviewed the petition,
literature cited in the petition, information available in our files,
peer-reviewed literature and other published and unpublished literature
and information, and information submitted to us during the comment
period following our 90-day petition finding. We have consulted with
biologists and researchers, including geneticists familiar with the
western gray squirrel, and reviewed the status of the western gray
squirrel in light of the requirements of our DPS policy. On the basis
of the best scientific and commercial information available, we
conclude that the populations of western gray squirrel in Washington do
not represent a DPS, and are therefore not a listable entity. Our
review did indicate that these populations may be discrete from other
western gray squirrel populations south of the Columbia River, but
under our DPS policy, the Washington populations collectively or
individually are not
[[Page 34640]]
significant to the remainder of the taxon. This finding is primarily
based on the fact that available information does not demonstrate that
the Washington populations have marked genetic, ecological, or
behavioral differences when compared with the remainder of the
subspecies. As such, we find that the petitioned action is not
warranted. Further, we have concluded that the three populations in
Washington are not significant to the remainder of the taxon, and
consequently do not constitute a significant portion of the range of
the subspecies.
References Cited
A complete list of all references cited in this document and
additional references can be requested from the Western Washington Fish
and Wildlife Office (see ADDRESSES section).
Author
This document was prepared by the Western Washington Fish and
Wildlife Office (see ADDRESSES section).
Authority
The authority for this action is the Endangered Species Act of
1973, as amended (16 U.S.C. 1531 et seq.).
Dated: May 30, 2003.
Marshall P. Jones, Jr.,
Acting Director, Fish and Wildlife Service.
[FR Doc. 03-14354 Filed 6-9-03; 8:45 am]
BILLING CODE 4310-55-P
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