|Scientific Name:||Spermophilus washingtoni|
|Species Authority:||(A.H. Howell, 1938)|
|Taxonomic Notes:||This species was included in Spermophilus townsendii until 1938.|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Yensen, E. & NatureServe (Hammerson, G. & Popper, K.P.)|
|Reviewer(s):||Amori, G., Koprowski, J. & Roth, L. (Small Nonvolant Mammal Red List Authority)|
Listed as Near Threatened because its range is not much greater than 20,000 km², its range is severely fragmented and there is ongoing fragmentation and loss of habitat. It does, however, occur in many protected areas, and the threats to habitats are starting to decrease hence the status of this species should hopefully stabilize. Almost qualifies as threatened under criterion B.
|Range Description:||The species' range includes the Columbia Plateau in eastern Washington east and south of the Columbia River, and northern Oregon between the John Day River and the Blue Mountains in the United States (Betts 1990, Verts and Carraway 1998). The three main occupied areas (two in Washington, one in Oregon) are highly disjunct, and separated by more than 50 kilometres (30 miles) of unoccupied land (Betts 1990). The elevational range is 90-450 m asl (Rickart and Yensen 1991).|
Native:United States (Oregon, Washington)
|Range Map:||Click here to open the map viewer and explore range.|
The total adult population size is unknown but likely exceeds 10,000. For example, 41 of the 80 colonies located by Betts (1990) were rated as small, 13 as moderate, and 26 as large. Assuming an average of 20 individuals in the small colonies, 60 for the moderate, and 150 for the large, total population size would be at least 6,280 individuals. This is purely an estimate based on average numbers, and it clearly underestimates the entire population as Betts (1990) did not completely survey all known habitat areas and many previously unknown colonies have been discovered since 1990.
In 2004, the Washington Department of Fish and Wildlife (WDFW) revisited 300 of roughly 500 known and historic detections in Douglas, Grant, and Adams counties. Surveyors found activity at approximately 240 (80 percent) of the sites. Probably some single colonies were represented by multiple detections, so the number of distinct occurrences is likely fewer than 240 in this area (USFWS 2004).
In Oregon (Boardman Bombing Range), only 115 of 188 (61.2 percent) colonies originally located in 1997, 2000, 2001, and 2002 were occupied in 2003 (Marr, 2003, unpublished data). TNC revisited all of the 90 known colonies (or 121 detections) on the Boardman Conservation Area in 2004. Sixty-six (73 percent) of sites were occupied in 2004. Of the 62 known in 1999, 44 (71 percent) were still occupied. Of the 20 sites first identified in 2001, 16 (80 percent) were occupied. While 24 sites had become vacant since 1999, 16 additional sites were located incidentally in 2004 (Marr 2004). Populations fluctuate with climate variations; populations may decline with drought, then recover with increased precipitation (and hence improved food resources) (Quade 1994, Greene 1999).
The range is now separated into three disjunct populations, although historically it was probably contiguous (Verts and Carraway 1998); the current range is estimated to be less than 50% of the historical range. The number of colonies has also dropped dramatically, and over 50% of those that have disappeared have gone since 1985 (USFWS 1999). Betts (1990, 1999) found that the species had disappeared from 73.8 percent of the sites in Washington and 76.9 percent of the sites in Oregon. Of the approximately 47 historic and new confirmed sites in southeastern Washington in 1987-1988, Washington ground squirrels were still evident at 37 (78 percent) in 1998 (Betts 1999). Sherman (2001) noted the loss of entire colonies of ground squirrels on the Columbia National Wildlife Refuge and Seep Lakes Management Area near Othello, Washington, despite the protected status of the species in the area.
|Habitat and Ecology:||
This ground squirrel occupies shrub-steppe habitat of the Columbia Basin ecosystem (USFWS 2004). It is most abundant in areas of high grass cover, on deep soils with low clay content (Betts 1990) and high silt content (Greene 1999). Young are born in a nest chamber in an underground burrow.
This species breeds late January-early February, soon after emergence from hibernation; later at higher elevations than at lower elevations. Gestation lasts probably 23-30 days. Young are born in February and early March. Litter size is 5-11 (average is eight). Young appear above ground in late March or April, nearly full-sized by late May (Rickart and Yensen 1991).
Klein et al. (2005) studied dispersal patterns of 125 radio-collared juvenile males in north-central Oregon. Mean dispersal probability was 0.718. Median dispersal distance was 880 metres (range up to 3.5 kilometres). There was suggestive evidence that survival of dispersers was higher than that of non dispersers.
Individuals live alone or in colonies. Badger probably is the most important predator. Diet includes herbaceous vegetation (including cultivated plants), roots, bulbs, seeds, and insects. Adults emerge from hibernation late January-March, feed throughout spring and into the summer, and accumulate much body fat. Adults are active until late May or early June, juveniles until late June or early July. During hot weather, most active in the morning (Rickart and Yensen 1991).
The range contraction and disappearance of colonies is primarily the result of loss and fragmentation of habitat due to conversion of native grassland and shrub-steppe to agricultural uses, such as wheat farms (Carlson et al. 1980, Betts 1990). In addition to removing required vegetative cover and forage, tilling and other soil disturbance destroys the necessary structure of the specific silty soil types (i.e., Warden soils) on which the species relies (Greene 1999). Intensive grazing removes vegetative cover and forage, degrading the habitat for ground squirrels (Greene 1999). Betts (1990) rated 21 of 80 colonies as highly vulnerable to extinction due to colony size, isolation from other colonies, land ownership, and threat from human activity.
However, the majority of existing colonies are located on the Boardman Bombing Range and the Boeing tract, which include the largest contiguous tract of suitable habitat (USFWS 2004). Although future Boardman Bombing Range activities are not certain, they are not expected to change significantly in the foreseeable future (USFWS 2004). In 2003, the largest threat to colonies in Oregon was the imminent conversion of the Boeing tract for agriculture. However, under a newly signed agreement, Threemile Canyon Farms placed 9,146 ha (22,600 acres) of the Boeing tract into a permanent ODFW Conservation Easement (Boardman Conservation Area), which is managed by TNC with the goal to maintain and improve where feasible the integrity of existing native communities and associated covered species (including the Washington ground squirrel) (USFWS 2004). All but two known sites and the majority of suitable habitat on the Boeing tract are located on the Boardman Conservation Area and therefore are protected from irreversible habitat modification (USFWS 2004). Hence threats from habitat loss have been significantly reduced in recent years. USFWS (2004) reasoned that this has reduced the immediacy of threats to the Washington ground squirrel, but actually it is the scope of threat that has been reduced; ground squirrel colonies that are not on conservation lands remain vulnerable to continued habitat loss (USFWS 2004).
Quade (1994) concluded that invasion of non-indigenous and noxious weeds also has contributed to the degradation of the habitat.
Ground squirrels are often viewed as pests and are subject to recreational shooting and poisoning to reduce impacts to agricultural crops (USFWS 2004). Olterman and Verts (1972) attributed the decline of Washington ground squirrels from 1948 to 1970 to years of control by poisoning and/or shooting, in addition to significant habitat loss.
Predation by badgers can be a significant mortality factor. Badger predation may cause local extirpations of small, isolated colonies (Betts 1999).
Sylvatic plague, which was responsible for large population declines of Spermophilus townsendii (a closely related species) several decades ago, is a potential threat (USFWS 2004).
United States Endangered Species Act: Candidate (12 Sep 2006). United States Fish and Wildlife Service Lead Region: R1 - Pacific
Roughly 64 percent of known Oregon sites are located on federal land (Boardman Bombing Range and Horn Butte), 35 percent are located on private land that is under an ODFW conservation easement, and the remaining one percent is located on other private lands (USFWS 2004).
The Boardman Bombing Range (northern Oregon), which supports the highest known concentration of Washington ground squirrels and best available habitat (Carlson et al. 1980, Betts 1990, Quade 1994, Greene 1999), is not fully secure. Research Natural Areas on the bombing range protect 2,046 hectares, but the remainder of the bombing range (8,024 hectares) is managed by the Navy for military training and grazing allotments (Quade 1994, Greene 1999) (grazing has not been allowed in recent years). Protected habitat is also located on a small preserve owned by The Nature Conservancy just south of the bombing range.
In Washington, most sites are located on the state-owned Seep Lakes Wildlife Management Area, the BLM's Wenatchee Resource Area, and the Columbia National Wildlife Refuge. The Badger Mountain sites (Betts 1990) were located on private land.
Continued inventories are needed. Conservation easements should be pursued on private lands.
|Citation:||Yensen, E. & NatureServe (Hammerson, G. & Popper, K.P.) 2008. Spermophilus washingtoni. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 01 September 2015.|
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