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Brachylagus idahoensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA LAGOMORPHA LEPORIDAE

Scientific Name: Brachylagus idahoensis
Species Authority: (Merriam, 1891)
Common Name/s:
English Pygmy Rabbit
Synonym/s:
Sylvilagus idahoensis (Merriam, 1891)
Taxonomic Notes: Brachylagus idahoensis is currently classified as a single species without subspecies designation across the range (Hall 1981). In the past, it was included in the genus Sylvilagus (Hoffmann and Smith 2005).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor/s: Beauvais, G.P., Sequin, E., Rachlow, J., Dixon, R., Bosworth, B., Kozlowski, A., Carey, C., Bartels, P., Obradovitch, M., Forbes, T. & Hays, D.
Reviewer/s: Smith, A.T. & Boyer, A.F. (Lagomorph Red List Authority)
Justification:
The population status of Brachylagus idahoensis is extremely varied across its discontinuous range, and its dependence on big sagebrush makes it particularly vulnerable to habitat loss from rangeland conversion and fire, and the resulting fragmentation often leads to decreased genetic diversity within populations (Dobler and Dixon 1990). Some populations, such as the extirpated Columbia Basin population, have declined drastically. However, there are several robust populations in less disturbed areas, and suitable habitat still exists in many areas.
History:
1994 Vulnerable (Groombridge 1994)

Geographic Range [top]

Range Description: General: B. idahoensis occurs throughout the Great Basin and neighbouring intermountain areas, in sagebrush habitat from southwestern Montana and western Wyoming in the east to southwestern Utah in the southeast and an isolated population in central Washington. The range also includes central Nevada to northeastern California, to the north in eastern Oregon and southern Idaho (Dobler and Dixon 1990). Within this wide range, it occurs in patches correlating positively to the density of sagebrush (Dobler and Dixon 1990).

Washington: B. idahoensis historically occurred in many areas of the Columbia Basin, but the sagebrush habitat has been heavily overgrazed and cleared completely for agriculture in many places. The population in Washington is now isolated from other populations (Dobler and Dixon 1990).

Idaho: Known populations of B. idahoensis are patchy but locally abundant in some areas within the valleys of the east-central region (Lemhi, Birch Creek, Big and Little Lost, and Pahsimeroi Valleys). Recently, isolated populations have been located in Owyhee County in the southwest of the state. Isolated populations also have been documented in the south-central region on the Camas Prairie (Rachlow 2004a).

An understanding of the current status and distribution of populations is limited by sampling effort; intensive surveys for populations have not been conducted in most areas. Within Idaho, agricultural and urban development of the Snake River Plains likely represents a significant barrier dividing populations north and south of the Snake River. Some populations north of the Snake River connect to those in southwestern Montana (including populations on the Continental Divide). South of the Snake River, populations likely connect to those in neighboring states (Oregon, Nevada, and Wyoming). The Idaho Conservation Data Center (IDCDC) has approximately 180 records of the species in the program's geospatial database, comprising both recent and historical records of occurrence. The World Conservation Union (IUCN) recommends that the area of occupancy be computed by overlaying the distribution of known occurrences with a uniform grid and tallying the area of occupied grid cells. Using a 2-km grid, we calculated the area of occupancy to be 748 km² using IDCDC records. Two important sites are the Idaho National Environmental and Engineering Laboratory (INEEL) and the Lemhi Valley, BLM lands south of Salmon, Idaho. Both areas have received significant research currently or in the past, and both support large populations of pygmy rabbits (Dixon and Bosworth 2004).

Wyoming: B. idahoensis in Wyoming appears to be widespread throughout the sagebrush-dominated portions of the Bear and Green River Basins. In the Bear River, B. idahoensis is consistently found in good numbers at Fossil Butte National Monument. In the Green River, B. idahoensis is consistently found to the south and west of the towns of Pinedale and Boulder. B. idahoensis appears to be widespread in the western quarter of the Great Divide Basin as well. The Jack Morrow Hills are known to support several occurrences. There is a single occurrence in the Sweetwater River Basin, just across the divide from the Great Divide Basin, documented in 2003; this signals the need for more sampling in the Sweetwater to determine the actual distribution there. This is the only known occurrence of the species on the east side of the Continental Divide in Wyoming (Beauvais 2004).

Oregon: The range of B. idahoensis in Oregon has not been determined. Recent surveys have found rabbits in Lake, Harney, Malheur, and Deschutes counties. Known areas include Foster Flat, Warner Valley, and north of Sheldon National Wildlife Refuge (NWR) (Carey et al. 2004).

Utah: Occurrences of B. idahoensis in Utah listed in Oliver (2004) have been augmented since the document's printing. Initial survey efforts have focused on the determining of presence or absence, but systematic searches in suitable habitat over large geographic ranges have given us a measure of relative densities. The top three most populous areas include the Western Box Elder County, Northern Rich County, and the Piute/North-western Garfield County. Within these areas, B. idahoensis is considered relatively common. The most notable absence of rabbits occurs throughout the central portion of Utah's Great Basin, which was included in historical estimates of the rabbit's statewide range (Kozlowski 2004).

California: They occur in Mono County California and are abundant from the Bodie Hills to south of Mono Lake. No pygmy rabbits have been relocated to northern California but surveys are on going (Sequin 2004). A recent survey found B. idahoensis present throughout the southern portion of its historic range in California, but did not find active sites in Modoc and Lassen counties in northern California (Larrucea and Brussard 2008).

Nevada: B. idahoensis is found from the state border in the north to the northern end of Nye and Lincoln Counties in the south and from the state border in the east to Vya, Nevada in the west. The pygmy rabbit is still found in most of the higher intermountain regions in the Great Basin Desert of Nevada (Sequin 2004). A recent survey found B. idahoensis present throughout the entire extent of its historic range in Nevada (Larrucea and Brussard 2008).

Montana: They are known from the extreme southwest corner of Montana (Dillon south to Idaho border) (Hays 2004).
Countries:
Native:
United States (California, Idaho, Montana, Nevada, Oregon, Utah, Washington - Reintroduced, Wyoming)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Washington: The Columbia Basin population of B. idahoensis was extirpated as of 2004 (Sayler et al. 2007), and is federally listed as endangered. A captive population exists with 21 Columbia Basin specimens of B. idahoensis and 26 rabbits crossed and backcrossed with B. idahoensis from Idaho (Hays 2004). Specimens taken to establish founding population for reintroduction had low reproductivity and high disease susceptibility, probably as a result of inbreeding depression. Intercrossing with B. idahoensis from Idaho was successful in restoring genetic diversity and increasing reproductive levels (Sayler et al. 2007). In March 2007, 20 rabbits were released as part of a reintroduction program in Douglas County, Washington (Oregon Zoo 2007).

Wyoming: The Wyoming Natural Diversity Database (WYNDD; University of Wyoming) has on file 93 records of B. idahoensis observations documented in Wyoming. Very few populations have been studied enough to draw reliable conclusions as to size or trend. The population at Fossil Butte National Monument as been studied at various times in the past, and appears to be rather abundant and persistent. In general, field biologists with good knowledge of B. idahoensis habitat can find individuals with relative ease within the known range of the species in Wyoming. In 2003, WYNDD biologists surveyed two areas outside of known range in the state; B. idahoensis was documented at one of these sites (Sweetwater River watershed, described above). Appropriate habitat is rather abundant and contiguous in southwest Wyoming; cheatgrass has not impacted this area to any great degree (yet) (Beauvais 2004).

Nevada and California: Sizes of populations and abundances of B. idahoensis in an area vary. Certain populations in Nevada are composed of vast expanses of burrows. Other populations may include only one burrow system with only about two rabbits photographed at the site. However, we do not know how far these rabbits can disperse and so do not know what constitutes a single population. Once an area is found to contain B. idahoensis, they are often located throughout the valley in reasonable numbers. Fragmentation of populations is largely unknown since we do not know much about dispersal potential. I have photographed juvenile rabbits in areas with no burrows, a long way from any known burrow sites. These rabbits may potentially be able to travel farther than we think as long as cover is provided. Fragmentation is a serious issue when fires or agricultural fields remove cover from vast areas (Sequin 2004).

Oregon: In 2000, a survey was conducted at 17 historical sites active in 1995 in southeast Oregon and only three sites contained evidence of current use by B. idahoensis. A 2001-2002 survey of 38 historical sites found evidence of recent use at only one location. However, recent surveys at new sites with habitat attributes preferred by B. idahoensis found evidence of rabbit use. On the Burns BLM district, 54 sites were surveyed and 12 sites showed signs of occupied rabbit use and undetermined use at 8 sites (Carey et al. 2004).

Utah: The more surveys that are conducted, the more rabbits are found. Populations of B. idahoensis in the Wyoming Basin, Great Basin, Colorado Basin, and Wasatch Mountains all appear to sustain habitat with robust numbers. It should be noted that to date, little to no attention has been paid to analyzing the density, genetic isolation, or trends of these populations (although surveys to increase our knowledge of these three issues are currently underway). It appears that the habitat that has remained intact since the last statewide examination of B. idahoensis in the 1940s also continues to maintain populations. Although it is clear that significant populations of B. idahoensis (both in terms of area and numbers) still inhabit Utah, overall loss of habitat has occurred since the 1950s, rendering large portions of their historical range unsuitable (Eastern Box Elder County, Central Great Basin, Southwestern Utah) (Kozlowski 2004).

Montana: Rauscher (1997) includes Horse Prairie, Big Sheep Creek, Sage Creek, Centennial Valley, the Sweetwater Basin, The Blacktail Wildlife Management Area, Antelope Flats, and the White Rocks as B. idahoensis range.

Idaho: In Idaho, known populations of B. idahoensis are highly fragmented, with the exception of the east-central valley region (Rachlow 2004b).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: General: B. idahoensis mainly occupies big sagebrush (Artemisia tridentata), especially where the vegetation is very dense. It forms burrows in soft, deep soils, in areas such as alluvial fans, often burrowing into a slope or rise in land elevation (Dobler and Dixon 1990).

As observed in captivity, free-ranging females construct natal burrows that are separate from residential burrow systems. The natal burrows have a single entrance leading to a nest chamber. Entrances to natal burrows are backfilled with soil and often are located at the base of shrubs (Rachlow et al. in prep). Preliminary observations based on radio-telemetry in the Lemhi Valley, Idaho, suggest that B. idahoensis moves longer distances than previously documented (more than 7 km for adults, and more than 6 km for juvenile rabbits) (Rachlow et al. in prep).

B. idahoensis is preyed upon by coyotes (Canis latrans), badgers (Taxidea taxus), weasels (Mustela frenata), bobcats (Lynx rufus), great horned owls (Bubo virginianus), long-eared owls (Asio otus), northern harriers (Circus cyaneus) (Dobler and Dixon 1990) and red foxes (Vulpes vulpes) (Green and Flinders 1980).

Wyoming: In Wyoming, B. idahoensis appears to follow the general accepted patterns of habitat use: an affinity for tall and dense sagebrush growing on friable soils. A few documented observations are from areas with only short and sparse sagebrush; there is some speculation (and only speculation) that B. idahoensis can occupy this type of habitat when wind is persistent enough to keep even short sagebrush exposed in the winter (i.e. the true habitat requirement is sagebrush exposed in winter, which in most areas is tall sagebrush, but in a few windy sites may be otherwise). Alternatively, these observations may represent juveniles dispersing through non-typical environments. In landscapes where short and sparse sagebrush is the matrix surrounding island patches of tall and dense sagebrush, B. idahoensis can be reliably found in the islands. Several field workers in south-west Wyoming have independently remarked that B. idahoensis tends to be most frequently found in an elevation band from approximately 6,500-7,500 ft (Beauvais 2004).

Nevada: B. idahoensis in Nevada seems to have similar habitat preferences as rabbits found in other states. They require loamy soils with big sagebrush. They can be located throughout entire valleys, but when not, they generally tend to be found in the largest, most dense clumps of sagebrush on appropriate soils. They have been located in areas with practically no understory (example: Reese Valley) as well as in areas with a heavy understory of forbs and bunch grasses (Sheldon Preserve). There may be competition between B. idahoensis and cottontail rabbits. Areas with high understory often have both rabbit types while areas with moderate understory only have cottontails. These cottontails have been found to be living in burrows that may have originally been made by B. idahoensis. In areas with practically no understory, B. idahoensis has been found with no cottontails (Sequin 2004).

California: B. idahoensis in California has similar habitat requirements to those in Nevada. However, the rabbits around Mono Lake are found in soils that have a higher sand content than populations found in Nevada. They are often found in "loamier" inclusions in stabilized sand dunes. Also, the rabbits in the Bodie area live at very high elevations (8,400+ ft). These rabbits are found in loamy soils in relatively low sagebrush (about 2-3 ft). They are still more likely to be found in the largest and densest sagebrush in the area (Sequin 2004).

Utah: Habitat use by B. idahoensis as inferred from burrow placement and distribution of pellets indicates preferential use of the densest patches of sagebrush available on the landscape. Use of sagebrush species (Artemisia tridentata tridentata, A. t.vaseyana, A. t. wyomingensis, and Artemisia arbuscula) and heights (30 -160 cm) varies considerably with elevation and latitude. It should also be noted that numerous sites considered by range specialists to be "overgrazed" (maintains its sagebrush over story, but exhibits substantial loss of grass and forb understory) contained large numbers of B. idahoensis. This, combined with their use of roadsides and disturbed edge, indicated that rabbits in Utah seem relatively flexible in their use of habitat, given sagebrush maintains proper canopy cover. Extensive snow tracking has been conducted in populations of the Wyoming Basin (Rich County). Initial analysis of non-dispersal movements indicated regular movements of 0.5-1.0 km within the first six hours after a fresh snowfall (Kozlowski 2004).
Systems: Terrestrial

Threats [top]

Major Threat(s): General: B. idahoensis is dependent on big sagebrush (Artemisia tridentata), it is particularly sensitive to habitat loss. Fires that are more frequent due to the increase of invasive cheatgrass, conversion to cropland and rangeland are contributors to loss of sagebrush habitat. Isolation of populations due to fragmentation of suitable habitat cause bottlenecks that threaten subpopulations. Dispersal is limited in fragmented populations, because B. idahoensis will not cross large open areas (Dobler and Dixon 1990).

Washington: In Washington, B. idahoensis is threatened by loss of deep soil shrub-steppe habitat, increase in fire frequencies due to cheatgrass invasion. Fires have the potential to remove sagebrush from vast areas. A recent fire in Washington State burned 66,000 hectares just outside the historic range of B. idahoensis. There are 417,000 hectares within the historic range of B. idahoensis in Washington with soil types where rabbits have been located. Of that amount, 27,000 acres remain in shrub-steppe today, and much of that has been degraded through fire and agricultural practices. Change in abundance and foraging of native predators due to habitat change are potential threats range wide that are largely unstudied (Hays 2004).

Wyoming: Although cheatgrass is not yet a major problem in southwest Wyoming, it is thought to be only a matter of time before it begins to dominate here as it has in states to the west. Also petroleum exploration and development is expected to increase markedly here, with consequent increase in sagebrush removal, alteration of fire cycles, increased road density, and increased potential for cheatgrass and other noxious weed establishment. Habitat managers appear to support more prescribed burning of tall and dense sagebrush, primarily to increase forage for big game and improve habitat for sage grouse. There is only occasional attention being paid to how this might harm B. idahoensis, as well as other vertebrates with similar habitat affinities (e.g. sage thrashers, sage sparrows). Heavy livestock grazing has the potential to reduce habitat quality for B. idahoensis, but it is important to recognize that southwest Wyoming was historically grazed by bison and white-tailed prairie dogs (Cynomys leucurus) with the latter species persisting into the present. Grazing by domestic sheep, cattle, horses, and feral horses occurs today, but was probably more intense and pervasive in the early 20th century and B. idahoensis are presumed to have persisted through that period. Disturbance of habitat in the vicinity of Bear Lake (ID) may reduce the already tentative connectivity between Wyoming populations and those to the west (Beauvais 2004).

Nevada and California: The main threat to B. idahoensis in Nevada and California is fragmentation due to vast fires. (These fires have extirpated populations from entire valleys and without leaving any cover behind may not allow rabbits to repopulate the area.) This is a severe problem that will most likely become greater with increasing cheatgrass invasion across Nevada. Agricultural fields are also a threat. Not only are they usually placed on the same loamy soils the rabbits prefer, but they also create a potentially impassable barrier and may increase the habitat suitability for cottontails. Road systems may also be a larger barrier to dispersal that we may think. In nighttimes road transect surveys in areas with known ratios of jackrabbits/cottontails/ B. idahoensis, B. idahoensis was consistently significantly underrepresented. This may be due to their reluctance to cross open areas (Sequin 2004).

Oregon: Threats to B. idahoensis in Oregon include fire (natural and managed), flooding, conversion to agriculture, exotic plants, decadence and overgrazing. The accumulative effects of the threats have contributed to habitat fragmentation and the isolation of populations (Carey et al. 2004).

Utah: The primary threat to B. idahoensis at this time is habitat loss. Loss occurs as a result of human development (historic losses: Wasatch Front north of Salt Lake; current losses: southwestern portion of the state in the vicinity of Cedar City), conversion to cultivated agriculture (northwestern portion of the Great Basin), degradation of plant communities due to overgrazing (widespread), increased fire frequency due to invasive weed understory (Great Basin), and large scale range improvement projects favouring the creation of large openings in mature sagebrush (Wyoming Basin, Lower Wasatch Range). As populations get smaller and more isolated, predators and disease may play more prominent roles as threats (Kozlowski 2004).

Idaho: B. idahoensis is threatened in Idaho by loss and/or modification of habitat including agricultural and urban development, invasive weeds, and changes in fire frequencies (Rachlow 2004b).

Montana: Rauscher (1997) mentions fragmentation of B. idahoensis habitat resulting from projects to improve rangeland for cattle as a threat (sagebrush is removed). He qualified that by stating that the rabbit is somewhat resilient and has the ability to use sites that were previously disturbed.

Conservation Actions [top]

Conservation Actions: General: Greater sage-grouse range overlaps with B. idahoensis range. Conservation of sage-grouse is a big issue and a federal listing may occur. Conservation of sage-grouse will likely benefit B. idahoensis to a significant degree. However, fire is being used to restore shrub-steppe and sage-grouse range in places, and although agencies are starting to include B. idahoensis in planning, it does not always happen (Hays 2004).

Washington: B. idahoensis from the Columbia Basin are federally listed as endangered. A recovery plan is being prepared, a captive breeding program is in place, habitat acquisition is proceeding, habitat management has changed, surveys have proceeded, reintroduction sites have been selected, and reintroduction techniques have been developed (Hays 2004). The reintroduction plan involves intercross breeding of B. idahoensis from the Columbia Basin with intraspecific rabbits from Idaho because of the bottleneck of genetic diversity caused by an extremely small population size (Sayler et al. 2007). The plan outlines reintroductions in 2007, followed by monitoring through the year for survival, dispersal, and reproductive success, and then a second reintroduction in early 2008 to augment the established population (Sayler et al. 2007). In March 2007, the first reintroduction of 20 rabbits bred by the Oregon Zoo were released in Douglas county, Washington, eight of which will be tracked by radio collar (Oregon Zoo 2007).

Wyoming: In Wyoming, B. idahoensis occurs on Fossil Butte National Monument; small population segments may extend onto Seedskadee and Bear River Meadows National Wildlife Refuges. These are all rather small and isolated protected areas. The vast majority of B. idahoensis populations in Wyoming occur on surfaces managed for multiple uses by the USDI Bureau of Land Management (BLM). A lesser amount of state and private land within the BLM matrix also supports rabbits. The USDA Forest Service may manage some small population segments at the high-elevation periphery of the species distribution. B. idahoensis is on the Sensitive Species list of the Wyoming State Office of the BLM, which requires that agency to consider the effects of management actions on B. idahoensis (Beauvais 2004).

Nevada: There is increased awareness but otherwise no conservation actions for B. idahoensis in Nevada. B. idahoensis populations are located in the Sheldon National Wildlife Refuge, as well as in the Great Basin National Park (Sequin 2004).

California: B. idahoensis is located at Mono Lake and Bodie State Historic Park and receive protection in these areas (Sequin 2004).

Oregon: Surveys are being conducted throughout the historic range of B. idahoensis in Oregon and additional surveys are planned for fall 2004 and 2005. A Master's student is studying habitat at Sheldon NWR. Also, a small telemetry project is underway. The BLM and Hart Mountain National Wildlife Refuge are now surveying for B. idahoensis prior to management activities such as road work and controlled burns (Carey et al. 2004). The Oregon Zoo has provided a source population for reintroductions of B. idahoensis in the Columbia Basin, Washington (Oregon Zoo 2007).

Utah: B. idahoensis is listed in Utah as a Species of Special Concern, and has been the focus of three ambitious grants designed to assess the effects of current land treatment practices on B. idahoensis, to examine historical trends in habitat loss, and to develop a statewide habitat model to increase management efficiency of the species (Kozlowski 2004).

Idaho: Current actions include increased survey efforts to document the occurrence of B. idahoensis within its range, and research into its ecology and habitat requirements. Captive breeding has been established for the Columbian Basin DPS and experimental reintroductions have been initiated for the species. Loss and/or modification of habitat include agricultural and urban development, invasive weeds, and changes in fire frequencies (Rachlow 2004). In 2004, 42 captive-bred rabbits were released into the wild at the Idaho National Laboratory for a study intended to evaluate techniques to be used for future Columbia Basin, Washington population reintroductions. Less than half survived more than 18 days, but survival may have been more successful if release pens were more protected from predators and if the rabbits had been released farther apart (Sayler et al. 2007).

Montana: B. idahoensis is listed as a species of special concern by Montana Natural Heritage Program (Rauscher 1997).
Citation: Beauvais, G.P., Sequin, E., Rachlow, J., Dixon, R., Bosworth, B., Kozlowski, A., Carey, C., Bartels, P., Obradovitch, M., Forbes, T. & Hays, D. 2008. Brachylagus idahoensis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 19 April 2014.
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