Pygmy rabbit

The pygmy rabbit (''Brachylagus idahoensis'') is a rabbit species native to the United States. It is also the only native rabbit species in North America to dig its own burrow. The pygmy rabbit differs significantly from species within either the '' Lepus'' (hare) or '' Sylvilagus'' (cottontail) genera and is generally considered to be within the monotypic genus ''Brachylagus''. One isolated population, the Columbia Basin pygmy rabbit, is listed as an endangered species by the U.S. Federal government, though the International Union for Conservation of Nature lists the species as lower risk.

Description

The pygmy rabbit is the world's smallest leporid, with adults weighing between , and having a body length between ; females are slightly larger than males. The pygmy rabbit is distinguishable from other leporids by its small size, short ears, gray color, small hind legs, and lack of white fuzzy fur.

Distribution

The range of the pygmy rabbit includes most of the Great Basin and some of the adjacent intermountain areas of western North America. Pygmy rabbits are found in southwestern Montana from the extreme southwest corner near the Idaho border north to Dillon and Bannack in Beaverhead County. Distribution continues west to southern Idaho and southern Oregon and south to northern Utah, northern Nevada, and eastern California. Isolated populations occur in east-central Washington and Wyoming.

The elevational range of pygmy rabbits in Nevada extends from and in California from .

The last male purebred Columbia Basin pygmy rabbit, found only in the Columbia Basin of Washington state, died March 30, 2006, at the Oregon Zoo in Portland. The last purebred female died in 2008. A crossbreeding program conducted by the Oregon Zoo, Washington State University and Northwest Trek is attempting to preserve the genetic line by breeding surviving females with the Idaho pygmy rabbit.

Lifecycle

Pygmy rabbits are capable of breeding when they are about 1 year old.Wilde, Douglas B.; Keller, Barry L. (1978). An analysis of pygmy rabbit populations on the Idaho National Engineering Laboratory site. In: Markham, O. D., ed. Ecological studies on the Idaho National Engineering Laboratory site. 1978 Progress Report IDO-12087. Idaho Falls, ID: U.S. Department of Energy, Environmental Sciences Branch, Radiological and Environmental Sciences Lab: 305–316. .

The breeding season of pygmy rabbits is very short. In Idaho it lasts from March through May; in Utah, from February through March.Chapman, Joseph A.; Feldhamer, George A., eds. 1982. Wild mammals of North America. Baltimore, MD: The Johns Hopkins University Press The gestation period of pygmy rabbits is unknown. It is between 27 and 30 days in various species of cottontails (''Sylvilagus'' spp.). An average of six young are born per litter and a maximum of three litters are produced per year. In Idaho the third litter is generally produced in June. It is unlikely that litters are produced in the fall.

The growth rates of juveniles are dependent on the date of birth. Young from early litters grow larger due to a longer developmental period prior to their first winter.

The mortality of adults is highest in late winter and early spring. Green and Flinders reported a maximum estimated annual adult mortality of 88% in Idaho. Juvenile mortality was highest from birth to 5 weeks of age.

Pygmy rabbits may be active at any time of day; however, they are generally most active at dusk and dawn. They usually rest near or inside their burrows during midday.

Habitat

Pygmy rabbits are normally found in areas on deep soils with tall, dense sagebrush which they use for shelter and food.Flath, Dennis. 1994. Bunnies by the bunch. Montana Outdoors. 25(3): 8–13. Individual sagebrush plants in areas inhabited by pygmy rabbits are often 6 feet (1.8 m) or more in height. Extensive, well-used runways interlace the sage thickets and provide travel and escape routes. Dense
stands of big sagebrush along streams, roads, and fencerows provide dispersal corridors for pygmy rabbits.

The pygmy rabbit is the only leporid native to North America that digs burrows. Juveniles use burrows more than other age groups. Early reproductive activities of adults may be concentrated at burrows. When pygmy rabbits can utilize sagebrush cover, burrow use is decreased. Pygmy rabbits use burrows more in the winter for thermal cover than at other times of the year.

Burrows are usually located on slopes at the base of sagebrush plants, and face north to east. Tunnels widen below the surface, forming chambers, and extend to a maximum depth of about . Burrows typically have 4 or 5 entrances but may have as few as 2 or as many as 10. In Oregon, pygmy rabbits inhabited areas where soils were significantly deeper and looser than soils at adjacent sites. Site selection was probably related to ease of excavation of burrows. In areas where soil is shallow pygmy rabbits live in holes among volcanic rocks, in stone walls, around abandoned buildings, and in burrows made by badgers (''Taxidea taxus'') and marmots (''Marmota flaviventris'').

Some researchers have found that pygmy rabbits never venture farther than from their burrows. However, Bradfield observed pygmy rabbits range up to from their burrows.

Some areas inhabited by pygmy rabbits are covered with several feet of snow for up to 2 or more months during the winter. During periods when the snow has covered most of the sagebrush, pygmy rabbits tunnel beneath the snow to find food. Snow tunnels are approximately the same height and width as burrows. They are quite extensive and extend from one sagebrush to another. Above ground movement during the winter months is restricted to these tunnel systems.

Cover requirements

Pygmy rabbits are restricted to areas with heavy shrub cover.
Pygmy rabbits are seldom found in areas of sparse vegetative cover and seem to be reluctant to cross open space. In southeastern Idaho, woody cover and shrub height were significantly (P<0.01) greater on sites occupied by pygmy rabbits than on other sites in the same area.

Plant communities

Pygmy rabbits are found primarily in big sagebrush ('' Artemisia tridentata'') and rabbitbrush (''Chrysothamnus'' spp.) dominated communities.Severaid, Joye Harold. 1950. The pigmy rabbit (Sylvilagus idahoensis) in Mono County, California. Journal of Mammalogy. 31(1): 1–4. .Welch, Bruce L.; Wagstaff, Fred J.; Roberson, Jay A. 1991. Preference of wintering sage grouse for big sagebrush. Journal of Range Management. 44(5): 462–465. . Pygmy rabbits are also found in areas where greasewood (''Sarcobatus'' spp.) is abundant. Some woody species found on sites inhabited by pygmy rabbits in southeastern Idaho include big sagebrush, antelope bitterbrush ('' Purshia tridentata''), threetip sagebrush ('' A. tripartita''), low rabbitbrush ('' C. viscidiflorus''), gray horsebrush ('' Tetradymia canescens''), and prickly phlox ('' Leptodactylon pungens''). Grasses and forbs include thick spike wheatgrass ('' Elymus lanceolatus''), plains reedgrass ('' Calamagrostis montanensis''), sedges (''Carex'' spp.), prairie junegrass ('' Koeleria macrantha''), Sandberg bluegrass ('' Poa secunda''), bluegrass (''Poa'' spp.), needle-and-thread grass ('' Stipa comata''), western yarrow (''Achillea millefolium''), rosy pussytoes (''Antennaria microphylla''), milkvetch (''Astragalus'' spp.), arrowleaf balsamroot ('' Balsamorhiza sagittata''), buckwheat ('' Eriogonum'' spp.), tailcup lupine (''Lupinus caudatus''), and phlox ('' Phlox'' spp.). In the Upper Sonoran Desert pygmy rabbits occur in desert sagebrush associations dominated by big sagebrush and rabbitbrush with bitterbrush and sulphurflower ('' Eriogonum umbellatum var. stellatum'').

Food habits

The primary food of pygmy rabbits is big sagebrush, which may comprise up to 99% of the food eaten in the winter. Grasses and forbs are also eaten from mid- to late summer.Gates, Robert J.; Eng, Robert L. (1984) Sage grouse, pronghorn, and lagomorph use of a sagebrush-grassland burn site on the Idaho National Engineering Laboratory. In: Markham, O. Doyle, ed. Idaho National Engineering Laboratory radio ecology and ecology programs: 1983 progress reports. Idaho Falls, ID: U.S. Department of Energy, Radiological and Environmental Sciences Laboratory: 220–235 In Idaho, Gates and Eng found that shrubs contributed 85.2% (unweighted mean) of pygmy rabbit diets from July to December. Shrub use was lowest in August (73.1%) and highest in December (97.9%). Big sagebrush was the most important shrub in the July to December diet (54.2%), followed by
rubber rabbitbrush (''Chrysothamnus nauseosus'', 25.8%) and winterfat (''Krascheninnikovia lananta'', 4.6%). Grasses comprised 10% of the July to December diet and were consumed mostly during July and August. Indian ricegrass (''Oryzopsis hymenoides'') and needlegrass (''Stipa'' spp.) were the most important grasses consumed. Forbs contributed 4.9% of the July to December diet.

In southeastern Idaho, Green and Flinders found that pygmy rabbits ate big sagebrush throughout the year but in lesser amounts in summer (51% of diet) than in winter (99% of diet). Other shrubs in the area were consumed infrequently. Grass and forb consumption was relatively constant throughout the summer (39% and 10% of diet respectively) and decreased to a trace amount through fall and winter. Thickspike wheatgrass, bluebunch wheatgrass (''Pseudoroegneria spicata''), and Sandberg bluegrass were preferred foods in the summer.

Predators

Weasels (''Mustela'' and ''Neogale'' spp.) are the principal predators of pygmy rabbits. Coyotes (''Canis latrans''), red foxes (''Vulpes vulpes''), American badgers (''Taxidea taxus''), bobcats (''Lynx rufus''), great horned owls (''Bubo virginianus'') and northern harriers (''Circus hudsonius'') also prey on pygmy rabbits.Bradfield, Terry D. (1975). On the behavior and ecology of the pygmy rabbit. Pocatello, ID: Idaho State University. Thesis

Listing status

On September 26, 2007, Judge Edward Lodge of the United States District Court for the District of Idaho granted litigant party Western Watersheds Project summary judgment remanding the United States Fish and Wildlife Service 90-day finding denying conservationist parties' listing petition. The petition sought legal protection for pygmy rabbit as an endangered or threatened species.

References

External links

Washington Department of Fish and Wildlife, Pygmy Rabbit

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Leporidae
Rabbit, Pygmy
Rabbit, Pygmy
Mammals described in 1891
ESA endangered species
Taxa named by Clinton Hart Merriam
Endemic fauna of the United States