Riparian Brush Rabbit

Sylvilagus bachmani ssp.riparius

Description

The riparian brush rabbit is a medium to small cottontail 11.8-14.8 in (300-375 mm) in length and weighing 1.1-1.8 lb (500-800 g). The color varies from dark brown to gray, with a white underbelly, which is similar to the desert cottontail.

The riparian brush rabbit shares a similar habitat with the desert cottontail, but can be distinguished by a smaller, more inconspicuous tail and uniformly colored ears. Also unique to the riparian brush rabbit is the convex nasal/upper jaw region of the skull. Other subspecies of Sylvilagus bachmani are straight or concave.

Behavior

Brush rabbits need dense, brushy cover to hide. They do not like open spaces and linger for several seconds to minutes before leaving their cover, rarely venturing farther than 3 ft (0.9 m) from a dense thicket. If pursued, they immediately leap into the cover of shrubs. They will not cross large, open areas, which limits their dispersal beyond the brushy riparian forests.

Riparian brush rabbits are also known to climb bushes and trees awkwardly, which provides the ability to survive inundation by periodic flooding.

Breeding occurs January through May, with a litter size anywhere from two to five. Young are born helpless, but reach maturity after a year.

Home ranges of males are larger than females, but do not overlap the females' primary activity center.

Habitat

Riparian forests with a dense understory shrub layer are the riparian brush rabbit's primary habitat. If the forest canopy is closed, there is rarely adequate brush to support a riparian brush rabbit population. There must be small clearings for the rabbits to bask in the sun and feed on a variety of herbaceous vegetation.

Rabbits live in tunnels that run through vines and shrubs of low growing mats of California wild rose and Pacific blackberry. Associates include wild grape, Douglas' coyote bush, and grasses.

Distribution

Historically, riparian brush rabbit recordings and sightings were known along the San Joaquin River near the boundary of San Joaquin and Stanislaus Counties in California. There is belief that the habitat once extended along the Sacramento and San Joaquin river systems, from Stanislaus County to the Delta region, but the rabbit was not described until after it had already been extirpated from much of its original home range.

There is one population of the riparian brush rabbit subspecies located on a fragment of riparian forest on the Stanislaus River in Caswell Memorial State Park, in the San Joaquin County on 258 acres (104.5 hectares). Population size has reached as high as 608 individuals in 1993, but after flooding in 1997 populations were reduced severely. Only one rabbit was live trapped in 1998.

Threats

There has been a nearly 90% reduction of historical riparian communities throughout the riparian forests along major streams flowing onto the floor of the northern San Joaquin Valley due to urban, commercial, and agricultural development, wood cutting, reclamation and flood control activities, groundwater pumping, river channelization, dam construction, and water diversions.

Flooding, in combination with other activities, has severely impacted this already restricted population. The increase of habitat conversion to agriculture combined with construction of dams has altered the timing, frequency, duration, and intensity of flooding. Conversion to cultivation eliminates hedgerows and other patches of cover that provide travel corridors and refuge.

The rabbit's habitat is confined within levees offering little protection during routine winter flooding or no refuge during major flood events. When flooding occurs, foraging habitat and shelter are eliminated within the levees.

Due to habitat limitations, as well as small population size, the riparian brush rabbit is at risk of being further harmed by naturally occurring events such as wildfire, disease, predation, competition, and loss of genetic variability from inbreeding.

Hunting may also affect riparian brush rabbits if they disperse beyond boundaries of the park. Regulations set by California Fish and Game Commission do not distinguish between the riparian brush rabbit and other subspecies of S. bachmani that are currently hunted.

Conservation and Recovery

Steps are being taken to protect the riparian brush rabbit from harm through the Department of Parks. The California Department of Parks and Recreation has developed a riparian brush rabbit management plan for Caswell Memorial State Park.

In addition, San Joaquin County is developing a multispecies habitat conservation plan which considers habitat for the riparian brush rabbit. Some of the measures suggested under the plan may minimize negative impacts or benefit the rabbit.

A fire management plan has also been initiated for the Park to protect habitat, but fires from outside sources still pose a threat.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

Sacramento Fish and Wildlife Office
U. S. Fish and Wildlife Service
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619

Reference

United States Department of the Interior. 23 February 2000. "Endangered and Threatened Wildlife and Plants: Final Rule to List the Riparian Brush Rabbit and the Riparian, or San Joaquin Valley, Woodrat as Endangered." Federal Register 65 (36):8881-8890.