Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
PACIFIC SOUTHWEST REGION: Riparian Brush Rabbit Reintroduction and Rescue Efforts at the San Joaquin River National Wildlife Refuge
California-Nevada Offices , November 16, 2011
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Riparian brush rabbit in tree before being rescued.
Riparian brush rabbit in tree before being rescued. - Photo Credit: CSU Stanislaus, Endangered Species Recovery Program staff
Tristan Edgarian (ESRP) handing off a rescued riparian brush rabbit to Eric Hopson (USFWS).
Tristan Edgarian (ESRP) handing off a rescued riparian brush rabbit to Eric Hopson (USFWS). - Photo Credit: CSU Stanislaus, Endangered Species Recovery Program staff
Tristan Edgarian (ESRP) holding two rescued riparian brush rabbits.
Tristan Edgarian (ESRP) holding two rescued riparian brush rabbits. - Photo Credit: CSU Stanislaus, Endangered Species Recovery Program staff
A rescued riparian brush rabbit.
A rescued riparian brush rabbit. - Photo Credit: Eric Hopson, USFWS

By Caroline Prose, CVPIA Habitat Restoration Program

The San Joaquin River National Wildlife Refuge (NWR) is located in Stanislaus County, California. The refuge encompasses more than 6,500 acres of riparian woodlands, seasonal and permanent wetlands, and grassland habitats that are home to a diversity of wildlife native to the Central Valley. One of the species inhabiting riparian habitats at the refuge is the federally endangered riparian brush rabbit (RBR) (Sylvilagus bachmani riparius).

In March 2011, a series of winter storms produced significant amounts of above average rainfall which caused detrimental flood conditions along the San Joaquin and Stanislaus Rivers, threatening the RBR at the refuge. In response, Endangered Species Recovery Program (ESRP) and refuge staff undertook an arduous rescue effort to prevent the drowning of as many RBRs as possible. Boats were used to find and remove RBRs from trees in low areas, place them in gunnysacks and boxes, and ferry them to bunny mounds and other high ground. Over the course of several days, at least 125 RBRs were rescued and moved to higher ground.

Tristan Edgarian, Jeff Holt and Nick DeVorss from ESRP, and Eric Hopson, Matt Lloyd and Reyn Akiona from the Service worked long, strenuous, and exhausting hours to rescue these rabbits, under hazardous and difficult conditions. Others who assisted with the RBR rescue efforts included Patrick Kelly from ESRP, Kim Forrest, Tim Keldsen, Lee Eastman and Dennis Woolington from the Service, and Julie Rentner and Jessica Hammond from River Partners. These individuals’ outstanding efforts were recognized by giving each person involved with the rescue effort a “Certificate of Appreciation” on behalf of the Bureau of Reclamation’s (Reclamation) Central Valley Project Conservation Program (CVPCP) and Reclamation and the Fish and Wildlife Service’s (Service) Central Valley Project Improvement Act Habitat Restoration Program (CVPIA HRP). Their efforts should yield long-lasting benefits toward the eventual recovery of this endangered species.

Learn more about the riparian brush rabbit and the ESRP:

The RBR is a medium to small cottontail in the Leporidae family. Thirteen brush rabbit subspecies are distributed from the Columbia River in Oregon and Washington, to the tip of Baja California. RBRs can be distinguished from desert cottontails (Sylvilagus audubonii), with which they co-occur, by their smaller, inconspicuous tail and uniformly colored ears (i.e., no black tips). RBRs breed from around January to May, and the average litter size is three or four young.

Habitat for the RBR consists of riparian communities dominated by willow (Salix spp.) thickets, California wild rose (Rosa californica), Pacific blackberry (Rubus ursinus), California wild grape (Vitis californica), Douglas' coyote bush (Baccharis douglasii) and various grasses. RBR avoid large openings in shrub cover, and frequent small clearings, where they feed on a variety of herbaceous vegetation.

The RBR has been extirpated from most of its historic range. This federally- and state-listed species is known only from Caswell Memorial State Park, a 250-acre parcel on the Stanislaus River about 5 miles north of the San Joaquin NWR, the South Delta area near Lathrop, and a reintroduced population on the refuge and associated lands. On-going threats are habitat conversion to agriculture, wildfire, disease, predation, flooding, clearing of riparian vegetation, and the use of rodenticides. There has been about a 90 percent reduction of Central Valley riparian communities because of elimination and modification of riparian forests along valley floor river systems due to urban, commercial, and agricultural development, wood cutting, reclamation and flood control activities, heavy groundwater pumping, river channelization, dam building, and water diversion.

Since 2002, the California State University, Stanislaus, Endangered Species Recovery Program (ESRP), has successfully guided a captive breeding and translocation program for RBRs (RBR program), with financial support from the CVPCP, CVPIA HRP, Reclamation’s South-Central California Area Office, California Department of Fish and Game, CalFed Bay-Delta Program, private landowners, and others. Through the RBR program, captive-bred RBRs have been reintroduced, including to historic habitat on the refuge. ESRP is a cooperative research program developed for biodiversity conservation in central California.

Over the years, the RBR program has faced significant challenges, including the Pelican Fire, which swept through most of the San Joaquin River NWR in the summer of 2004; near catastrophic flooding which covered most of the refuge in spring and summer of 2006; and funding shortages in 2008 and 2009 due to the California budget crisis. Nonetheless, the 2006 flooding and resulting RBR fatalities led to the development of innovative habitat solutions whereby the refuge and River Partners, Inc., a non-profit organization committed to restoring riparian habitat for wildlife, collaborated to provide critical high water refugia for RBR. With financial support from the CVPIA HRP, the CVPCP, and others, River Partners was able to enhance habitat conditions for the RBR, especially with regard to the risk from flooding.

Elevated “bunny mounds” were constructed within riparian habitat areas throughout the refuge, and planted with protective cover to serve as flood refugia areas.On-going monitoring indicates that the RBR population at the refuge appears to be rebounding, and many of the RBRs are taking advantage of these bunny mounds. Construction of the mounds is part of a larger effort to restore high quality native riparian vegetation at the refuge and nearby private lands to fulfill a long-term need for diverse, native riparian habitats for RBR. This multi-faceted effort will enable the species to withstand future flooding events and achieve self-sustaining populations.

Please see the link below to a video on the RBR rescue effort, prepared by Maryann Owens of the Service’s Sacramento Fish and Wildlife Office, and narrated by Eric Hopson, Manager of the San Joaquin River NWR.


Contact Info: Caroline Prose, 916-414-6575, Caroline_Prose@fws.gov
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