Riparian brush rabbit (Photo:USFWS)

Jack Sparks, San Luis NWR and Craig Aubrey, Sacramento FWO

A secretive mammal that makes its home in the dense riparian woodlands of California’s San Joaquin Valley is currently the focus of attention at the San Joaquin River National Wildlife Refuge.  Through intensive habitat restoration and species reintroduction programs at the refuge, there is hope that the highly endangered riparian brush rabbit (Sylvilagus bachmani riparius) will one day flourish in its historic range.  Riparian brush rabbits are endemic to the Valley’s riparian woodlands, but 95 percent of this important habitat has been lost in California.  The last known wild population of the riparian brush rabbit was found in the 1990s along the Stanislaus River in San Joaquin County.  Since 2000, the refuge has worked with the Endangered Species Recovery Program at California State University, Stanislaus, U.S. Bureau of Reclamation, Sacramento Fish and Wildlife Office’s Recovery biologists, California Department of Fish and Game, and others to release and monitor captive-bred rabbits in the refuge’s well-suited dense riparian woodlands.  The ultimate measure of success will be to establish three new self-sustaining populations.

Seldom venturing out in the open, the rabbits depend on the heavy cover found in riparian woodlands.  Dense thickets of wild rose and blackberry, covered by canopies of oak and willow, provide protection from predators, such as raptors and coyotes.  Using funds acquired through a variety of sources such as the multi-agency collaborative CALFED Bay-Delta Program and Endangered Species Program Preventing Extinction funds, the refuge has been working with River Partners, Inc. – a non-governmental environmental organization –  to restore riparian habitat by planting over 250,000 native riparian plants on 1,000 acres (405 hectares) of refuge land.  Once mature, these plants will provide a safe haven for the rabbits and a vast assemblage of other native wildlife.  As riparian areas are prone to flooding, the planting design is determined by computer modeling that indicates how potential floodwater would move across the landscape, with flexible flood-tolerant plants placed in the direct path of water.  Large earthen mounds have been constructed to serve as high ground refugia for the rabbits to escape the rising water.  The re-introduced riparian brush rabbit population at the rRefuge is now the largest extant population in the wild, and the restored woodlands at the refuge the largest contiguous block of habitat in the rabbit’s range. 

In addition to activities conducted on lands owned by the Service, the refuge worked with the Sacramento Fish and Wildlife Office’s Recovery biologists to enter into a unique partnership with a private landowner to reintroduce the riparian brush rabbit to a private ranch.  The 2,048 acre (829 hectare) ranch is contiguous with lands being restored by the refuge, and includes some of the last available remaining privately owned riparian habitat available to help recover the rabbit.  Through the ongoing efforts of the Service and its partners, it is hoped that the riparian brush rabbit will one day be recovered.