WHAT: San Joaquin River National Wildlife Refuge
WHERE: Entrance is at 2714 Dairy Road in Vernalis
DETAILS: In addition to housing the riparian brush rabbit and a variety of birds, the refuge has hiking trails and picnic areas for the public.
VERNALIS — It’s hard enough trying to track down an endangered species, but the reclusive nature of the riparian brush rabbit can make things particularly challenging for researchers.
Still, a team from the Endangered Species Recovery Program at California State University, Stanislaus, has been diligent tracking the small cottontail that is native to forested areas along the San Joaquin River and Stanislaus River.
“Even when they’re right in front of you, it’s hard to see them, because they’re right in the brush,” said Patrick Kelly, director of the program. “They’re secretive. As soon as they see you, they feel vulnerable.”
With the help of corncobs rolled in molasses and applesauce, biologists were able to lure and track 10 of the scarce rabbits during the past two weeks at the San Joaquin River National Wildlife Refuge about 20 miles north of Patterson.
The work, which started Oct. 29 and finished Nov. 8, was part of a twice-yearly census run by the ESRP to keep tabs on the general activity of the endangered species.
Kelly said the rabbit is important because it is an “umbrella species” — one that is equally or more sensitive to habitat changes than other species that live in the same area. Scientists have concluded that if riparian brush rabbit’s habitat needs are supplied, the needs of other species are being met, too.
“All of this should be viewed as an ecosystem restoration,” Kelly said. “It’s the restoration of a habitat type that has diminished drastically, really since the Gold Rush.”
While the study cannot definitively say how many of the rabbits exist in the refuge, it gives biologists a year-to-year comparison, explained Tristan Edgarian, a wildlife biologist with the ESRP.
A species on the edge
Biologists found seven rabbits in the spring and nine rabbits during a fall 2011 survey, Edgarian said.
The rabbit population was nearly wiped out by flooding in 2006, shortly after the animals were reintroduced to the wildlife refuge, he said. However, they fared much better when flooding occurred in the refuge in 2011, in large part due to restoration of native plants and the addition of brush-covered mounds of soil that helps serve as a refuge, Edgarian said.
Compared with the larger desert cottontails that also occupy the refuge, brush rabbits are more hesitant to leave brush-covered areas for fear of predators. Edgarian added that they can be swept away by floodwaters or picked off by predators.
Since the 2006 floods, Chico-based nonprofit River Partners has created habitat to help the rabbit and other native species. The group’s contributions include vegetation-rich “bunny mounds” of earth topped with native plants.
Such efforts appear to be succeeding, Edgarian said. Based on the size of one rabbit he found Nov. 8, the biologist determined it was more than 1 year old — and therefore must have survived the 2011 floods.
“This showed that all the work that we’re doing with the mounds and the vegetation has worked,” Edgarian said.
In addition to being funded by the U.S. Fish and Wildlife Service and the U.S. Bureau of Reclamation, work to restore the riparian brush rabbit and its habitat has been supported by an $8 million grant from the state-federal CalFed program, which seeks to address Delta restoration and farm water needs. Restoration efforts also have been supplemented by $750,000 from the Central Valley Regional Water Quality Control Board.
Rabbits make a comeback
An estimated 110,000 individual riparian brush rabbits once inhabited that historical range, according to the ESRP website.
But the population dropped dramatically starting in the 1940s, when dams — constructed for irrigation and flood control — were built on the major rivers of the Central Valley, according to the ESRP.
About 90 percent of their habitat was eventually destroyed.
Biologists estimated in 1993 that perhaps as few as 312 of the rabbits existed, all in Caswell State Park near Ripon. Even that number dwindled following massive flooding throughout the Central Valley in 1997.
Biologists began breeding and reintroducing rabbits to the San Joaquin River National Wildlife Refuge and surrounding private lands in 2002 from another population discovered in 1998 along Paradise Cut, a Stockton-San Joaquin Delta slough that borders the Stewart Tract between Tracy and Lathrop. A small population also remains in Caswell State Park.
While it is impossible to know how many riparian brush rabbits exist these days, it is safe to say they are making a comeback, according to Kim Forrest, manager of the San Joaquin River National Wildlife Refuge.
“We’ve moved light-years away from the late 1990s, when we wondered if we should declare the riparian brush rabbit extinct,” Forrest said.
Other wildlife also benefits
The 7,500-acre San Joaquin River National Wildlife Refuge, about half of which contains suitable habitat for the riparian brush rabbit in forested areas near Highway 132, also provides homes for other protected species.
Those include the riparian woodrat, vernal pool fairy shrimp and the vernal pool tadpole shrimp. A rare songbird called the least Bell’s vireo has been sighted there multiple years, and the refuge is a known resting place for the formerly endangered Aleutian Canada goose.
On Nov. 8, biologists found various creatures in brush rabbit traps, including the black rat — a nonnative species that carried the fleas responsible for spreading the Black Death in 14th-century Europe and China — and a California vole, a rodent native to the area. These critters were released after biologists spotted them in the traps.
As biologists found brush rabbits, however, they scooped them into sacks and waved an electronic scanner over them to see if any had been injected with a microchip that serves to identify them.
If not, biologists used a syringe to inject a chip the size of a grain of rice under the skin, clipped the animal’s ears with a tiny sterile hole punch and collected some fur for genetic analysis. Each rabbit was also given an ear tag for additional identification.
Looking ahead, those who are involved in restoration efforts hope to get more precise figures about the numbers of brush rabbits that exist, said Bob Parris, deputy refuge manager of the San Joaquin River National Wildlife Refuge. Meanwhile, they are pleased with the progress made thus far.
“I think everyone agrees that it’s been a really successful endangered species program,” Parris said. “The rabbit is in a much better situation than it was 10 years ago.”
For information: esrp.csustan.edu
Contact Jonathan Partridge at 892-6187, ext. 26, or firstname.lastname@example.org.