Wild News 1 Pygmy Rabbit

Researchers at Washington State University are working with federal and state wildlife biologists in a last-ditch attempt to save the Columbia Basin pygmy rabbit from extinction. The pygmy rabbit (Brachylagus idahoensis) is the smallest rabbit in North America, a foraging specialist that eats sagebrush, and one of only two North American rabbits that digs its own burrow. Despite its mild disposition, diminutive size, and weight of generally less than a pound, the Columbia Basin pygmy rabbit, that occurs only in Washington State, has been causing WSU wildlife researchers and veterinarians a lot of trouble in our efforts to prevent them from going extinct in the wild.

My WSU colleague, Dr. Lisa Shipley, and I no sooner began studying pygmy rabbit habitat for the Washington Department of Fish and Wildlife (WDFW) when our first graduate student on the project, Nikki Siegel, discovered there had just been a major population crash leaving perhaps less than 30 animals left alive in the wild in what had been the largest and possibly only remaining population in Washington State.

WDFW quickly assembled an advisory science team consisting of state, federal, and university biologists, zoo specialists, geneticists, and others to determine the best course of action to save the rabbits. The U.S. Fish and Wildlife Service, the lead federal agency for managing endangered species, listed the Columbia Basin pygmy rabbit as an endangered population segment under an emergency action in 2001, and then issued a final ruling to continue the endangered listing in March, 2003.

The WDFW science team determined that the best chance for saving the rabbits was to bring some of the few remaining animals into captivity to protect them and form a secure breeding population from which the animals could be reintroduced back into the wild when appropriate habitat was identified. WSU was selected to participate in both the captive breeding and reintroduction program, along with the Oregon Zoo and Northwest Trek, because of our excellent animal care facilities and available research and veterinary expertise.

Everyone is surprised to hear that pygmy rabbits do not necessarily "breed like rabbits" in captivity. Although they are indeed capable of having 2-3 litters of about 3-7 young, called kits, this theoretical productivity has seldom been achieved at WSU.

Unlike Idaho pygmy rabbits, which were used by the Oregon Zoo to develop the initial techniques for captive breeding, Columbia Basin pygmy rabbits brought into captivity did not reproduce well and seem to be particularly susceptible to diseases naturally harbored by the animal. Evidence now is accumulating rapidly that reduced genetic diversity in the small captive population is a contributing factor - a phenonmenon called inbreeding depression.

Idaho Reintroduction Program

One of WSU's contributions to the recovery effort for pygmy rabbits is to develop techniques to restore these animals back into appropriate habitat and document the behavior and survival of released rabbits. My graduate student, Robert Westra, is currently studying the success of reintroducing captive-bred Idaho pygmy rabbits back into extensive sagebrush habitat on the Idaho National Engineering and Environmental Laboratory (INEEL) in southeastern, Idaho.

We use Idaho pygmy rabbits as a surrogate for the Columbia Basin pygmy rabbit because these rabbits are not endangered in Idaho, which allows us to develop and test reintroduction techniques before they get applied on Washington rabbits.

We have received excellent support for the fieldwork on this pilot project from the Idaho Game and Fish Department and from wildlife biologists at the Stoller Corporation who conduct ecological monitoring on the INEEL and have assisted us with our field studies.

Reintroduction Techniques

We have released 27 radio-collared Idaho pygmy rabbits on the INEEL to date and have another last release of about 15-20 animals planned for the spring of 2004. Rob has monitored the released rabbits intensively for several months at a time and we have already obtained some encouraging results from this pilot study.

We release rabbits into an artificial burrow system constructed of plastic drainage tubing and dug into the soil to mimic a natural burrow and give them an initial home after release. We place a temporary wire holding cage over the two burrow openings to keep the animals in place while they adapt to the site and also to provide some initial protection from predators, such as hawks, coyotes, badgers, and weasels.

After a few days of being fed in place at the burrow site, we remove the containment cages and the animals are free to go wherever they wish. We have learned that rabbits will continue to use the artificial burrows after release, but many also disperse varying distances, began consuming natural forages immediately, and eventually dig their own burrows.

Even with this initial small sample, it appears that survival is higher when releases are made later in the year in fall, or possibly even late winter and early spring, when local predators are less abundant. This past spring, in 2003, we were pleasantly surprised to find that at least one of two surviving females from our release the previous fall had apparently had a litter of kits. Consequently, we are now optimistic that if enough Columbia Basin pygmy rabbits can be produced in captivity, we can devise an approach for reintroducing them back into carefully selected sites in Washington.

Recovery Efforts in Washington State

Ironically, the biggest hurdle we currently face in restoring the Columbia Basin pygmy rabbit in Washington is in producing enough young animals to support a strong reintroduction program. The founding captive population at WSU and elsewhere is not yet producing enough rabbits to build a large enough population to retain even the limited existing genetic diversity of the remaining Columbia Basin pygmy rabbits.

We continue to lose valuable genetic diversity of these captive rabbits because some genetically important animals occasionally die of old age or other causes, or may not mate and produce young with another individual that would help maximize overall genetic diversity of the captive population.

To solve these problems, there are probably at least 20 or more different biologists, veterinarians, geneticists, disease researchers, zoo specialists, and other scientists here and in other states helping on specific pieces of this problem. Different people are working to save DNA samples, solve disease problems, test for inbreeding depression effects such as lower immune functions and bone deformities, develop artificial insemination techniques, conduct nutritional studies, including those of Dr. Shipley's graduate student, Tara Davila, perform genetic analyses, and even possibly adapt cloning techniques originally developed for other kinds of rabbits.

Improving Genetic Diversity

The biggest management question we currently face is whether it will become necessary to mix some Idaho genes with those of the Columbia Basin population through crossbreeding, or genetic introgression, to alleviate some of the extremely harmful effects of inbreeding depression among the genetically-impoverished Washington rabbits. Dr. Shipley and I, as well as Dr. Linda Hardesty from WSU, are part of the U.S. Fish and Wildlife Service recovery team for the pygmy rabbit and this team has to make formal recommendations for population recovery to the federal government.

We are trying hard to avoid having to introduce genes from other population sources, but unless something happens quickly, it may be necessary to save the limited Washington pygmy rabbit gene pool and improve the survival and reproductive fitness of the remaining animals. This same type of genetic mixing was used to save the declining Florida panther by introducing a few cougars from Texas and it proved quite successful.