Washington State Magazine

by Cherie Winner

What geology hath put asunder, biologists are joining back together.

This juvenile pygmy rabbit, cradled in colony manager Becky Elias's hands, is about two-thirds the size of an adult. Pygny rabbits are the smallest rabbits in North America, and they are the only rabbits that can thrive on a sagebrush diet. There's a hole in its ear where researchers removed a plug of tissue to use as a source of DNA, which helps the team trace family relationships in the colony. Photo by Shelly Hanks.

Lisa Shipley says she often gets calls from people who are convinced they have pygmy rabbits in their yard.

"I try to be really nice and not laugh," says the Washington State University wildlife biologist. She runs through a quick checklist with each caller: Do you have sagebrush in your yard? No. Do the bunnies have a fluffy white tail? Yes. Sorry, they're not pygmy rabbits.

Pygmy rabbits were last seen in the wild in Washington in 2001. Plagued by shrinking habitat, disease, and wildfire, populations that had been declining for years seemed to crash in the late 1990s. With extinction looming, federal and state wildlife officials decided to round up the remaining rabbits-all 18 of them-and begin a captive breeding program.

Some of the rabbits came to WSU, where Shipley and her colleagues Rod Sayler, Linda Hardesty, and Nina Woodford have been trying to produce enough healthy animals to release back into the wild. Other breeding colonies were set up at the Oregon Zoo in Portland and Northwest Trek near Eatonville, Washington.

Despite the rabbits' dire situation in the wild, Shipley says the recovery effort began with optimism.

"Rabbits, wow, they should be able to breed like crazy," she recalls thinking. But the animals weren't as amorous as expected. Bunnies of both sexes routinely fought and rarely mated. Facing a time crunch-pygmy rabbits live only four or five years, at most-the WSU team scrambled to figure out what would get them in the mood to mate.

Housing them in larger pens helped. In a big enough enclosure, one female and two males coexisted peacefully and produced multiple litters in one season. Another key factor was keeping them on soil. A mother-to-be needs to be able to dig a natal burrow where she will give birth, and where the kits will stay until they're weaned.

But keeping the rabbits on soil exacerbated another, potentially devastating problem: disease. During their first two years in captivity, the pygmy rabbits died at a frightening rate. Kits would be fine one day and dead the next, victims of an intestinal parasite. Adults succumbed to an infection caused by bacteria that live in the very soil the rabbits needed in order to breed.

Woodford, a veterinarian, says these bacteria usually pose a threat only to animals-or people-with severely compromised immune systems, such as patients in the late stages of AIDS. The pygmy rabbits' susceptibility hints that their immune systems might be deficient, perhaps because of inbreeding as their wild populations shrank.

Several factors contributed to their decline in the wild. Pygmy rabbits live among sagebrush growing on deep, soft soils throughout the inland Northwest. That would seem to be a vast enough area to support plenty of bunnies, but geology-the Columbia River and the patchiness of their deep soil habitat-has kept Columbia Basin pygmy rabbits separated from those in Oregon and Idaho for as long as 70,000 years. That isolation led to genetic differences that make the Washington rabbits unique, and worth saving as a distinct form of the species.

But isolation has also created problems. Populations in Washington, already separated from their kin in neighboring states, got cut off from each other as their habitat became more fragmented by agricultural development. Each population became more inbred and more vulnerable to disease outbreaks and predators.

In a last-ditch effort to save the Washington pygmies, the recovery team decided to bring Idaho pygmy rabbits into the breeding scheme. Sayler says such out-breeding, or "genetic rescue," was used several years ago to boost survival of the Florida panther by addition of a few panthers (or cougars) from Texas.

So far, the genetic rescue mission is working. Since bringing Idaho rabbits into the mix, dozens of kits have been born and raised to maturity. They've gone on to be mated with pure Washington rabbits to produce second- and third-generation bunnies that have 75 percent or 87.5 percent Washington genes-close to the original strain, but with a much greater chance of sustaining themselves in the wild.

"It looks like the intercrossed animals are going to save the day," says Sayler. With about a hundred mostly Washington pygmy rabbits now doing well in captivity, wildlife officials will decide this fall when and where to start releasing pygmy rabbits back into the wilds of central Washington.

Shipley says the breeding program calls for a different measure of success than that applied to most research projects.

"It's not one of those, 'I want to get a lot of publications out right away,'" she says. "It's bigger than that, and I think we should all feel pretty good about being part of it here at WSU."