Small Rabbit, Big Picture

Endangered Pygmy Rabbit's Plight Underscores Fragility Of Its Sagebrush Home

By Yasmeen Sands

Slate-gray, with tiny ears, a nondescript tail, and an average weight of less than a pound, the pygmy rabbit hardly seems like it would be a major fixture of any landscape. And, its modest appearance aside, it's not. As far as researchers like Rod Sayler can gather, the Columbia Basin pygmy rabbit, as Washington State's genetically distinct subspecies is known, is extinct in the wild.

"The only animals that exist now are a captive population of about 70 or so at Washington State University, Oregon Zoo, and Northwest Trek,” says Sayler, an associate professor in the Department of Natural Resource Sciences at Washington State University (WSU) in Pullman.

This captive population is the subspecies' last hope and the focus of an ongoing and, now, nearly decade-long research and captive breeding project aimed at reintroducing the rabbit back into Washington. The project culminated last March, when Sayler and his colleagues attempted the first reintroduction of captive-bred pygmies into the wild, an event reported in the January 2008 issue of National Geographic.

Despite the reintroduction's outcome--all of the released rabbits were preyed on by summer's end--researchers have not given up hope. Instead, they are going to great lengths to generate healthy populations of the rabbits and are using the plight of the pygmies as a backdrop for a bigger story: the need to protect sagebrush and shrub-steppe landscapes.

Found throughout the western states, pygmies are North America's smallest native rabbit. Their range is restricted to arid grasslands, known as shrub-steppe, that are replete with sagebrush, a coarse-leaved shrub that provides pygmies with food and shelter. The rabbits also require deep soils in which they can dig burrows to raise their young, known as "kits.”

Although populations of the pygmy rabbit have remained stable in other states, Washington's pygmies have not fared as well. As sagebrush habitats declined in eastern Washington over the past several decades, the Columbia Basin pygmy rabbit became increasingly isolated-—geographically and, ultimately, genetically, from populations in nearby states.

"In Washington, an estimated 75 percent of what was once sagebrush has been converted for agriculture,” says Steve Knick, a research ecologist with the U.S. Geological Survey (USGS) in Idaho who specializes in the study of shrub-steppe.

At the same time, the deep soils pygmies require for burrowing have been converted to wheat farming, ranching, and cattle grazing operations, and the landscape has become increasingly fragmented by roads.

As a result, pygmies became isolated into smaller and smaller pockets of habitat. In 2001, their shrinking population was afforded protected status, when the U.S. Fish and Wildlife Service recognized the Columbia Basin pygmy rabbit as an endangered species.

By the time formal research efforts began in the late 1990s, Sayler says, the subspecies was likely an extremely small population suffering from the effects of inbreeding.

Sayler and his colleague Lisa Shipley, also an associate professor in WSU's Department of Natural Resource Sciences, began studying the Columbia Basin pygmy rabbit in 1999. It was then that the Washington Department of Fish and Wildlife asked the researchers to study the effects of grazing on Sagebrush Flat, an area north of Ephrata, Wash., that was home to the last-known wild population of pygmies in the state. Near the end of their study, the researchers unexpectedly witnessed the rabbits' already fragile population crash. Sayler speculates that the cause of the crash could have been any number of factors, from disease to predation, interacting with the rabbits' small, genetically homogeneous population.

"We don't know exactly what tipped them over the edge,” he says. "At that point, everything was working against them.”

The choices, then, were either to bring in rabbits from other states or try to preserve the genetic diversity of Washington's rabbits, says Shipley. The state opted for the latter and called for a captive breeding program. Working under an emergency mandate, agency biologists captured all of the pygmies they could find in Sagebrush Flat, a total of 16 of them, and transferred the rabbits to captivity at WSU and Oregon Zoo.

"That's a tiny number to start captive breeding,” Shipley says. "We were really inbreeding from the minute we started.”

Problems with breeding pygmies in captivity quickly became apparent as the animals proved, contrary to conventional belief, that not all rabbits are easy breeders.

"When you're talking about a rabbit, people automatically assume they will be productive,” Sayler says.

Ironically, the first problem was getting female rabbits pregnant. Attributing the problem to the effects of inbreeding, the researchers introduced several pygmy rabbits from Idaho, a genetically separate, non-endangered subspecies, to the breeding program. The program's rabbits now carry a combination of Columbia Basin and Idaho genes.

Husbandry posed another challenge. Each breeding rabbit is housed in an eight-foot tank filled with 50 square feet of deep soil, much of which is trucked in from Clarkson, Wash., an area with soil similar to that of the rabbits' native habitat. To combat the constant threat of disease in the close quarters of captivity, researchers regularly disinfect each rabbit's soil supply and sweep it out daily. They also administer antibiotics to combat potentially lethal bacterial diseases.

Recently, the researchers installed larger, naturalistic breeding areas that are the size of two large carports and that can accommodate small groups of rabbits and greater volumes of soil. The WSU captive breeding facility, which Shipley manages, also maintains greenhouses where sagebrush, pygmies' chief food source, is grown year-round.

According to Shipley, three to four litters per rabbit each year are now common. But the newest challenge is keeping the kits alive to adulthood. Even in the best of conditions, it's uncommon for pygmies to live much more than a year.

"We are working on the problem of improving production in the captive population,” Sayler says. "After that, it will be how we get to reintroducing them to the wild.”

The researchers had their first opportunity to reintroduce captive-bred pygmies to the wild last March. Twenty rabbits fitted with radio-collars were released into artificial burrows in Sagebrush Flat and then remotely monitored over the following weeks. Most of the rabbits immediately dispersed from the burrows, which surprised the researchers, and the rabbits were quickly preyed upon. By late summer, all of them were gone.

"We learned a lot from that and realized what we're up against,” Sayler says. The priority now, he adds, is learning how to increase pygmy productivity. Greater numbers of rabbits will be needed for future reintroductions, he says, simply to compensate for the species' natural population dynamics and extreme vulnerability to predation.

"What's unique in our situation is that this is a relatively short-lived prey species,” Sayler says. "That makes it a real challenge to get this species back on the landscape again and makes it partly a numbers game.”

According to Shipley, the landscape is what the plight of the pygmy rabbit highlights. Greater attention needs to be paid to sagebrush and shrub-steppe, she says.

Knick, with the USGS, agrees. "Most people are just driving through sagebrush to get to another place,” he says. "But it's a very important component in the western United States.”

"We have to get people interested in shrub-steppe and start conservation way before we need captive breeding,” Shipley adds. "Pygmy rabbits are only one little piece of this whole problem.”

Yasmeen Sands is pursuing a Master's degree in technical communication at the University of Washington.

Images:

Top: Two of the first Columbia Basin pygmy rabbits bred at Washington State University's captive rearing facility rest at the entrance of an artificial burrow. The Columbia Basin subspecies is extinct in Washington's wild and now limited to three captive populations totaling about 70 animals. Photo: Tara Magee, Washington State University

Middle: Pygmy rabbits are the smallest native rabbit in North America, weighing less than a pound at maturity. Here, a newborn rabbit, known as a "kit,” is handled at Washington State University's captive breeding facility. Photo: Rod Sayler, Washington State University

Bottom: Sagebrush is a coarse-leaved shrub found in arid landscapes in the western U.S. Some 300 species depend on sagebrush for all or part of their lives, including the endangered Columbia Basin pygmy rabbit. Pictured is a sagebrush community in Idaho's Caribou National Forest.

Photo: James Henderson, Gulf South Research Corporation, Bugwood.org