Columbia Basin Pygmy Rabbit

By Shruti Piduri

Source: Wikimedia

What is it?

Pygmy rabbits (Brachylagus idahoensis) are the smallest member of the family Leporidae, which is comprised of hares and rabbits. Adult pygmy rabbits average a weight of 375 to 500 grams, and a length of 23.5 to 27.5 centimeters. In other words, pygmy rabbits weigh around a pound, and are less than a foot long. In addition to their small size, pygmy rabbits can be distinguished by their small ears and small tail. Pygmy rabbits have grey fur and white bellies, with brown chests and legs.

Notably, pygmy rabbits are the only rabbit species native to the US that dig their own burrows. They use their burrows as protective shelter from weather as well as concealment from predators. Female pygmy rabbits create special “natal” burrows to protect their young in the first two weeks of their lives. Female pygmy rabbits have a gestation period of about 3 and a half weeks, and have one to four litters per year, with around three kits per litter. Sagebrush is a staple in the pygmy rabbit’s diet, and in the winter they rely almost completely on it for both food and for cover. In the summer, pygmy rabbits have a diet of about half sagebrush and half grasses and flowering plants. The mortality rates of pygmy rabbits vary from year to year, but they have an adult mortality rate of up to 88%.

The Columbia Basin population of pygmy rabbits is a distinct population segment of pygmy rabbits. Genetic analysis has shown that the Columbia Basin population is genetically distinct from other pygmy rabbits in the area. Pygmy rabbits as a species are not considered to be endangered, and are listed under “least concern” on the IUCN Red List.

Geographic Distribution of the Columbia Basin
Pygmy Rabbit (Source: USFW Recovery Plan)

Where does it live?

Pygmy rabbits were historically found throughout the western and northwestern states of the United States. The Columbia Basin itself is located in the Pacific Northwest, stretching from northern Oregon through central Washington and up to British Columbia, Canada. The Columbia Basin population of the pygmy rabbit has existed for over 10,000 years as a distinct population from the other pygmy rabbit populations surrounding it. Analysis has shown that the population is genetically different from other pygmy rabbit populations in the area.

Pygmy rabbits were first found in central Idaho in the 1890s by a naturalist. In the early 1900s, they were thought to be rare in the Columbia Basin, and by mid-century, they were thought to be extirpated from the Columbia Basin. In the 1980s, biologists found 5 small subpopulations in a county in central Washington. After the five subpopulations were found, they, along with a subpopulation found in 1997, started to decline. By 2001, five of the six found subpopulations were extirpated.

How was it listed?

The pygmy rabbit was listed as threatened in 1990 and then relisted as endangered in 1993 by the state of Washington. The distinct population found in the Columbia Basin was first federally listed as endangered (under an emergency rule) in 2001, and was fully listed as endangered in 2003. The Washington Department of Fish and Wildlife released an initial recovery plan in 1995, with updated recovery plans released in 2001, 2003, and 2014.

Why are they endangered?

The Columbia Basin population of pygmy rabbits was listed due to a number of threats:

Habitat Fragmentation: One of the major threats to the pygmy rabbit’s survival is the continued destruction and fragmentation of their habitat. The sagebrush that pygmy rabbits rely on is routinely removed from the area by humans developing the land for both urban and rural purposes, and approximately 60% of the shrubland in the area has been converted. As a result, pygmy rabbits have less habitat on which they can survive.

Pygmy rabbits rely on sagebrush for food and cover.
(Source: Washington Dept. of Fish and Wildlife)

Overutilization for Recreational and Scientific Activities: The pygmy rabbit can be hard to distinguish from cottontail rabbits, which are often hunted. Hunters are also not denied access to areas where the Columbia Basin pygmy rabbit lives. As a result, pygmy rabbits can sometimes be hunted accidentally. A small number of pygmy rabbits also die due to capture and recapture related reasons.

Disease and Predation: Although severe epidemics of disease have not been reported among pygmy rabbit subpopulations in the Columbia Basin, both plague and tularemia episodes have occurred within the population. Skeletal abnormalities also have been shown to occur in the population, and possibly developed due to inbreeding. Predation by many terrestrial and avian predators also hinders the population’s survival rate.

Other Factors: The population’s small size makes it more susceptible to being extirpated by random environmental changes or changes in food supply. The initial group of purebred Columbia Basin pygmy rabbits had low genetic diversity, adding to their high susceptibility to disease and the likelihood that characteristics such as skeletal abnormalities and a low reproductive rate would spread to the whole population.

Recovery Plan

The recovery plan for the Columbia Basin population of pygmy rabbits’ goal is to reclassify the population as “threatened” from “endangered” and ultimately to delist the population entirely. The plan lists seven actions that aim to increase the population’s survival rate: captive breeding, genetics, reintroduction, predator control, survey and monitoring, stakeholder involvement, and public awareness.

The Washington Department Fish and Wildlife’s captive breeding and reintroduction program was established in 2001. To begin, sixteen pygmy rabbits were captured from the wild and seven were sent to re-breeding facilities at the Oregon Zoo. In 2007, 20 rabbits from the captive breeding program were re-released into the wild, but the reintroduction failed due to high mortality rates, and none of the population lived to 2008. Captive breeding at the Oregon Zoo was discontinued in 2012, and the captively bred population was released into the wild and is faring much better than the 2007 population. Populations are released on sites owned and managed by the Washington Department of Fish and Wildlife.

The Washington Department of Fish and Wildlife also launched an intercross breeding program, attempting to increase the population by cross-breeding Columbia Basin pygmy rabbits with Idaho pygmy rabbits. Intercross breeding also increases genetic diversity within the population, which would reduce some of the adverse health effects caused by inbreeding. The intercross population has had higher reproductive rates, as well as better immunity to disease, than the purebred rabbit population.

Predator control, such as removing artificial food sources and perches for predators, was also undergone at sites occupied by pygmy rabbits. The Washington Department of Fish and Wildlife monitors pygmy rabbits in the wild through three intensive survey methods, and provides incentives to private landowners that take steps towards protecting the pygmy rabbit on their land. Finally, the Oregon Zoo and other partners take part in promoting public awareness of the pygmy rabbit’s situation.

What can you do? The Washington Department of Fish and Wildlife has worked to increase the survival of the Columbia Basin population of pygmy rabbits. By donating to it, you can support efforts to reintroduce pygmy rabbits into the wild and further their recovery. Clicking here will allow you to donate to a program run by the department that works to increase youth awareness of wildlife and endangered species, including the pygmy rabbit.

Works Cited:

U.S. Fish and Wildlife Service. Recovery Plan for the Columbia Basin Distinct Population Segment of the Pygmy Rabbit (Brachylagus idahoensis). 2012.

"Pygmy Rabbits." Western Watersheds Project. Western Watersheds Project, n.d. Web. 2 Dec. 2015.

Media Sources:

https://upload.wikimedia.org/wikipedia/commons/e/ed/BRACHYLAGUS_IDAHOENSIS.jpg

http://ecos.fws.gov/docs/recovery_plan/Columbia%20Basin%20Pygmy%20Rabbit%20Final%20RP.pdf (page 16)

http://wdfw.wa.gov/conservation/pygmy_rabbit/graphics/t_rabbit-20feeding-20on-20sagebrush.jpg https://www.youtube.com/watch?v=XROpZoxvCxU
https://uwintegratedsciences.files.wordpress.com/2013/12/washington-department-of-fish-and-wildlife-logo.jpg