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Pygmy Rabbit (Columbia Basin DPS)

Pygmy Rabbit

Scientific name:  Brachylagus idahoensis 

Status:  Endangered 

Listing Activity:  The Columbia Basin DPS of Pygmy Rabbit, Brachylagus idahoensis, was emergency listed as endangered in 2001, received final endangered status in 2003, a 5-year status review was completed in 2010, and a recovery plan was completed in 2012.   

  • Historical Status and Current Trends

    The pygmy rabbit’s historical range includes portions of Washington, Oregon, Idaho, Montana, Wyoming, California, Nevada, and Utah.  Based on fossil evidence and genetic analysis, the Columbia Basin pygmy rabbit in Washington became genetically isolated at least 10,000 years ago. The Columbia Basin pygmy rabbit represents an isolated portion of the northern-most extent of the species historic distribution.

    There is little information available regarding the historic distribution and abundance of pygmy rabbits in Washington.  Records indicate that during the first half of the 1900s, they probably occurred in Douglas, Grant, Lincoln, Adams, and Benton Counties.  Between 1987 and 1988, five small colonies of pygmy rabbits were found in southern Douglas County.  A sixth colony was discovered in 1997 in Grant County.  By 2001, the entire wild pygmy rabbit population in Washington was thought to consist of only one colony with fewer than 50 individuals.  The last known wild subpopulation of the Columbia Basin pygmy rabbit is believed to have been extirpated in 2004. 

    Habitat

    Pygmy rabbits are typically found in areas that include tall, dense stands of sagebrush (Artemisia spp.) which they are highly dependent on to provide both food and shelter throughout the year.  During the winter months their diet consists primarily of sagebrush, while in in the summer and spring their diets become more varied, with the addition of grasses, particularly native bunchgrasses to the sagebrush.  This species digs its own burrows, which are typically found in deep, loose soils.  However, pygmy rabbits occasionally do make use of burrows abandoned by other species, such as the yellow-bellied marmot.

    Life History

    The pygmy rabbit is the smallest member of the family Leporidae, which includes hares and rabbits.  Adults range between 9.3 and 11.6 inches in length and weigh less than a pound, making it the smallest rabbit in North America.  Fur color varies from brown to dark grey with white around the margins of their short, round ears.  They are distinguishable from other Leporids by their small size, short ears, small hind legs and lack of white on their tail.  They give alarm calls and other vocalizations, indicating some degree of sociality.   In addition, pygmy rabbits are the only North American rabbits that dig their own burrows and subsist almost entirely on sagebrush. 

    In Washington, breeding occurs from February through July.  Females may have up to three litters per year and average six young per litter.  Pregnant females dig secret, relatively shallow burrows, known as natal burrows.  Females begin to dig and supply nesting material to these burrows several days prior to giving birth, and may give birth and nurse their young in the runway to the burrow’s entrance. After nursing, the young return to the burrow and the female fills the burrow entrance with loose soil to disguise the immediate area and avoid detection.

    Pygmy rabbits are preyed upon by weasels, coyotes, badgers, bobcats, birds of prey, owls, foxes, and sometimes humans (pygmy rabbits are sometimes difficult for hunters to distinguish from other rabbit species).  Predation is the primary cause of mortality among both adults and juveniles and can be as high as 50 percent in the first five weeks of life.  Like other rabbits, pygmy rabbits mainly try to stay hidden and are cryptically colored to avoid predation. They are also capable of short bursts of speed in order to escape predators.

    Reasons for Decline

    Given the pygmy rabbits’ high dependence on sagebrush for food and shelter, large-scale loss and fragmentation of native shrub steppe habitat has played a primary role in the long-term decline of the Columbia Basin pygmy rabbit. However, it is unlikely that this was the only factor leading to the eventual extirpation of all known subpopulations. Once a population declines below a certain threshold, it is at risk of extirpation from a number of influences including chance environmental events (e.g., extreme weather), catastrophic habitat loss or resource failure (e.g., from wildfire or insect infestations), predation, disease, demographic limitations, loss of genetic diversity, and inbreeding. To varying degrees, all of these influences have impacted the Columbia Basin pygmy rabbit and, in combination, have led to the population’s endangered status.

    Conservation Measures

    A captive breeding program was implemented to retain, to the maximum extent possible, the different genetic characteristics of the purebred Columbia Basin population.  However, the wild Columbia Basin pygmy rabbits used to found the captive breeding population were likely suffering from severe inbreeding depression, and had a significantly diminished reproductive potential. They were not able to produce enough offspring for anticipated reintroduction efforts. It was decided that intercrossing the purebred captive animals with pygmy rabbits from outside of the Columbia Basin was necessary to try and conserve the population’s genetic characteristics.  No purebred Columbia Basin pygmy rabbit kits have been produced in the captive breeding program since 2005 and the last purebred Columbia Basin pygmy rabbit in captivity died on August 18, 2008. At this time it is unclear whether it is possible to conserve the remaining genetic characteristics of the purebred Columbia Basin animals.

    The USFWS and partners are working to reestablish a pygmy rabbit population in Washington. In 2011, the Columbia Basin pygmy rabbit breeding strategy was revised to increase the likelihood of successful population establishment.  Currently, there are 4 breeding enclosures and from fall 2011 through spring 2013, 109 pygmy rabbits were translocated from Nevada, Utah, Oregon, and Wyoming and placed in the large enclosures with the remaining captive-bred adults and kits.  Animals in the enclosures have produced over 2,000 kits since the 2011 breeding season, most of which have been released to the wild at the SFWA. Annual survival of the released animals varies, but has been as high as 30 percent and reproduction of fully wild animals has been documented. Monitoring of the wild pygmy rabbits at SFWA is ongoing and a second release site (Beezley Hills) has been identified. Additional release efforts are planned for these two sites in 2015. While estimation of dispersal, survival and current population numbers is difficult, analysis of fecal samples confirms that at least 91animals released in 2013 and 2014 remain in the wild at the SFWA, three of which were wild-born. We have successfully promoted semi-controlled breeding in these enclosures with pygmy rabbits from both the wild and captive-bred sources. 

     

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