Pygmy Rabbit Breeding and Reintroduction Project
David Shepherdson – Oregon Zoo, Portland, USA
The Columbia Basin pygmy rabbit (Brachylagus idahoensis) is the smallest rabbit in North America and one of only two that digs its own burrow. Together with sage grouse, pygmy rabbits are a key indicator of the health of the iconic intermountain west sage brush steppe habitat. Today, less than 50% of Washington's historic sage brush steppe remains. Pygmy rabbit numbers declined in Washington throughout the latter part of the 20th century due to habitat loss and fragmentation, primarily due to agricultural conversion. The isolated and distinct Columbia Basin population was listed as endangered by the State of Washington in 1993. In 2001, the US Fish and Wildlife Service (USFWS) listed the population as endangered under an emergency provision of the Endangered Species Act. Also in 2001, Oregon Zoo conducted the first-ever successful captive breeding of Idaho pygmy rabbits as surrogates for Columbia Basin pygmy rabbits.
Following this a decision was made by the Washington Department of Fish and Wildlife (WDFW) and USFWS to establish a captive breeding programme, with the goal of establishing a founding captive population for future recovery efforts. This action occurred in parallel with significant habitat purchase and restoration activities by WDFW. In May 2001, all 16 rabbits remaining at Sage Brush Flats, Ephrata, WA were captured and transported to breeding facilities at Oregon Zoo and the Washington State University. Prior to the 2004 breeding season, Northwest Trek Wildlife Park joined the breeding programme. Rearing and breeding these rabbits in captivity has proved challenging due to low genetic diversity and inbreeding in the founding population, which resulted in poor reproduction and high mortality. A decision was made early on by the USFWS pygmy rabbit recovery science team to increase genetic diversity and fitness by inter-crossing Columbia Basin pygmy rabbits with pygmy rabbits from other parts of the range.
After 10 years of ex situ breeding, a multi-year release programme began in 2011 and is currently underway. Wild-caught rabbits and ex situ bred rabbits are translocated to large breeding enclosures at the Sage Brush Flats reintroduction site to breed and the kits – 161 to date – are then released into the wild. WDFW and USFWS staffs are closely monitoring the released animals using radio-telemetry and faecal DNA monitoring. Zoo staff are assisting with construction of on-site breeding and release pens, translocation of wild rabbits and funding. After a hiatus of 10 years, Columbia Basin pygmy rabbits are once again living, breeding and digging burrows in the wild. Zoo staff has been contributing and lead authors on a number of scientific publications documenting reproductive physiology and behaviour, disease and the role of mate preference in reproductive success. In 2013, Oregon Zoo and Northwest Trek received the AZA North American Conservation Award for their role in this programme.