The Oregon Zoo is wrapping up a 12-year project to save the endangered Columbia Basin Pygmy rabbit.

The Zoo has released its last adult pygmy rabbits and their offspring in Eastern Washington’s Sagebrush Wildlife Area. And that marks the end of the Zoo’s program of breeding the endangered rabbit in captivity.

The pygmy rabbit, at less than a pound, is the smallest rabbit in North America. Photo courtesy of Oregon Zoo

The Columbia Basin Pygmy Rabbit weighs less than a pound, full- grown. Its population dwindled as it lost sagebrush habitat to agricultural development. The Oregon Zoo found that in 2001, just fifteen Columbia pygmy rabbits remained in the region.

The Zoo and its partner institutions have bred more than 1,600 rabbits in captivity since then. Leanne Klinski is the lead pygmy rabbit program assistant for the Oregon Zoo. She says the end of the program is bittersweet, but that the rabbits belong in the wild.

She explained, “To know that they are going to be out there and doing what they should be doing naturally is the only thing I could ask for.”

Courtesy Oregon Zoo

The rabbits won’t be entirely alone though. Klinski says that they will be kept in what are called soft release pens. Those allow the rabbits to roam, while protecting them from predators and making sure they have enough food to survive the transition.

This story originally appeared on Oregon Public Broadcasting.