Magazine article National Parks

Counting Sheep

Magazine article National Parks

Counting Sheep

Article excerpt

Airlifting bighorn sheep back into the Sierra Nevada's national parks.

THIS MARCH, a LARGE helicopter thrummed over the 15,000-foot-high pinnacles of Yosemite National Paiks Cathedral Range with an aluminum box dangling from a long cable. Inside the box were sheep-four Sierra Nevada bighorns waiting (patiently, in fact) to touch down in their new home, a rocky slope nubbled with glacial scree and lodgepole pines. "That's the scariest part for me," said California Department of Fish and Wildlife biologist Tom Stephenson, whose eyes were locked on the transport helicopter from a second helicopter. "Watching that box hang, and making sure it gets there safely."

Biologists and the conservation community have been working for decades to restore populations of this endangered paragon of the Sierra Nevada's rugged wilderness. Translocations-the transfer of rams and ewes from healthy herds to vacant habitat-have been their chief strategy to reestablish herds that once prospered along the Sierra crest. The March Yosemite drop, and another a few days later in Sequoia National Park, were the most complex translocations conducted in the Sierras so far. They are also close to the last-the sheep, scientists predict, can mostly take it from here. Stephenson, who leads the recovery effort, said that the new managed herds are thriving. Within five years their numbers should support downlisting from endangered to threatened. Permanent delisting should follow.

"Over the decades, I've heard some pessimists say that we'll never delist Sierra Nevada bighorn sheep," said Kevin Hurley, conservation director of the Wild Sheep Foundation. "Well, we're getting closer all the time."

Historically, bighorn sheep were common in alpine areas from British Columbia to northern Mexico. There are three subspecies: Rocky Mountain bighorns along the Continental Divide, desert bighorns of the arid Southwest, and the most isolated subspecies, the Sierra Nevada bighorns. Two hundred years ago, as many as two million bighorn sheep lived in North America. But exploitation during westward expansion, as well as the installment of domestic sheep, which can host pathogens fatal to wild sheep, drastically reduced these numbers. By the 1950s, bighorn populations were patchy and thin-only 25,000 sheep remained.

Sierra Nevada bighorns were always the most vulnerable because they are the most geographically isolated subspecies with the smallest population. Genetically distinct from the other types, these sheep, with their unique wide-flaring horns, evolved to thrive in the Sierras' contiguous high-elevation crest, primarily on the drier eastern slopes. About 1,000 bighorn sheep occupied this mountain range before European settlement. By 1995, scientists could find only 100 Sierra Nevada bighorns in the whole range.

Thanks to a sustained conservation effort among state and federal agencies, hunters, tribal commissions, and other entities, bighorn populations across North America have more than tripled from their 1950s low. That's largely a result of the relocation of 21,000 sheep since 1922. While the practice didn't really pick up until the 1940s and '50s, on average, that's nearly 20 airlifted sheep a month, said Hurley.

The recovery stoiy for Sierra Nevada sheep is even more remarkable, with populations rebounding to six times their 1995 numbers. The range's national parks-Yosemite, Kings Canyon, and Sequoia-have been critical to this success because of their nearly intact habitat. But although sheep translocations have been occurring in the Sierras since the 1980s, the targeted sites have straddled only the parks' eastern fringes. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed


An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.