Desert bighorns are native to arid regions of the West. These animals – slightly smaller than the high-country Rocky Mountain bighorns – are well-adapted to desert canyons.
Twenty years ago, the DOW established a new population of desert bighorn in the Upper Dolores Canyon area in San Miguel County, with a group of 50 sheep obtained from Nevada. Over time, the herd has grown to number about 150 animals.
In December 2010, sheep captured from this herd were relocated to an area north of the Big Gypsum Valley in Montrose County, about 15 miles away, to augment its small existing herd. If the relocated bighorns do well, biologists may relocate another 15 next year. Two other desert sheep herds exist in the state, in Colorado National Monument, west of Grand Junction, and in the Escalante/Dominguez Canyon area, west of Delta.
“The herd in the upper Dolores River area has been growing, but another herd in some good bighorn habitat just down the canyon isn't doing as well,” said Scott Wait, senior terrestrial biologist for the DOW's southwest region in Durango. “Having more animals in more places will improve the long-term outlook for the species. Giving the Middle Dolores herd a boost will help us do that.”
DOW biologists examined each of the transplanted sheep, which were rounded up on Dec. 16, to assess their health and to get blood samples. The sheep were then fitted with radio collars to allow biologists to monitor their movements and survival, and were released the next day.
This is the third time the DOW has attempted to establish desert bighorn in the Middle Dolores Canyon. Two other attempts, in 1990 and 2001, did not result in the establishment of a new herd. Biologists believe that mountain lion predation played a primary role in the outcome. Bighorns seek security in steep, perilous terrain. With their specially adapted hooves, they can leap from ledge to ledge, and traverse near vertical surfaces, at great speed. But it takes time for the animals to learn how to find food and water, and to navigate steep slopes or cliffs for safety in new terrain. Biologists believe that it may be important to reduce the risk of predation to improve the chances for the new herd to become established.
“We want to keep a close eye on these sheep to see how they're doing,” Wait said. “If we start seeing predation, we may need to step in to give these sheep some time to get established.”
Early this month, the DOW asked the Wildlife Commission for permission to remove individual mountain lions preying on the Middle Dolores herd for up to 24 months. Commissioners said that if a mountain lion kills more than one sheep, it should be removed, but that if a lion kills only one sheep, biologists would have the option to remove it. Prompt initiation of the control effort would help ensure that the individual lion responsible for the sheep predation is removed. If sheep leave the reintroduction area and are killed by a lion, no control action would take place. There have been no mortalities among the radio-collared sheep since their release on Dec. 17.
“Managing wildlife sometimes means making difficult choices,” Wait said. “In this case we know that the mountain lion population is stable in this area and some selective removal won't hurt it. But this will give the bighorns a chance to explore their new territory and get established before they have to worry about getting chased around by lions.”
The DOW will monitor the animals closely, and later this year, biologists will decide if a second transplant should take place.
For more information about bighorn sheep, visit http://wildlife.state.co.us/WildlifeSpecies/Profiles/Mammals/BighornSheep.htm