The population of Colorado's iconic bighorn sheep herds in the Maroon Bells-Snowmass Wilderness has plummeted over the past 15 years. Officials from Colorado Parks and Wildlife are trying to determine why.
The wildlife division temporarily captured 10 bighorn rams last week and placed collars fitted with global positioning systems on them. Officials from the wildlife division and the U.S. Forest Service will monitor the movements and distribution of the rams. They want to learn if rams from different herds interact with ungulates from other herds, and they want to see if they cross areas allotted for domestic sheep, according to Julie Mao, terrestrial biologist for Colorado Parks and Wildlife in Glenwood Springs.
The bighorn sheep are dying from respiratory disease possibly caused by bacterial pneumonia, according to the wildlife division. Two of the three herds in the wilderness area have been hit hard. Little is known about the third herd.
Bighorns known as the Avalanche herd, because of the time they spend along Avalanche Creek between Carbondale and Redstone, have dropped in numbers by more than 50 percent in 10 to 15 years, according to Perry Will, wildlife manager for Area 8, which includes the Roaring Fork River basin. The Avalanche herd once had 80 to 100 animals and maybe more, he said. It's now at 40.
The wildlife division and a contractor used a spotter airplane and a helicopter last week to capture the rams. They were found in Avalanche Creek, near Marble, at the head of the Conundrum Valley and closer to Crested Butte, Will said.
Nets that are about 12 by 20 feet were shot from guns in the helicopters. The rams got tangled and then were hobbled, fit with the collars and released. The process, called "net gunning," is critical to reducing the chase time and, therefore, the stress on the rams, Will said. All 10 rams were fit with collars on the same day.
The collars send out a signal every few hours, allowing them to be tracked. When the frequency of sending signals is spread out, the collars last longer, Will said. This project could continue for two years.
Rams are the focus of the study because they generally travel farther than ewes, according to the wildlife division. If infected, the rams could transmit disease to uninfected wild sheep when they return to their herds.
Learning more about the rams' movements might help wildlife and livestock managers minimize the amount of inter-species contact, keeping potential disease transmission to a minimum, according to a statement from the agency. It's suspected that bighorn sheep pick up diseases from domestic sheep.
The Forest Service is a partner in the project. It will work with livestock producers in the area to collar and monitor domestic sheep.
"We will focus on limiting interactions, and we anticipate good results from this strategy," Will said.
Funding for the study came from the Rocky Mountain Bighorn Society, Colorado's Auction and Raffle Program and the Wild Sheep Foundation.
While populations are dropping in at least two of the three herds in and around the Crystal River Valley, the numbers are holding steady in the Fryingpan Valley herd outside Basalt.
"The Fryingpan herd is doing as well as any in the state," Will said. He estimated there are 80 to 100 bighorns in that herd.
The population in the Fryingpan is deemed strong enough that a handful of animals will be captured this summer and reintroduced to Gore Canyon, near Kremmling, Will said. Bighorns from the Fryingpan were relocated three years ago to help build the population in Gore Canyon. Those numbers haven't climbed as rapidly as wildlife managers want, so they plan to introduce additional bighorns to the herd, Will said.