Killing off sick bighorns aided herds, officials say

MISSOULA – A spring survey of bighorn sheep showed that efforts to prevent a pneumonia outbreak by killing the sick animals appeared to help more lambs survive, according to Montana wildlife managers.

“The idea was to kill the last sick sheep before it infected the next healthy sheep,” Mike Thompson of Montana Fish, Wildlife and Parks told the Missoulian.

“The overall situation is tough,” he said. “But the choices we made seem to be bearing some fruit.”

Thompson said the rate of survival for lambs was about 30 percent in two herds where sick sheep were killed. That was an increase from the rate of 2 percent in two herds where culling efforts were halted because of difficult terrain.

Officials said the pneumonia outbreak since late 2009 has killed more than 500 bighorn sheep in Western Montana. In the Bonner and East Fork Bitterroot herds where sheep were killed, 179 were slaughtered to prevent others from getting sick.

The herds where terrain halted the efforts were the upper and lower Rock Creek herds.

Thompson said the culling also likely prevented three other bighorn herds from becoming infected with pneumonia.

“That helped buffer those populations and keep it from spreading,” he said.

Two other herds that were infected experienced heavy losses. A survey by biologist Ray Vinkey of Fish, Wildlife and Parks found 104 sheep in the Lost Creek herd in May, down from 297 last year.

Near Garrison, Vinkey counted 57 sheep, down from 118 in 2005.

Culling efforts in those two herds to prevent the spread of pneumonia was halted, Thompson said, because the disease was too advanced.