If you find yourself mucking around Filoha Meadows or up behind Sopris this spring, keep an eye peeled for bighorn sheep. If you’re lucky, you might catch yourself a glimpse of one of Colorado’s few indigenous herds. However, as sure-footed as the species is, Avalanche Creek’s herd stands on unsteady ground.
Over the years, disease has caused the herd to slowly dwindle. With a critical point on the horizon, Colorado Parks and Wildlife (CPW) is pensively considering its options.
District Wildlife Manager John Groves has been observing this group for the past two decades. In that time, he has seen a continuously steady decline.
“We’re currently looking at about 40-50 animals total left in that population, where historically we were at 250 plus — maybe more,” said Groves during a presentation at the Crystal River Caucus meeting in March.
The Avalanche herd has experienced a low lamb survivability rate for decades. In the past, those deaths have been attributed to various causes — including parasites — widening the scope of potential management strategies. Now that the science and data analysis has improved, CPW has identified the culprit: a bacterial pneumonia complex contracted by contact with domestic sheep.
Currently, CPW is seeing a 90-95% mortality rate with the lambs typically succumbing to the disease within a season of being born.
CPW attempted inoculating the herd against the complex with little success. Domestic sheep have also been removed from the area in order to eliminate the primary source of infection, but the disease continues to circulate among the wild lambs.
This is because the disease isn’t typically transmitted from domestic sheep directly to a lamb, but from healthier fully grown bighorns that carry the disease but haven’t succumbed to it — and sometimes won’t show any symptoms.
CPW is considering a “test and cull” method with the Avalanche herd in order to remove carrier sheep and give the lambs a better chance of survival. Over multiple years, members of the herd would be captured, tested and marked with trackers before being released. After several rounds of testing to identify chronic carriers, some of those carriers would be selectively euthanized to prevent further spreading of the disease.
This strategy hasn’t been used on this herd previously, but has been used on other herds throughout the West to some success.
In 2015, the test and cull protocol was performed on a similarly infected and declining herd in Hells Canyon, Idaho. That population did rebound. As a result of that success, the technique has been implemented along Idaho’s Salmon River, as well as in Washington and Oregon.
However, success is not guaranteed. Herd dynamics are different everywhere, and the specific disease complex can also vary from herd to herd. For an already low population, CPW has to delicately weigh their management options, while knowing that time is not on their side.
“If we have a high number of positive cases, we’re not going to go and just cull all of them,” said Groves. “If we get it wrong, then we’ve just wiped out a whole bunch of sheep that didn’t need to be.”
Translocation of new sheep into this population is theoretically possible, but that would cost the Avalanche Creek herd one of its most valuable attributes.
Avalanche Creek is host to a Tier One bighorn population, meaning that no substantial number of bighorns have been introduced to this herd. Only three herds in the state can claim the same. In Groves’ words, “This is the herd that’s always been there.” Translocating new sheep to Avalanche Creek could compromise the herd’s indigeneity.
For now, the question remains of how low a population can theoretically fall before rebounding. Groves stated that when a new herd is transplanted into an unpopulated area, wildlife managers typically introduce around 30 animals. So at least the Avalanche herd is still hovering above that baseline.
In short, CPW is between a rock and a hard place in figuring out how to keep this herd of sheep from the brink while still holding onto the indigeneity that makes it exceptional.
CPW faces tough call for sake of Avalanche Creek bighorns
