The bighorn sheep of Jackson, Wyoming, is facing a serious threat that has been observed over the years. According to a study conducted by the Wyoming Game and Fish Department (WGFD) and the University of Wyoming (UW), the population of the Jackson bighorn sheep herd is vulnerable to a pneumonia die-off when the population reaches around 500 sheep.
This pattern has been observed for many years, and as the population grows, the chances of a die-off increase. The WGFD/UW study, which began in 2015, is the first of its kind to study Rocky Mountain bighorn sheep.
Despite good nutrition levels between 2015 and 2019, data from the past three years shows a noticeable drop in the herd’s body condition. This is particularly shocking coming out of summer. Wildlife biologist Aly Courtemanch says, “That’s what we would expect for a population that’s reaching or exceeding its carrying capacity on the landscape. If history repeats itself, we’re setting ourselves up for another pneumonia crash.”
The hypothesis from the study is that as the bighorn sheep population exceeds the habitat’s carrying capacity, a reduction of available nutrition and corresponding weakened body conditions make the herd more susceptible to pneumonia. Pneumonia was originally transmitted to Jackson bighorn sheep from domestic sheep and is constantly circulating through the Jackson herd population.
Population Caps Needed?
To support the herd, the WGFD is considering hunting bighorn sheep when the data shows the sheep are in poor condition. This can help manage the population and avoid a major die-off. However, enhancing habitat through prescribed burns, mowing sagebrush, and invasive plant species control may help. But those take a long time to implement and are not allowed in wilderness areas. Unfortunately, that’s where this herd spends most of its time.
Although the Jackson herd is showing a slightly elevated mortality rate this winter, the WGFD expects most of the bighorn sheep will survive this winter, even with low levels of body fat.
In conclusion, the Jackson bighorn sheep herd is facing a serious threat of pneumonia die-offs when the population reaches around 500 sheep. Hunting is a great management tool to keep the population stable. However, enhancing habitat carrying capacity is crucial in the long term to support the herd’s health. This study is currently ongoing. That means that WGFD and UW will continue to monitor and evaluate the Jackson herd.