Feeding Elk in Winter vs. Chronic Wasting Disease: USGS Models for Western Wyoming

In western Wyoming, elk are fed through the winter to keep herds alive, to keep them off private land, and to limit the spread of brucellosis from elk to cattle. That matters to ranchers: if brucellosis turns up in cattle, the U.S. Department of Agriculture requires the whole herd to be euthanized or quarantined until it passes several negative tests. But feeding may also speed the spread and effects of chronic wasting disease (CWD), which has no treatment or vaccine, is always fatal, and can stay infectious in the environment for many years.

In 2023 the U.S. Geological Survey, working with the Forest Service and the U.S. Fish and Wildlife Service, weighed the costs and benefits of four feeding options, with implications for the whole Greater Yellowstone Ecosystem.

Elk being fed at a Wyoming Game and Fish Department feedground. USGS photo.

The background

• More than 75 percent of the Greater Yellowstone Ecosystem's elk are fed in winter, in the western Wyoming herd units that have feedgrounds.
• Seven of the Wyoming Game and Fish Department's feedgrounds are on Forest Service land, and their permits are under review or expire by 2028.
• Feeding packs elk densely together, which likely helps CWD spread. CWD was first found in Grand Teton National Park in deer in 2018 and in elk in 2020.
• Deer and elk are prey for grizzly bears, cougars, wolves and black bears, and hunting them supports local economies. CWD has been linked to declines of mule deer and white-tailed deer in Wyoming, but it moves slowly, taking years to decades to infect more than 20–30 percent of a population.

The study informed the Forest Service's draft environmental impact statement for two permitted feedgrounds, Dell Creek and Forest Park, and also looked at closing all feedgrounds, or only the Forest Service ones, in the five herd units south of Jackson: Fall Creek, Upper Green River, Afton, Piney and Pinedale. Separately, the Fish and Wildlife Service is deciding the future of feeding at the National Elk Refuge near Jackson, where roughly 600 bison and 8,000 elk are fed each winter.

Supplemental elk feedgrounds and herd units in western Wyoming evaluated by USGS. USGS.

Options and goals

Using structured decision making, which breaks a complex problem into parts, the Forest Service, USGS and the Fish and Wildlife Service set out four alternatives — no feeding, continued feeding, emergency-only feeding, and phasing feeding out after 3 years — and six objectives: minimize disease in elk; maintain elk numbers; maximize hunting opportunity; maintain other big game; minimize conflict with agriculture and the public; and maximize the prosperity of resource-based economies.

Computer models projected CWD, elk numbers and hunting revenue for 20 years after the Forest Service decision, which was still pending as of November 2024. Spatial models estimated damage to private property and the risk of brucellosis reaching cattle.

What the models found

A panel of state, federal and academic experts judged that CWD transmission would likely be several times higher among fed elk. Fed into USGS models, that gave:

Modeled CWD prevalence over 20 years in (A) a fed and (B) an unfed elk population. USGS.

Because each herd unit has several feedgrounds, and about a quarter of the elk in those units never use them, changing one feedground did little: Dell Creek and Forest Park feed only 12–20 percent of the Upper Green River and Afton elk. Effects grew when the same choice applied to many feedgrounds. Across all five units south of Jackson:

• Continued feeding led to a 58 percent drop in elk by 2044 as CWD rose, but carried the smallest brucellosis risk to cattle.
• No feeding caused bigger early declines — more conflict on private land and lower survival where winter range is short — but a smaller decline by 2044, 35 percent, because CWD stayed lower. It also produced more elk harvested over the 20 years, more tag sales and more regional economic input.
• A 3-year phaseout suggested that even short delays in closing feedgrounds mean more CWD than acting at once.

Modeled elk numbers over time, summed across the five herd units, under ending or phasing out feeding. USGS.

Sources

Rewritten from the U.S. Geological Survey Fact Sheet 2024–3046, "Potential effects of chronic wasting disease and supplemental feeding on elk populations in Wyoming" (public domain), summarizing Cook and others (2023), USGS Open-File Report 2023–1015, in hubnx's own words.