Predicting the effects of supplemental feeding and chronic wasting disease in Greater Yellowstone Ecosystem elk
To support management decisions concerning 500 bison and 8,000 elk in Jackson, Wyoming, USGS scientists assessed how alternative U.S. Fish and Wildlife Service plans for providing supplemental food would influence: 1) chronic wasting disease prevalence, 2) elk and bison numbers, 3) wildlife movement and human-wildlife conflict 4) multiple use opportunities for the public, like hunting, and 5) costs of running the program.
The National Elk Refuge & Supplemental Feeding
- During the winter, the NER provides supplemental food to approximately 8,000 elk and 500 bison from January through March.
- Supplemental feeding leads to potential tradeoffs between:
- Creating dense aggregations of animals that may increase disease transmission,
- Reducing winter starvation, and
- Reducing conflicts on private property
- The US Forest Service (USFS) and National Park Service (NPS) administer most of the land within the study area (see map inset for regional perspective).
- Core elk winter range mainly consists of the NER (FWS), State, and private lands.
- Click on map to enlarge.
Jackson elk migrate across federal, state, and public lands:
- Short-distance migrants (dark blue) spend summer on private property or in areas of Grand Teton National Park west of the NER.
- Long-distance migrants (light blue) mostly spend summer on public lands.
- Click on map to enlarge.
Background image shows an example of the refuge's diverse habitats—Sheep Mountain (not part of the refuge) is in the background.
Chronic Wasting Disease
Chronic Wasting Disease (CWD) is a lethal disease caused by misfolded proteins called prions that affects deer, elk, and moose.
- CWD is a growing management issue that has been detected in at least six countries, four Canadian provinces, and 35 U.S. states (as of January 2025).
- CWD was detected in Grand Teton National Park in 2018 in a mule deer and in 2020 in an elk.
- Click on map to enlarge.
- Animals are infected through direct contact with infectious animals or through contact with a contaminated environment.
- Prions can remain infectious in the soil for many years.
- There are currently no effective treatments or vaccines.
- Experts expect that supplemental winter feeding of elk could increase direct and indirect CWD transmission by 2-4 times.
The Role of USGS Science in Evaluating the Use of Supplemental Feed at the NER
- The FWS and its partners are currently assessing the continued winter feeding of elk and bison on the NER to inform a National Environmental Policy Act environmental impact statement associated with developing the next Bison and Elk Management Plan for the refuge.
- USGS scientists, in collaboration with the FWS, facilitated and conducted a structured decision-making process to identify key FWS objectives and multiple potential management alternatives to be evaluated.
- USGS scientists used a combination of models and expert panels to assess how those management alternatives may affect FWS objectives.
- This work was supported through many years of previous research conducted by USGS, its partners, and collaborators.
CWD Research—USGS & Partners
USGS CWD Research-Report
USGS CWD Research Projects
USGS Disease Decision Analysis & Research Group
A Collaborative Effort
This work was supported by subject matter expert teams and expert panels who met for over a year in weekly to monthly meetings.
- The subject matter expert teams included wildlife, physical landscapes, and socioeconomics
- The expert panels were on elk movement and bison population dynamics
- FWS, USFS, NPS, and Wyoming Game and Fish Department staff served on both expert teams and expert panels; USGS staff served on expert teams
Objectives & Management Alternatives
The FWS has multiple objectives for the management of bison and elk on the NER, including the animals themselves, wildlife disease, private property-wildlife conflicts, refuge visitors, local economies, and vegetation.
The objectives were:
- Maximize the health and well-being of wildlife
- Maintain ecosystem fluctuations and processes associated with bison and elk
- Minimize risk of invasive species introduction associated with bison and elk management activities
- Protect and restore the chemical, physical, and biological quality of water resources
- Maintain and enhance multiple use opportunities and public enjoyment
- Minimize human-wildlife conflicts
- Minimize costs of bison and elk management activities
- Maximize local economic benefits associated with bison and elk presence on the NER and surrounding lands
- Maximize opportunities for Tribes to engage in activities related to their buffalo culture
The management alternatives that were evaluated in this study were:
- Continue supplement feeding of bison and elk on the NER (Continue feeding)
- Stop supplemental feeding (Stop or No feeding)
- Stop feeding after CWD (disease) 3%
- Reduce and then stop feeding
- Increase harvest of elk to reduce their population, then stop feeding
This webpage will cover the results of the continued feeding vs. no feeding management alternatives in the context of many of the wildlife-focused objectives, public use/activities objectives, and the cost objective. If you are interested in seeing all the results of the study please see the USGS report for those details.
Background image is an aerial view of elk at the NER after being provided supplemental feed.
Results—Elk Population Size & CWD Prevalence
USGS scientists developed models of elk and bison population dynamics, CWD, and elk movement. These models were run many times to assess the uncertainty in their predictions.
Elk population size and CWD prevalence
These figures show bold lines depicting the average of 100 model runs.
- The no feeding alternative resulted in an initial reduction in population size as elk:
- moved to other areas
- were subjected to more winter mortality
- After 20 years, however, the no feeding alternative resulted in:
- less CWD and higher elk population size than Continued feeding
- Click on figure to enlarge.
Models were run many times to incorporate varying environmental conditions and uncertainty in model parameters.
- Fine lines represent the outcomes over a 20-year time window of the 100 times the models were run and enables people to visualize the range or variation of potential outcomes
- The bold lines are the the same as those in the figure above and depicts the average of 100 simulations.
- Click on figure to enlarge.
Going forward, only the average of the model simulations will be shown to make viewing the results easier. To see the variation of all the potential outcomes evaluated, see the USGS Report.
Work by Galloway et al. (2021) suggests that the NER elk population may decline with less CWD (around 7%) than what was projected in this USGS report.
Results—Elk Movement Across the Landscape
Elk distribution
Ending winter supplemental feeding on the NER may result in elk moving onto private lands and increasing wildlife-human conflict. Expert knowledge informed where some elk would go if feeding stopped and the elk CWD model provided the numbers of elk being distributed across the study area at monthly timesteps.
- Data from radiocollared elk were used to develop habitat selection models. Those models and expert knowledge led to a prediction that elk would spend more time on private property and in the Gros Ventre river drainage (Forest Service land) if feeding stops at the NER.
- Experts predicted that of elk currently fed at the NER:
- 50% of the elk would continue to return there even without feeding,
- 14% would move to the Fall Creek feedgrounds (Forest Service land),
- 18% would move to the Gros Ventre drainage feedgrounds
- 19% would move to other winter ranges of the Jackson Herd unit.
- Use slider on image below to compare elk distribution under the continued feeding and no feeding management alternatives; click on image to enlarge.
- Image on left shows land holdings—the National Elk Refuge is managed by the FWS.
Results—Recreational Opportunities for the Public
The effects of continued feeding and no feeding management alternatives on elk hunting
The public benefits from the elk at the NER in a variety of ways including hunting and outfitting, and winter tourism at the NER that includes winter visitors and horse-drawn sleigh rides that get customers near elk. The effects of the management alternatives were evaluated on these multiple use opportunities for the public
- Models predicted that both the elk population (see above) and number hunted would decline.
- Those declines were more severe for the continued feeding alternative (up to 75% decline).
- By year 20, CWD mortalities were predicted to be equal or greater than the number hunted.
- Click figure to enlarge.
Effects of supplemental feeding management alternatives on NER winter visitation
- There was only weak support for a relationship between elk counts and NER winter visitation.
Results—Bison Response
Bison population and hunting responses to management alternatives
The bison are the national mammal of the U.S. and were once distributed across North America before they approached extinction due to overharvesting in the late 1800s. The current population of around 500 bison moves freely between the NER and Grand Teton National Park and is fed at the NER during the winter. Altering the supplemental feeding of bison may impact bison population size, human-bison conflicts, and the ability for hunters to harvest bison. Neither bison nor cattle are thought to be susceptible to CWD.
Model results predict that the bison population and number hunted would decline if feeding on the NER were to stop (top panels below).
Human conflicts with bison were predicted to increase substantially in the years immediately following the elimination of feeding, but may decline over time as managers and the public learn how to reduce those conflicts (bottom panel below).
- Examples of human-bison conflicts include:
- Vehicle collisions
- Grazing on cattle lands
- Overgrazing of sensitive habitats
- Click on figure to enlarge.
- The bison population size figure provides a visualization of the variation or range of the modeling results by showing each model result as a fine line (bold lines depict the average of all model runs).
Background image depicting bison being fed at the NER.
Results—Costs
Estimating the monetary cost of the elk and bison winter supplemental feeding program
Running the winter supplemental feed program at the NER has costs that include the feed, labor, fuel and maintenance for machinery. The study estimated the monetary cost to the FWS of continuing the winter supplemental feeding program.
Assuming an average 62 day feeding season:
- The continued feeding alternative was estimated to cost, on average, $19.3 million over 20 years.
- Indirect costs from increased mitigation of human-wildlife conflict or culling of ill elk, and private property damage costs were not quantified.
Summary
The USGS report quantified the expected effects of the arrival of CWD and tradeoffs associated with the supplemental feeding program at the NER.
- Winter supplemental feeding can increase disease transmission and impacts but also reduces neighboring private property damage caused by elk and bison.
- Stopping feeding may result in short term losses of elk and increased social conflict, but likely reduces future impacts of CWD and results in a larger elk population size over time compared to continued feeding.
- FWS and collaborating agencies are using the results of the USGS report to further tailor their management alternatives considered in the next Bison and Elk Management Plan.
- See here for current information on the Elk and Bison Management Plan: https://www.fws.gov/NER-BEMP
Disease Decision Analysis and Research
USGS Chronic Wasting Disease Research at NOROCK
To support management decisions concerning 500 bison and 8,000 elk in Jackson, Wyoming, USGS scientists assessed how alternative U.S. Fish and Wildlife Service plans for providing supplemental food would influence: 1) chronic wasting disease prevalence, 2) elk and bison numbers, 3) wildlife movement and human-wildlife conflict 4) multiple use opportunities for the public, like hunting, and 5) costs of running the program.
The National Elk Refuge & Supplemental Feeding
- During the winter, the NER provides supplemental food to approximately 8,000 elk and 500 bison from January through March.
- Supplemental feeding leads to potential tradeoffs between:
- Creating dense aggregations of animals that may increase disease transmission,
- Reducing winter starvation, and
- Reducing conflicts on private property
- The US Forest Service (USFS) and National Park Service (NPS) administer most of the land within the study area (see map inset for regional perspective).
- Core elk winter range mainly consists of the NER (FWS), State, and private lands.
- Click on map to enlarge.
Jackson elk migrate across federal, state, and public lands:
- Short-distance migrants (dark blue) spend summer on private property or in areas of Grand Teton National Park west of the NER.
- Long-distance migrants (light blue) mostly spend summer on public lands.
- Click on map to enlarge.
Background image shows an example of the refuge's diverse habitats—Sheep Mountain (not part of the refuge) is in the background.
Chronic Wasting Disease
Chronic Wasting Disease (CWD) is a lethal disease caused by misfolded proteins called prions that affects deer, elk, and moose.
- CWD is a growing management issue that has been detected in at least six countries, four Canadian provinces, and 35 U.S. states (as of January 2025).
- CWD was detected in Grand Teton National Park in 2018 in a mule deer and in 2020 in an elk.
- Click on map to enlarge.
- Animals are infected through direct contact with infectious animals or through contact with a contaminated environment.
- Prions can remain infectious in the soil for many years.
- There are currently no effective treatments or vaccines.
- Experts expect that supplemental winter feeding of elk could increase direct and indirect CWD transmission by 2-4 times.
The Role of USGS Science in Evaluating the Use of Supplemental Feed at the NER
- The FWS and its partners are currently assessing the continued winter feeding of elk and bison on the NER to inform a National Environmental Policy Act environmental impact statement associated with developing the next Bison and Elk Management Plan for the refuge.
- USGS scientists, in collaboration with the FWS, facilitated and conducted a structured decision-making process to identify key FWS objectives and multiple potential management alternatives to be evaluated.
- USGS scientists used a combination of models and expert panels to assess how those management alternatives may affect FWS objectives.
- This work was supported through many years of previous research conducted by USGS, its partners, and collaborators.
CWD Research—USGS & Partners
USGS CWD Research-Report
USGS CWD Research Projects
USGS Disease Decision Analysis & Research Group
A Collaborative Effort
This work was supported by subject matter expert teams and expert panels who met for over a year in weekly to monthly meetings.
- The subject matter expert teams included wildlife, physical landscapes, and socioeconomics
- The expert panels were on elk movement and bison population dynamics
- FWS, USFS, NPS, and Wyoming Game and Fish Department staff served on both expert teams and expert panels; USGS staff served on expert teams
Objectives & Management Alternatives
The FWS has multiple objectives for the management of bison and elk on the NER, including the animals themselves, wildlife disease, private property-wildlife conflicts, refuge visitors, local economies, and vegetation.
The objectives were:
- Maximize the health and well-being of wildlife
- Maintain ecosystem fluctuations and processes associated with bison and elk
- Minimize risk of invasive species introduction associated with bison and elk management activities
- Protect and restore the chemical, physical, and biological quality of water resources
- Maintain and enhance multiple use opportunities and public enjoyment
- Minimize human-wildlife conflicts
- Minimize costs of bison and elk management activities
- Maximize local economic benefits associated with bison and elk presence on the NER and surrounding lands
- Maximize opportunities for Tribes to engage in activities related to their buffalo culture
The management alternatives that were evaluated in this study were:
- Continue supplement feeding of bison and elk on the NER (Continue feeding)
- Stop supplemental feeding (Stop or No feeding)
- Stop feeding after CWD (disease) 3%
- Reduce and then stop feeding
- Increase harvest of elk to reduce their population, then stop feeding
This webpage will cover the results of the continued feeding vs. no feeding management alternatives in the context of many of the wildlife-focused objectives, public use/activities objectives, and the cost objective. If you are interested in seeing all the results of the study please see the USGS report for those details.
Background image is an aerial view of elk at the NER after being provided supplemental feed.
Results—Elk Population Size & CWD Prevalence
USGS scientists developed models of elk and bison population dynamics, CWD, and elk movement. These models were run many times to assess the uncertainty in their predictions.
Elk population size and CWD prevalence
These figures show bold lines depicting the average of 100 model runs.
- The no feeding alternative resulted in an initial reduction in population size as elk:
- moved to other areas
- were subjected to more winter mortality
- After 20 years, however, the no feeding alternative resulted in:
- less CWD and higher elk population size than Continued feeding
- Click on figure to enlarge.
Models were run many times to incorporate varying environmental conditions and uncertainty in model parameters.
- Fine lines represent the outcomes over a 20-year time window of the 100 times the models were run and enables people to visualize the range or variation of potential outcomes
- The bold lines are the the same as those in the figure above and depicts the average of 100 simulations.
- Click on figure to enlarge.
Going forward, only the average of the model simulations will be shown to make viewing the results easier. To see the variation of all the potential outcomes evaluated, see the USGS Report.
Work by Galloway et al. (2021) suggests that the NER elk population may decline with less CWD (around 7%) than what was projected in this USGS report.
Results—Elk Movement Across the Landscape
Elk distribution
Ending winter supplemental feeding on the NER may result in elk moving onto private lands and increasing wildlife-human conflict. Expert knowledge informed where some elk would go if feeding stopped and the elk CWD model provided the numbers of elk being distributed across the study area at monthly timesteps.
- Data from radiocollared elk were used to develop habitat selection models. Those models and expert knowledge led to a prediction that elk would spend more time on private property and in the Gros Ventre river drainage (Forest Service land) if feeding stops at the NER.
- Experts predicted that of elk currently fed at the NER:
- 50% of the elk would continue to return there even without feeding,
- 14% would move to the Fall Creek feedgrounds (Forest Service land),
- 18% would move to the Gros Ventre drainage feedgrounds
- 19% would move to other winter ranges of the Jackson Herd unit.
- Use slider on image below to compare elk distribution under the continued feeding and no feeding management alternatives; click on image to enlarge.
- Image on left shows land holdings—the National Elk Refuge is managed by the FWS.
Results—Recreational Opportunities for the Public
The effects of continued feeding and no feeding management alternatives on elk hunting
The public benefits from the elk at the NER in a variety of ways including hunting and outfitting, and winter tourism at the NER that includes winter visitors and horse-drawn sleigh rides that get customers near elk. The effects of the management alternatives were evaluated on these multiple use opportunities for the public
- Models predicted that both the elk population (see above) and number hunted would decline.
- Those declines were more severe for the continued feeding alternative (up to 75% decline).
- By year 20, CWD mortalities were predicted to be equal or greater than the number hunted.
- Click figure to enlarge.
Effects of supplemental feeding management alternatives on NER winter visitation
- There was only weak support for a relationship between elk counts and NER winter visitation.
Results—Bison Response
Bison population and hunting responses to management alternatives
The bison are the national mammal of the U.S. and were once distributed across North America before they approached extinction due to overharvesting in the late 1800s. The current population of around 500 bison moves freely between the NER and Grand Teton National Park and is fed at the NER during the winter. Altering the supplemental feeding of bison may impact bison population size, human-bison conflicts, and the ability for hunters to harvest bison. Neither bison nor cattle are thought to be susceptible to CWD.
Model results predict that the bison population and number hunted would decline if feeding on the NER were to stop (top panels below).
Human conflicts with bison were predicted to increase substantially in the years immediately following the elimination of feeding, but may decline over time as managers and the public learn how to reduce those conflicts (bottom panel below).
- Examples of human-bison conflicts include:
- Vehicle collisions
- Grazing on cattle lands
- Overgrazing of sensitive habitats
- Click on figure to enlarge.
- The bison population size figure provides a visualization of the variation or range of the modeling results by showing each model result as a fine line (bold lines depict the average of all model runs).
Background image depicting bison being fed at the NER.
Results—Costs
Estimating the monetary cost of the elk and bison winter supplemental feeding program
Running the winter supplemental feed program at the NER has costs that include the feed, labor, fuel and maintenance for machinery. The study estimated the monetary cost to the FWS of continuing the winter supplemental feeding program.
Assuming an average 62 day feeding season:
- The continued feeding alternative was estimated to cost, on average, $19.3 million over 20 years.
- Indirect costs from increased mitigation of human-wildlife conflict or culling of ill elk, and private property damage costs were not quantified.
Summary
The USGS report quantified the expected effects of the arrival of CWD and tradeoffs associated with the supplemental feeding program at the NER.
- Winter supplemental feeding can increase disease transmission and impacts but also reduces neighboring private property damage caused by elk and bison.
- Stopping feeding may result in short term losses of elk and increased social conflict, but likely reduces future impacts of CWD and results in a larger elk population size over time compared to continued feeding.
- FWS and collaborating agencies are using the results of the USGS report to further tailor their management alternatives considered in the next Bison and Elk Management Plan.
- See here for current information on the Elk and Bison Management Plan: https://www.fws.gov/NER-BEMP