Wolves Return to Yellowstone

How was the decision made to reintroduce wolves into Yellowstone?

How are decisions made when there are so many different perspectives about bringing wolves back into an ecosystem? This was the dilemma in Yellowstone National Park in the 1990s, and is now the dilemma in Colorado. To anticipate discussions about reintroducing wolves into Colorado, let’s explore the robust debate that guided the 1994 decision-making process about whether or not to reintroduce wolves to Yellowstone. The US Fish and Wildlife Service (USFWS) took the lead in the decision-making process and held public meetings to gather citizen input.

What can we learn from the decision-making process used in Yellowstone? Working in USFWS teams, you will first sift through these citizen perspectives and then sort them by anticipated positions on wolf reintroduction. You will also learn more about the concept of ecosystem services (various benefits that nature provides to people and society) and compare these benefits to the potential negative ramifications of each wolf reintroduction scenario.


Sort Citizen Positions

How do different citizen groups feel about reintroducing wolves into Yellowstone?

Form USFWS teams of 3-4, and get a set of citizen statement cards. Divide them among your team like a deck of cards. Take turns reading cards. Discuss and predict how each citizen might feel about wolf reintroduction. Sort the cards into three groups: For Reintroduction, Against Reintroduction, Not a Clear Position. Create a table to keep a record of your thinking.


Identify the Ecosystem Benefits to People

How might ecosystem services affect our decision? 

Ecosystem services are the many benefits that nature provides to people and society. These benefits include, but are not limited to, clean water and air, crop pollination, nutritious food, nutrient-rich soil, and erosion protection. Ecosystems also provide recreational, cultural, and spiritual benefits.

  1. Gather more information about the four types of ecosystem services here:
  2. What ecosystem services can you identify in Yellowstone?
  3. What Yellowstone ecosystem services will be helpful to know about when comparing the wolf reintroduction scenarios? Why would this information be helpful?

Note: If you want to become more familiar with Yellowstone National Park, watch this video: Plan Your Visit from The National Park Service. 


Compare Proposed Reintroduction Scenarios

What are the pros and cons of different ways to reintroduce wolves into Yellowstone? 

Five different scenarios were considered for how to reintroduce wolves into Yellowstone:

  • Scenario 1: Reintroduction of experimental populations of wolves. The designation “experimental wolves”* gives the people who manage wolf populations more freedom in decision making and gives the wolves less protection.  
  • Scenario 2: Natural recovery (no action taken). Encourage wolf populations to naturally expand into Idaho and Yellowstone.  
  • Scenario 3: No wolves. Change laws in order to prevent wolf recovery.  
  • Scenario 4: Local wolf management committee. Turn wolf recovery management over to individual states and limit federal government involvement.  
  • Scenario 5: Reintroduction of non-experimental wolves.* By designating the wolves as “non-experimental” they are given much more protection.

*Note: The classifications of Scenario 1 as “experimental” and Scenario 5 as “non-experimental” are used in the Endangered Species Act of 1973. They help define how endangered or threatened species are managed in the United States.

Continuing in the role of the 1994 USFWS teams, you will do what they did - examine the feasibility of each scenario by charting pros and cons. As you do this, take into account citizen perspectives and the impacts on ecosystem services each scenario might have. Also consider any social, scientific, and economic constraints (limitations) for each scenario. Your USFWS team can modify scenarios to address any constraints or to increase support of ecosystem services.

  1. Read and discuss the pros and cons for each scenario on the handout Wolf Reintroduction Scenarios Pro and Con Chart.
  2. Highlight or underline the main points arguing for (pro) and against (con) each scenario. 
  3. Review the citizen statements and predict which scenario each would most likely support.  
  4. Create a separate table or matrix that summarizes citizen support for each scenario. You could include the name of the citizen role and a statement explaining why you think the role would support the scenario.

What was the impact of their decision? 

Think about the different wolf reintroduction scenarios you compared in the last section. The reintroduction scenario that was ultimately selected was #1, with a few modifications based on public comments. What were the impacts of this decision? 

Watch the full video of Wolves of Yellowstone | EARTH A New Wild. Watch the second half (2:39 minutes- end) several times to catch all the ecosystem connections described.

  • How have wolves impacted ecosystem services in Yellowstone? 
  • How have wolves affected the local economy? 
  • What has happened to other living organisms and nonliving parts of the ecosystem after reintroducing wolves? Create a second bubble concept map that shows these changes in the ecosystem. Start with a central bubble of “Wolves Reintroduced.” You can used this handout to record your answers. 

Revisit Trophic Cascades

How much ecosystem change can be attributed to the wolves’ return?

The following video has been instrumental in helping the public understand the significant impact an animal like the wolf can have on its ecosystem.

  1. Watch the video with a critical lens for accuracy based on what you’ve learned on this Quest. 
  2. Read the essay, "Scientists Debate: Do Wolves Change Rivers?" which summarizes current research on the relationship between the wolves’ return and a trophic cascade. 
  3. Complete Points to Ponder. 

Scientists Debate “Do Wolves Change Rivers?” 

It is widely agreed that taking wolves out of their ecosystems has caused a host of negative effects. The primary effect of wolf elimination was an increase in elk and deer populations that led to  overgrazing of woody trees like willow and aspen. This led to a reduction in beaver populations and degradation of rivers and riparian habitat. The animals that depended on these rivers, like birds and fish, were then affected negatively as well.  When wolves were reintroduced in Yellowstone, scientists identified positive effects like the restoration of woody tree species, gradual increases in beaver populations, and the improved health of rivers. However, the debate is about whether or not wolves were the sole driver of this restoration¹ ² ³. Research has uncovered other factors that also seem to be contributing to the positive shift⁴ ⁵. Water availability, effects of wolves on other predators, and human hunting all have been shown to have an effect on elk populations, and require further investigation⁶.  This is an important reminder that interactions among wolves, their prey, and the ecosystems’ vegetation are complex.  The common ground shared between both sides of this scientific debate is that the accurate story is way more complicated than the trophic cascade’s top-down, wolves-causing-ecosystem-rebalance-all-by-themselves explanation. In the field of ecology, each organism in an ecosystem plays a unique role. When one organism is removed, the rest of the ecosystem can be affected. If people help an organism return, the goal is not to restore the ecosystem to what it used to be, but to try to help improve or maintain the health of the ecosystem as it is now. The case study of Yellowstone suggests that restoring wolves to the landscape can help restore balance. It also indicates that more research needs to be done.  Even if their role as a main driver of the trophic cascade is debated, scientists agree that wolves are important to the ecosystem, and that bringing them back could push the ecosystem further towards a healthier balance.


  1. Is Science in Danger of Sanctifying the Wolf? from Biological Conservation (2012). https://doi.org/10.1016/j.biocon.2012.03.003
  2. Yellowstone Wolves and the Forces That Structure Natural Forces from Public Library of Science (2014). https://doi.org/10.1371/journal.pbio.1002025
  3. Trophic Cascades by Large Carnivores: A Case for Strong Inference and Mechanism from Trends in Ecology & Evolution (2015). https://doi.org/10.1016/j.tree.2015.09.012
  4. Has The Reintroduction Of Wolves Really Saved Yellowstone? from Popular Science (2014). https://www.popsci.com/article/science/have-wolves-really-saved-yellowstone/
  5. Rethinking predators: Legend of the wolf from Nature News (2014). https://www.nature.com/articles/507158a
  6. The Big Scientific Debate: Trophic Cascades from MacNulty Lab (2014). https://qcnr.usu.edu/labs/macnulty_lab/files/Smith%20et%20al%202016a.pdf

Points to Ponder

  1. The video claims that the wolf’s return caused a trophic cascade. What does this mean? 
  2. What evidence does the video give to support its claim that wolves have caused a change in the rivers? 
  3. The narrator inaccurately refers to the hoofed prey as “deer.” What is this animal? 
  4. What other statements were made that would be helpful to confirm from other sources?
  5. The text describes how some recent and ongoing research does not support the wolf trophic cascade hypothesis. Describe these research findings. 
  6. Even though scientists are not all in agreement that wolves are the direct cause of all the positive ecosystem changes described in the video, what do scientists agree on?
educator note

This Quest modifies and shortens Part 2 from the existing lesson plan (p. 12-18). Students will work in US Fish and Wildlife teams in a modified analysis of the Yellowstone decision-making. Then they will use this experience to simulate a Colorado Public Forum to express citizen perspectives on reintroducing wolves into Colorado’s mountains. 

Wolves of Yellowstone Teacher Guide. Continue using the teacher guide and download Part 2 support materials. Answer keys to activity pages are here. The scenario ultimately chosen was a modification of #1. 

Video: Wolves of Yellowstone: A New Wild (5:30 minutes) 

This video is divided into two parts. On this webpage, you will show the entire video, allowing students to watch the second half (2:36-end) several times. It describes the park after the wolves were reintroduced. Students have already seen the first half (0-2:36 minutes) of the video for an activity on the previous webpage. It talks about Yellowstone without wolves. 

Student handout, Part 2 worksheet, was modified for the Quest. The original is here.

Student handout, Part 2 Student Worksheet: Student Role-Playing Materials — Scenarios Matrix, has been modified for the Quest. The pages have been separated and recombined to support different Quest lessons. You can see them in original form here.

Supporting resource