Gray Wolves

Yellowstone National Park and The Future

William Georgenes - ENVS 117 at Santa Clara University

December 8th, 2022


The Gray Wolf population in Yellowstone National Park has undergone a significant change in recent years. Once nearly eradicated from the region, conservation efforts have helped the gray wolf population make a significant recovery. As of the Yellowstone Wolf Project’s 2021 annual report, there are 97 Gray Wolves living in the park which play a crucial role in maintaining the balance of the park’s ecosystem (National Parks Service, 2021). Much has changed within Yellowstone National Park since the introduction of the wolves, and I hope to find out more about how the wolves have moved in space and size and how we can prolong the beneficial effects and potentially apply similar interventions in other ecosystems.

Wolf Facts

Genus: Canis (Latin word meaning “dog”)
Species: lupus (Greek word meaning “wolf”)
Average body mass: males 110 pounds (50 kg); females 90 pounds (41 kg)
Primary food sources in Yellowstone: Winter: elk (>96%), bison (3-4% and increasing in recent years; deer (1.5%); Spring: elk (89%), bison (7%), deer (7.1%); Summer: elk (85%), bison (14.1%), deer (<1%)
Elk killed per year per wolf: 18-22 elk/wolf/year
Average lifespan in Yellowstone: 4-5 years

Sources: (National Parks Service, 2022) and (Almberg ES, 2011)

What is a Keystone Species?

A keystone species has a disproportionately large impact on its environment relative to its abundance. This means that even though it may not be the most abundant species in an ecosystem, it plays a crucial role in maintaining the balance of that ecosystem. If a keystone species is removed from an ecosystem, a chain of events will occur that drastically changes the structure and biodiversity of that ecosystem (Denchak , 2022). There are three types of keystone species: predators, ecosystem engineers, and mutualists. Predators control the population of pray species. Example: Gray Wolf. Ecosystem engineers are species that create, control, and destroy a habitat. Example: Beaver. Mutualists are when multiple species interact in a beneficial symbiotic way that benefits everyone. Example: Bees (National Geographic Society, 2022).


Data from The National Park Service allows us to look at and analyze the movement of gray wolves and the territories of each pack on Yellowstone Park over time, starting from the introduction in 1995. The population of gray wolves has fluctuated and packs of wolves have been created and others have dispersed over the years. Population and location data can help us better understand the Yellowstone National Park ecosystem with the addition of gray wolves and what we can do to maintain and improve the ecosystem going forward.

Wolf Pack Movement

Wolf packs are groups of wolves that live and hunt together. They typically consist of a breeding pair of wolves, known as the alpha male and alpha female, and their offspring. The size of a wolf pack can vary, but in Yellowstone National Park, the average pack size is 11.8 individuals (U.S. Department of the Interior). Wolf packs have complex social structures and communication systems, and they are known for their intelligence and adaptability. Territory is always part of the competition. The most desired areas are the ones with the most prey. In the first five years that the wolves were introduced to the park, around three quarters of their diet had been elk, but recently, bison has been becoming a more popular food source. The diet of gray wolves in the park is closely tied to the availability of prey, and it may vary depending on the time of year, but it is the main reason the packs compete for territory.

Take a look at these interactive maps of the wolf pack territories In Yellowstone National Park in 1995, 2007, 2015, 2019 to see the formation, disappearance, and movement of the packs. Hover your cursor over the different shaded regions to see the name of the pack. Alternatively, view the key below the figures.

Figure 1. Wolf pack territories in Yellowstone Park in 1995

These were the packs formed from the original 31 wolves that were placed in Yellowstone Park. Nine pups were born in the spring of 1995, and 14 in the spring of 1996. This began the rise of the gray wolf population for the next several years.

Figure 2. Wolf pack territories in Yellowstone Park in 2007

The wolf population in 2007 is 171, one of it’s highest recorded years since introduction.

Figure 3. Wolf pack territories in Yellowstone Park in 2015