Yellowstone National Park is home to the grizzly bear, an iconic animal whose population numbers indicate the ecosystem’s health. Yellowstone and the surrounding Greater Yellowstone Ecosystem (GYE) provide vital habitat for these bears, representing the success of conservation efforts.
Yellowstone’s Current Grizzly Population
The grizzly bear population within the Greater Yellowstone Ecosystem has shown significant growth, reaching an estimated peak of 1,030 individuals in 2024. A new integrated population model, launched in 2023, initially predicted around 965 grizzlies within the demographic monitoring area. These numbers are estimates, reflecting the complexities of counting a wide-ranging species across vast, rugged terrain. The GYE grizzly bear population is recognized as a distinct population segment for management purposes.
Methods for Counting Grizzlies
Estimating grizzly bear numbers relies on scientific methods employed by the Interagency Grizzly Bear Study Team (IGBST), a collaborative group of federal, state, and tribal agencies. Historically, the IGBST used the “Chao2 method,” which involved counting females with cubs-of-the-year (COY) through aerial and ground observations. This approach extrapolated the total population by applying survival and reproduction rates, but often underestimated the true population size.
To enhance accuracy, a more sophisticated “integrated population model” was developed starting in 2018 and fully launched in 2023. This advanced model incorporates a wider range of data, including census information, reproductive rates, and longevity. It also utilizes data from radio-collared bears and visual observations, allowing for more reliable population estimates.
Historical Trends and Population Recovery
The history of grizzly bears in the Yellowstone area reflects a remarkable recovery from near extinction. In the mid-20th century, their numbers plummeted due to human persecution and habitat loss. By 1975, the GYE population was estimated as low as 136 bears. This decline led to their listing as a threatened species under the Endangered Species Act (ESA) in 1975.
Following ESA protection, intensive conservation efforts spurred a substantial recovery, with the population more than quadrupling over the decades. By 2016, grizzlies had rebounded to approximately 700. Recovery criteria, established by the U.S. Fish and Wildlife Service (USFWS), include specific benchmarks for population size, the distribution of females with cubs, and mortality rates. Despite meeting or exceeding these criteria, attempts to delist the GYE population in 2007 and 2017 were overturned in court, so Yellowstone grizzlies remain listed as threatened under the ESA.
Key Influences on Grizzly Numbers
Several factors influence grizzly bear population dynamics in Yellowstone. Food availability plays a significant role, with dietary components including whitebark pine nuts, cutthroat trout, elk, bison, army cutworm moths, and various plants and berries. The decline of some traditional high-calorie foods, particularly whitebark pine due to climate change-induced beetle infestations and blister rust, and cutthroat trout populations, can lead bears to seek alternative food sources.
Habitat availability and connectivity are also important, as bears require large ranges. The occupied range of grizzlies in the GYE expanded threefold between 1990 and 2022. However, this expansion has recently slowed or even retracted in some peripheral areas, often due to increased human presence. Human-bear conflicts, such as vehicle collisions and management removals, pose a consistent threat and are the primary cause of grizzly mortality. These conflicts often intensify when natural food sources are scarce, leading bears closer to human activity.
Ongoing Conservation and Management
The continued health of the Yellowstone grizzly bear population relies on collaborative conservation and management efforts. The Interagency Grizzly Bear Committee (IGBC) coordinates these efforts, bringing together federal agencies like the National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, and U.S. Geological Survey, and state wildlife agencies and tribal nations. This interagency cooperation is fundamental to implementing the Grizzly Bear Recovery Plan.
Management strategies include public education programs focused on bear safety and proper food storage, which are essential for minimizing human-bear conflicts. Habitat protection and restoration are also ongoing, involving the establishment of bear management areas with seasonal closures, the installation of bear-proof food storage containers in campgrounds, and the restoration of fragmented habitats. These adaptive management approaches aim to ensure the long-term viability of the grizzly population, promoting coexistence between bears and humans across the Greater Yellowstone Ecosystem.