Discover the Reason Grizzly Bears Are Causing Parts of Yellowstone National Park to Close

Written by Jennifer Geer
Updated: August 27, 2023
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Grizzly bears are causing parts of Yellowstone National Park to close. The National Park Service (NPS) is warning visitors that certain sections of Yellowstone National Park will be closed this fall because biologists will be conducting a research survey on grizzly bears in the area.

Scientists are monitoring the bear population in Yellowstone as part of the Endangered Species Act. To do so, biologists with the Interagency Grizzly Bear Study Team (IGBST) capture the bears. The scientists are then able to study the bears and collect data by collaring them.

The field captures will happen between August 28th through October 31st. Visitors to the park should watch out for the posted warning signs for closed areas and avoid all areas where the signs are posted.

“Monitoring of grizzly bear distribution and other activities are vital to the ongoing recovery of grizzly bears in the Greater Yellowstone Ecosystem,” The NPS explained in a written statement. “In order to attract bears, biologists use natural food sources such as fresh road-killed deer and elk.”

How Many Grizzly Bears Live in Yellowstone National Park?

Young Grizzly bear crossing road in Yellowstone National Park, Wyoming

In 1975, only 136 grizzly bears lived in Yellowstone National Park. Today, the number is up to approximately 1,000.

©Don Mammoser/

According to the NPS, an estimated 1,000 grizzly bears currently live in the Greater Yellowstone Ecosystem. This is an increase from only the 136 bears that lived there in 1975. Around 150 to 200 of the 1,000 bears have their home range either entirely or partially within the park.

How Many Grizzly Bears Live in North America?

Grizzly bear with cubs

Biologists capture and radio monitor grizzly bears in the wild to keep track of bear populations.

© Cooper

Grizzly bears are an endangered species, although they are making a comeback. There are an estimated 55,000 grizzly bears in North America, with the majority (30,000) living in Alaska.

It’s estimated the grizzly bear population dropped to only around 600 to 800 in the 1960s. In 1975, the bears were listed as threatened under the U.S. Endangered Species Act. Since that time, recovery and conservation efforts have boosted the grizzly bear population in Alaska and the lower 48 contiguous states.

How Does Capturing the Bears Help Biologists Study Them?

IGBST monitors the Yellowstone bear population by radio-monitoring a portion of them. By observing the bears, biologists can document things such as average litter sizes, cub survival, and how often female grizzly bears are birthing cubs. When monitoring these activities, biologists gather enough information to allow them to estimate population size. 

How Big Do Grizzly Bears Get?

Closeup of Large Grizzly Bear

Male grizzly bears can weigh up to 900 pounds.

©Jacqui Martin/

Grizzly bears are massive animals and they require a very large home range (up to 600 square miles.) The females are smaller, weighing up to 300 to 400 pounds. But the males can grow very large, up to 900 pounds, and eight feet tall.

The photo featured at the top of this post is © Steve Boice/

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About the Author

Jennifer Geer is a writer at A-Z Animals where her primary focus is on animals, news topics, travel, and weather. Jennifer holds a Master's Degree from the University of Tulsa, and she has been researching and writing about news topics and animals for over four years. A resident of Illinois, Jennifer enjoys hiking, gardening, and caring for her three pugs.

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