Biologists Finally Found What's Hunting Grizzlies in Yellowstone — And It Shouldn't Be Possible

A Rising Tide of Grizzly Deaths00:00:00

The Greater Yellowstone Ecosystem saw a record 74 grizzly bear deaths in 2025. While human activity has historically been the leading cause, researchers are now grappling with a surge in natural mortality that cannot be easily explained by previous models.

The Paradox of Protected Populations00:02:24

Surprisingly, cub survival rates are significantly lower in protected areas like the interior of Yellowstone compared to areas near human development. This indicates that the safest terrain for bears is not necessarily the safest from other, more dominant grizzly bears.

Sexually Selected Infanticide00:03:31

Biologists have confirmed instances of sexually selected infanticide, where large males kill the offspring of females to induce breeding receptivity. This practice, along with aggressive territorial behavior, has become a major natural cause of death for both cubs and smaller adults.

Ecological Pressures and Future Outlook00:06:53

The rise in natural deaths is attributed to three main factors: the population reaching its ecological carrying capacity, the loss of essential food sources like whitebark pine seeds and cutthroat trout, and the natural behavior of male grizzlies becoming more observable due to increased monitoring. The future of the grizzly population remains uncertain as they adapt to a changing environment.