Wildlife managers have euthanized 24 grizzly bears in the Greater Yellowstone Ecosystem so far this year, the highest number in the past five years.
Most of the bears, which are a protected species under federal law, had killed livestock or had become habituated to human food sources, according to information posted on the Interagency Grizzly Bear Study Team's website.
There's no one specific reason for this year's increase, which comes after two years of relatively few grizzly bear euthanizations, said Frank van Manen, supervisory wildlife biologist and leader of the team.
But factors that influence the situation include a larger population of bears pushing to the fringes of its core recovery area and a reduction in the availability of natural food sources.
This year has seen relatively low whitebark pine cone production, van Manen said.
The seeds of the cones are a great protein source found at high elevations, keeping bears away from more populated rural areas. In addition, it was a poor fall berry crop for chokecherries, another bear staple.
"It's clear that a number of valuable food resources are in low supply this year," van Manen told The Billings Gazette.
Thirteen of the bears, the majority of them adult males captured in Wyoming, were euthanized for preying on livestock. That's out of a known 47 grizzly bears that have been killed or removed from the ecosystem in 2015. The other causes of death range from intraspecies killings by other bears to collisions with vehicles.
In the past five years, including 2015, a total of 72 grizzly bears have been euthanized by managers in the Greater Yellowstone Ecosystem after they killed cattle, destroyed property or became a nuisance by seeking food at homes and ranches. Just over half were removed for killing cattle and sheep.
The 72 bears accounted for about one-third of all grizzly bear deaths in the ecosystem between 2011 and 2015.