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 (bit.ly/1XHm8Mz).
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.
Daniel Thompson, large carnivore section specialist for the Wyoming Game and Fish Department, said it's not unusual for management removals to climb and then recede.
He pointed to 2010 as another busy year for biologists. That year, 15 bears were killed for repeated offenses, one was killed accidentally while being handled and six live bears were removed from the population. Eighteen other grizzlies were killed that year by hunters, homeowners or maliciously.
"We have a high year like this, then it quiets down," Thompson said.
Another reason for an increase in management removals is that there are simply more bears crowded into a confined area. Since bears need large home ranges and are territorial, young, old and female bears will often move to the fringes of prime habitat to avoid fights with large, dominant males.
"Grizzly bears are moving into areas outside the recovery zone," van Manen said. "They are getting into more and more of those areas where the potential for conflicts are greater."
The Greater Yellowstone Ecosystem includes Yellowstone National Park and mountainous national forests in Montana, Wyoming and Idaho that border the park. The region encompasses about 9,200 square miles. Inside that boundary, the grizzly bear population was estimated last year at about 760 bears, which van Manen said is known to be an underestimate.
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