Elk in Northern Yellowstone herd older than average

By SCOTT McMILLION, Chronicle Staff Writer

LIVINGSTON -- The northern Yellowstone National Park elk herd isn't just getting smaller, it's getting a lot older, too.

"The northern herd is fast becoming a geriatric elk population," said Tom Lemke, a biologist here for the Montana Department of Fish, Wildlife and Parks.

The average age of elk harvested during last winter's late hunt at Gardiner hit a record high: 8.2 years for cows and 9.1 years for bulls.

Ten years ago, the average was 6.2 years and 5.9 years, respectively.

Statewide, the average elk is 4 or 5 years old.

Since 1996, Lemke and assistants have been pulling teeth from elk killed in the annual Gardiner late hunt. Those teeth have then been measured, like tree rings, to get an accurate age for each animal.

"It's beyond anything we've seen before," Lemke said Friday. "It's incredible to have 50 percent of the animals be 9 years old or older."

A geriatric elk herd could be especially vulnerable to extreme winter weather, he said. Very young and very old elk are generally the first to die in those conditions.

And the advanced age of the elk could make it hard for the herd to recover from the declines of the past several years.

The average age of the herd is increasing "because there are fewer young animals to replace the older animals," Lemke said.

For the past four years, biologists conducting annual surveys have found between 12 and 14 calves per 100 cows in annual spring surveys. That ratio is known as the "recruitment rate" and is a critical number for wildlife managers.

"For its overall health and vitality, we know calf recruitment needs to increase in order to see the age structure of the herd return closer to the norm," Lemke said.

The northern Yellowstone elk herd -- which migrates between the park and parts of Montana -- has been studied intensely for decades, but has come under increasing scrutiny since 1995, when wolves were reintroduced to the park.

Although numbers have fluctuated greatly over the decades, since 1995 the overall size has declined steadily from about 19,000 to about 9,500.

Many have been quick to blame wolves, but other factors are at play.

A new study has shown that 70 percent to 75 percent of radio-tagged elk calves die in their first year, mostly in the jaws of predators -- 55 percent to 60 percent were killed by grizzly and black bears, 10 percent to15 percent by coyotes and the remainder by wolves.

Another recent study says that hunting by humans, combined with the drought, could be a major reason for the decline.

"Climate and harvest rate are justified explanations for most of the elk decline," said the study by Doug Smith and Daniel Stabler, of Yellowstone's Center for Resources, and John Vucetich, of Michigan Tech University.

That study, published in the scientific journal Oikos, noted that although the region hasn't seen much winter for years, dry summers have reduced the availability and quality of food.

The study also found that wolves tend to take very young or very old elk, while human hunters harvest many prime animals. The authors created mathematical models that found that elk killed by wolves likely were mostly "compensatory" deaths, meaning they probably would have died anyway.

FWP maintains that wolf kills are highly "additive," meaning many of those animals would have survived without the wolves on the ground.

Lemke said Smith's models "are honest differences of opinion and interpretations and use of the data."

Proof will come in future years, now that the number of human hunters in the area has been drasticly reduced. The Gardiner late hunt, for example, peaked in 2000 with 2,880 permits. When the hunt resumes next month, only 100 hunters will have permits.

If hunting was a major factor in the herd's size, there should be changes coming in the age structure and size of the herd, Lemke said.

But the fact remains that, whatever the cause, the herd is old, and potentially vulnerable.

"The aging of the northern Yellowstone elk herd is an additional factor that could make it more difficult for this herd to expand," Lemke said.

Scott McMillion is at scottm@dailychronicle.com

Reader Comments