Small insects, big lessons

Every summer researchers fly the same routes at the same time of year to count grizzly bears at 53 moth sites in the Absaroka Mountains in the Greater Yellowstone Ecosystem. That’s right; moths. And this year the researchers noticed something different. They recorded 500 bear sightings.

Kelsey Dayton

From 2004 to 2011, researchers averaged about 200 to 250 bear sightings at the moth sites, said Dan Bjornlie, a large carnivore biologist with the Wyoming Game and Fish Department. (Those numbers are not individual bears because researchers often observe the same bears multiple times.)

But there was a significant increase in the number of actual bears seen at moth sites. Researchers say it’s likely due to a larger than normal moth population, but also due to last year’s low snowpack which melted early and opened up more moth habitat, Bjornlie said. The snow levels likely allowed easier travel for grizzlies to moth sites, too, he added.

Bjornlie said the data from this summer is important because it further demonstrates that grizzlies are generalist omnivores. It also shows they adapt to changes in food sources. “The more we learn about all the different things bears are eating — and we seem to find new things all the time — it just makes it more clear there a lot of different things bears can eat,” Bjornlie said. Which is important information as wildlife managers work toward delisting the animals.

Grizzly bears were delisted in the Yellowstone ecosystem in 2007, but the ruling was challenged in court. Opponents to delisting cited an inadequate conservation strategy and also noted the impact of the decline of white bark pine wasn’t considered in the delisting decision. In November 2011, the Ninth Circuit Court of Appeals ruled the strategy was fine but agreed with the need for more information on the grizzly’s reliance on white bark pine. Studying the impact of the tree’s decline, as well as other food sources, became a priority for wildlife managers.

The moths have a wing span of only up to about 2 inches, so bears have to eat tens of thousands of them, which they dig out from moss and under rocks. Despite the insect’s size, it has the highest caloric value of any documented food source for grizzlies in the ecosystem, according to Bjornlie. The moths provide 7.9 kilocalories per gram — more than animal carcasses, cutthroat trout and nearly twice as much as white bark pine seeds.

And grizzlies will tolerate each other’s company to feast on moths. In one area, researchers observed as many as nine beers feeding, and up to 23 bears in a larger area.

So far most moth sites attracting grizzly bears are in the Absaroka Mountains and nearby area, which provides good moth habitat with large expanses of alpine flowers in vast talus fields, Bjornlie said. There are moth sites in the Tetons and Wind River Mountains, too, but so far grizzly bears don’t seem to use the sites like they do in the Absaroka mountains, Bjornlie said.

The increase in moth consumption could also be attributed to a growing — and therefore expanding — bear population. The most recent population estimate is 608 bears in the ecosystem. With more bears in the ecosystem the animals are venturing into new areas for territory and perhaps discovering the other moth sites.

Half the bear observations this year were made in just three of the total 53 moth sites. Those three sites were on the eastern edge of the mountains in areas where bears didn’t frequent until the 1990s. This, too, is important data as more grizzly bears mean the animals will be moving to find food and space. “As bears move into new areas they find the food sources that are available to them,” Bjornlie said.

Banner photo by Paul J./Flickr.

— “Peaks to Plains” is a blog focusing on Wyoming’s outdoors and communities. Kelsey Dayton is a freelance writer based in Lander. She has been a journalist in Wyoming for seven years, reporting for the Jackson Hole News & Guide, Casper Star-Tribune and the Gillette News-Record. Contact Kelsey at

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Kelsey Dayton is a freelancer and the editor of Outdoors Unlimited, the magazine of the Outdoor Writers Association of America. She has worked as a reporter for the Gillette News-Record, Jackson Hole News&Guide...

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  1. I do not agree with these singular theories why there were so many more bear sightings at the moth smorgasbords up there in the Absaroka alpine.

    All of these notions are partially correct. The one that was left out of the article is the fact that the existing bear population is just plain hungrier all around. Another possible factor is more people haunting the mothsites to do the counting. The secret is out, lamentably so. I have to ask why we never hear about the full lifecycle of these Army cutworm moths, a/k/a the ” Millers” that seem to reside their entire lives in your closet or garage , but are actually mostly born in the Great Plains and migrate into the high country in late Spring , leaving only a relatively eggs and catepillars as they go . Ask anyone who lives on a main migration route how thick these critters can be. Biblical.

    Whatever is happening to moths in Kansas , eastern Colorado, and the rest of the Great Plains is a far greater determinant of that part of the moth’s life spent in the higher elevations of the Rockies; things like pesticide use and drought.

    Mothsites aside, presumed numbers of Absaroka non-Yellowstone grizzly are likely significantly overestimated anyway , for political reasons, due to some skewbald computer modeling being shaded by the desire of grizzly managers to see more bears ” on paper” so they can shove the agency-driven delisting process further along.

    Combining all these divergent data sets only reinforces my belief that we humans know much less about grizzlies and moths than we think we do , but bureaucrats have it built into their own ecology to effuse theories regardless, right or wrong or giddily off in the wheatfields…