Unlikely But True: Mountain Climber Grizzlies

Photo credit: Jeremy Vessey on unsplash

We’re starting a periodic series focusing on what you probably didn’t know about
greater Yellowstone ecosystem wildlife. This is part 1.

Grizzly bears are one of the biggest charms (though not if you get too close) of
Yellowstone and Teton National Parks. With good guidance and a decent amount of
luck, a traveler is totally capable of seeing one in the area.

You’ve learned a thing or two about grizzlies on this blog before, but today we’re
focusing on a surprising trait that was only relatively recently discovered.

For the past few decades there have been accounts of grizzlies traversing mountain
sides climbing up to 10000 ft (over 3000 m). Many biologists were originally quite
skeptical that this was even happening. Why would they expend the effort to get up
there? After all, surviving year to year is often significantly a matter of animals
performing some instinctive energy expenditure cost-benefit analysis (grizzlies
probably don’t use spreadsheets for this, in case you wondered).

Biologists watched what the grizzlies did at these high elevations, and it seemed to
include a lot of digging, shifting, and sifting of rocks. So, after waiting for the bears to
retreat somewhere else, the biologists moved in. Digging under the rocks in the area
where the bears had lingered, they found army cutworms, the caterpillar that is the
immature form of miller moths. As it happens, these cutworms have among the highest
body fat percentage of any animal.

The bears knew what they were doing. This would make the journey worth it. Many
people are used to thinking of fat as a bad thing, but it’s necessary to take in a certain
amount of fat to survive. For an animal that spends the winter in a den, having large
amounts of excess fat is important.

How did the bears know where to find the army cutworms? It’s hard to know for certain
but perhaps some bears were shown as cubs by their mothers where to find such
nutritious grubs. Or maybe the grizzlies could smell the cutworms, bears having an
excellent sense of smell. Either way, feeding on army cutworms could be exactly what it
takes for some grizzlies to survive when food is hard to come by.

This practice (though relatively rare) of grizzlies climbing mountains to find grubs can
inspire us both not to assume we know everything about the complex ecosystems
around us and how our actions will affect other species. We can also learn to exercise
extreme caution around animals that will do whatever it takes to survive.

This post is brought to you by Flat Creek Inn.