Your heart races and you gasp for air. Is it because you just ran a couple of miles on a soggy, uneven trail or because you just spooked a brown bear?
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In Alaska, bears add an element of risk to outdoor activities from birding or berry-picking to hiking, fishing and hunting. Some activities are riskier than others.
Trail running in bear country can be especially dangerous.
Biologist Stephen Herrero, author of "Bear Attacks: Their Causes and Avoidance" was one of the first to sound a warning in 1985 as trail running was becoming more popular and mountain-biking was coming into its own.
"These activities, which are characterized by speed, not cautious attention to the possibility of encountering a bear, increase chances of sudden encounters and related injuries," Herrero wrote.
Not only have bears nailed trail runners; they've injured runners on logging roads and lightly traveled roads on the edge of suburbia.
Yet fear is no reason to turn into a couch potato. You can take common-sense precautions to avoid trouble. You can prepare and rehearse for a worst-case scenario.
Typically, the problem for runners is not that a bear will spot you jogging through the woods and give chase like a cat after a mouse, but that you'll surprise a nearby bear.
The do's and don'ts of trail running
Carry EPA-approved bear pepper spray.
Avoid seasonal food sources such as berries and salmon streams.
Make noise when appropriate.
Wear headphones and zone out
Run at dawn or dusk
Brown bears, not black bears, are the main issue.
If you suddenly encroach on the personal space of a black bear and force it to "fight or flee," it will almost always flee. Even if a black bear does make a rush at you, it will usually stop short of making contact if you just stand still.
Black bears are not mini brown bears.
When Herrero and Brigham Young University professor Tom Smith analyzed "A Century of Bear-Human Conflict in Alaska," they found the top reason for confrontation was surprise.
You don't want to intrude on the personal space of a brown bear and force it to make that quick fight-or-flight decision. And a brown bear's "personal space" is pretty big. It means a lot more than getting between a sow and her cubs.
Most bear-related injuries result from people startling a brown bear at a distance of 55 yards or less.
Here are some suggestions for avoiding sudden confrontations:
Don't run at dawn or dusk, when bears tend to be active. Bears prefer to be out and about during the day, but the more human activity there is during the day, the more bears resort to nocturnal feeding and high activity levels at dawn and dusk.
Think about bear food along the trail you're using. Is it near a salmon stream? In spring and early summer, avoid calving areas for moose, along with vegetation like horsetail, sedge, and skunk cabbage. In late summer, think berries.
Don't wear headphones and zone out. Instead, pay attention and make noise when appropriate. You don't have to whoop and holler every step of the way, but when you see that the trail ahead of you has limited visibility, give a shout. Herrero and Smith found that of 118 bear-related injures and fatalities in Alaska, 83 occurred in areas with "poor visibility."
Run with a partner and stick close together. You'll make more noise. You'll have an extra set of eyes and ears looking for bears. If you do startle a brown bear, there's safety in numbers - provided you're close enough together so the bear sees two people, not one.
Herrero and Smith note that single hikers are much more at risk of a bear encounter than any other group.
"It seems that bears size up the odds before engaging, and if it is one-on-one they appear much more likely to mix it up with a person than otherwise," they wrote.
Be extra cautious in fall. Bears are generally very alert; they detect us before we detect them, and then avoid us. But when bears go into a feeding frenzy in the fall - hyperphagia - they're not always as alert. They get really engrossed in feeding. They're less likely to avoid you simply because they don't notice you in the first place.
Rick Sinnott, Anchorage-area biologist with the Alaska Department of Fish and Game, points out that some runners make "puffing and wheezing noises, accompanied by feet slapping on the ground. These aren't the best noises to make in bear country - an injured or wounded ungulate might make similar noises."
It's highly unusual for a bear to spot a runner in the woods and give chase, but it has happened in the Anchorage area. Sinnott says most reports he has of bears chasing runners have been in spring during moose calving season.
"What I think is happening is that newly independent bears develop a search image for 'large animal running through the woods,' which is often a cow moose with one or more calves. So they learn to give chase. When a runner goes by ..."
Carry EPA-approved bear pepper spray, which weighs all of 8.1 ounces. When trail running, carry your bear pepper spray in hand, in a hip holster, or in an outside pocket of your fanny pack where you can quickly grab it.
Bear bells? Bears can't always hear them, nor do they always associate the dingaling sound with people. But bear bells are better than nothing, especially if you don't take the trouble to pay attention to your surroundings.
Dave Smith is the author of "Alaska's Mammals" (Alaska Northwest Books, 1995), "Backcountry Bear Basics" (The Mountaineers Books, 1997, 2006), and "Don't Get Eaten" (The Mountaineers Books, 2003). He lived in Glacier Bay National Park in the mid-80s and in Anchorage until 1997. He now resides in sunny California.