Rest with the marmots, rise with the bears

To hibernate, perchance to dream

How well would you sleep after a 30,000-calorie dinner?

We all know that black bears hibernate all winter, and that means you won't ever see them when you're out in the snow, right? The correct answer might surprise you, according to the Department of Fish and Game's bear expert and Yosemite rangers.

To make sure there's no confusion about whom we're discussing, black bears are the only bears that live in California today. They are of the species Ursus americanus and come in many colors from blond to cinnamon to dark brown to black.

Winter hibernation is all about food or, more correctly, a lack of it. When food becomes scarce, black bears typically relocate to the cold side (the north side) of the mountain, look for a place with solitude - they frequently build their dens under a large log - and then pretty much shut down until conditions are more favorable. But it's not uncommon for them occasionally to come out and urinate, or even to wander about for a while for no apparent reason, according to Fish and Game wildlife biologist Doug Updike.

In addition, if there's enough food available or if a bear didn't put on enough weight before beginning its "nap", you may occasionally find one wandering around looking for food, as Yosemite rangers found one in the middle of last winter at Tuolumne Meadows. In places where ample garbage or food is available all winter - as around Lake Tahoe and Mammoth Lakes - black bears may stop hibernating altogether.

The length of hibernation varies with latitude and elevation, with bears that live further north or higher up having longer periods of lethargy. In the Sierra, the average bear will be in its den from approximately January to mid-March, and upon leaving, Updike explains, it will immediately head for the warmer south slopes in search of the season's first sprouts.

Bears are not "true hibernators" because they only lower their body temperature by approximately 12° (from about 100° to 88°), whereas smaller mammals like bats, chipmunks, squirrels, and marmots bring their temperatures down to 35° - 40°.

In case you wonder why black bears don't need to lower their temperature as much, it's because they are able to store more energy internally relative to their rate of energy use than smaller mammals. In the fall, in preparation for hibernation, black bears go through a phase of hyperphagia (increased eating), consuming 20,000 to 30,000 calories a day. Their large mass and fur also help retain body heat, and while hibernating they are able to cut their metabolic rate in half.

Unlike humans, who tend to lose muscle mass quickly when sedentary (most of us notice a difference when we're inactive for just a few weeks), black bears are able to conserve much of their strength over the winter, as well as to regenerate and repair their bones while dozing. Scientists are intrigued by both these capabilities and are studying them in the hope of finding therapeutic applications for patients who are confined to bed, as well as for astronauts, who lose both muscle mass and bone while in flight.

The true hibernators, and cold-adapted small animals that stay out all winter long, rely on "brown fat" a tissue that most mammals, including humans, have as newborns but lose shortly after being born. Brown fat cells contain a high density of mitochondria, which produce heat, whereas white fat cells have comparatively few mitochondria and serve primarily as storage sites for energy. The brown fat cells provide the energy that's needed for a real hibernator to be aroused.

Like the bears, even the true hibernators are not continuously dormant; all of them periodically awaken. Marmots are the largest true hibernator, and our local species, yellow-bellied marmots, can hibernate from as early as September or October to April or early May, but they awaken every week or so throughout their period of torpor, not for feeding but maybe for urinating.

Snowcampers may be wondering, "What does this information about bears mean for those of us who are out there winter-camping?" Frankly, it's difficult to get a definitive answer.

No one wants to go on the record saying that bears are never a problem, because it is possible that they could be. But according to Updike, it would be rare for a camp to be ransacked at higher elevations during January and February, possibly through mid-March, and that's certainly the experience of the Bay Chapter's Snowcamping Section. In more than 35 years of leading training trips every winter, no one recalls hearing about any incidents with bears, and most of the group's trips take place at elevations above 7,000 feet.

In case you encounter animal tracks this winter, coyotes, bobcats, white-tailed hares, and Douglas pine squirrels (also referred to as chickarees) are among the more likely animals to be active in areas with deep snow. Keep in mind that tracks made in softer surfaces can be deceptively large, particularly in light, fluffy snow.

If you're interested in learning more about how different animals and plants survive in harsh winter conditions, the Snowcamping Section's Alumni Group is leading a winter ecology trip the weekend of Jan. 19 - 21. You do have to be a "graduate" of the Snowcamping Training Series to qualify. If you're not, sign up for the Training Series this winter and plan on doing the trip next year; we hope to make it an annual outing. For more information, log on to www.snowcamping.org

or contact Marilyn Smulyan at mhsbike -at- sbcglobal.net or (415) 648-4062.

Marilyn Hope Smulyan