Bears: The Super Sleepers

Guest Poster and Wildlife biologist Daryl Ratajczak explains why bears are extra hungry this time of year, so we can all take care with our garbage, pet food, and birdseed to help keep bears wild!

As I write this blog, bears across North America are in the midst of hyperphagia. That’s a nerdy techy-term biologists use to describe the insane feeding binge bears are on while trying to pack on the pounds in preparation for their long winter’s sleep.

Though I have written blogs about their feeding behaviors and their favorite foods (Acornology 101), I have yet to describe their most amazing adaptive feature of all…hibernation.

Hibernation is a general term used to describe long periods of inactivity, sometimes due to extreme cold but mostly due to lack of food. To put it simply, animals decide to “sleep” through the winter since food resources are scarce or non-existent.

But given the fact that winter, especially in the northern climates, can last months on end, how can an animal survive the entire winter without eating or drinking? That, my friends, is the crux of this amazing adaptation. And bears do it better than any other animal.

Complex Biology Made Simple

Instead of starting by describing the life processes necessary for an animal to hibernate, let’s start by thinking about your car. Say you were to fill up your gas tank to run a test on fuel efficiency. In other words, what’s the optimum rate an engine needs to operate to stay running the longest?

The answer is pretty straightforward, the slower the engine operates, the longer it will take to burn the gas in the tank. For example, a car driving 70 mph down the highway is going to burn through its tank of gas faster than one idling in the driveway, sitting in the parked position.

And Voila’!!! You just learned everything you need to know about hibernation!

Much like a car, animals more-or-less have to put their bodies in “Park” to survive the winter on their respective tank of gas (fat reserves). Placing their bodies in “park” and idling through the winter, however, is what is truly interesting and amazing.

Photo Credit: National Park Service

Hibernating animals need to drastically reduce the amount of energy (gas) they expend. As most of you know, being active and exercising burns up a lot of energy. So the first thing an animal must do when entering hibernation is stopping moving, hence the “sleeping” part.

Here is the issue: All mammals, even when sleeping, must maintain a constant body temperature and continue to perform basic life functions. Things like breathing and maintaining a heartbeat to keep their blood pumping are just a few of the more important functions since it keeps them alive. Therefore, it takes a considerable amount of energy, even when sleeping, to maintain their basic bodily functions. And this is what makes a hibernator so special.

  • Hibernators almost completely shut off their bodily functions.
  • Their respiration rate drops to next to nothing.
  • Their heartbeat is barely detectable at only a beat or two per minute.
  • And their body temperature drops to just above freezing.

Their overall metabolism drops 50 percent for roughly every 20°F they lose in body temperature in more technological terms. This means they’re burning half the energy they would if they were only sleeping. When they go into complete “hibernation mode,” their bodies are literally in a frozen coma.

In this nearly frozen state, they barely expend any energy, but they’re also barely alive. In fact, it takes them quite a bit of time, possibly a day or so, to “wake up.” It’s kind of like trying to start a car that hasn’t been started in a long, long time. It may actually take a while to get it going.

Pretty neat, huh?

And then there are bears.

But wait a minute….aren’t bears hibernators?

Yes and no.

Bears hibernate… but they are not true-hibernators. They are what we call super-hibernators. Or, as I like to call them, “super sleepers.” Here’s why bears are so extremely special and a phenomenon in the animal world.

When bears hibernate…

Their breathing slows to only about a breath per minute.

Their heart may beat only about once every 20 seconds.

But this is where it gets interesting…

Their body temperature only drops a smidgen, from roughly 99°F to 92°F. Yet, with only this slight temperature drop, their metabolism has already decreased by 75 percent. They’re literally just sleeping but barely expending any energy in the process, and because their body temp is so high and close to normal, they can literally wake up in just a few minutes.

Photo by Pete Nuij on Unsplash

Crazy is the fact that although they are sleeping fairly close to how you and I would, they won’t need to eat, drink or poop for up to six months! I could barely make it through the night without doing one of those three!

Crazier still is that humans would die of toxicity from their kidneys not adequately filtering the waste products in their bloodstream if we tried going that long without removing the waste.

And craziest of all…bears barely lose any muscle mass. They primarily burn only fat. On the other hand, bedridden humans usually lose muscle and bone mass first if they stay in bed too long. Can you imagine going to sleep for a few months then waking up and all your fat is gone? I would be in heaven!

If the medical world could unlock the mysteries of bear hibernation, it could lead to amazing discoveries. Not only could they make huge strides in their fight against diabetes, but it could eventually lead to a weight loss system that actually works while you sleep. Imagine, all those gimmicky late-night weight-loss infomercials would go away. That alone would be the greatest benefit to society.

Alas, the medical community is still perplexed about how bears can do this, so we patiently wait in infomercial purgatory.

But now you see why bears are freaking amazing.

[Guest post by Daryl Ratajczak, black bear biologist, and advocate. Daryl is the former Black Bear Program Coordinator and Chief of Wildlife for the state of Tennessee. He is also a regular wildlife instructor for Wildlife for You]

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