Where do bears go when they hibernate? Cartoons convinced me they all lived in caves, but I'm not so sure.

Submitted by Forge_craft4000 t3_10krj74 in askscience

I think this is a science question because it's about a natural process. Seriously, where do bears go to hibernate? I'm assuming they instinctually go for safe places where they won't be bothered or affected by weather, and perhaps places that are relatively warm and solitary. I've been led by Hollywood to believe bears hibernate exclusively in caves, but I've lived in places with lots of bears and it's flat forest land as far as the eye can see (Florida). I know there are limestone cave systems, but they're far and few between in most places. I'm just wondering where else in the woods is a good, safe, warm, sheltered, protected, viable place for them to go to sleep for 6 months. Thickets? Fallen tree mounds? Do they dig holes for themselves?Unless they all crowd in together there just aren't enough caves for all of them! Where do the beers sleep???

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KnoWanUKnow2 t1_j5u7tht wrote

Largely, they hibernate in dens that they dig themselves. They'll use a ready-made cave and save themselves the digging, but typically they dig one themselves. They may return to the same den year after year.

Polar bears can't dig into the ground because of permafrost, so they dig into a snow mound and den in there.

Just do an image search of "bear den" and you'll see loads of pictures.

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IsaacQqch t1_j5urdez wrote

Wait, polar bear hibernate ???? The température don't change why hibernating ?

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MrWrock t1_j5usklc wrote

Temperature definitely changes but food source changes probably have more of an effect. Black bears on BC's Vancouver Island don't hibernate due to tear round food sources.

In fact, no bears truly hibernate. They wake up, stir around, stretch, and go out for food when the weather is nice. What they do is called torpor

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CFL_lightbulb t1_j5vgth7 wrote

This is neat, and I never knew this. Thanks for the facts!

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very_busy_newt t1_j5wle0d wrote

What is the difference between torpor and hibernation?

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djublonskopf t1_j6mlod3 wrote

True hibernation is a long-term period of dormancy...weeks, or even months of continuous metabolic slowdown. Going into and out of it takes hours. Very few animals actually hibernate—certain snakes, bees, and bats, as a few examples. They generally stay "asleep" for the entire period, perhaps waking up only rarely to relieve themselves.

Torpor, instead, is much more short-lived, and generally involuntary...when it's cold their metabolism slows down and they conk out, if it warms up they get up and stretch and move around, maybe go find a snack. A lot of "hibernating" animals really just experience torpor during cold nights for a season, but are still somewhat active most days.

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MadcapHaskap t1_j5utcg9 wrote

The Arctic is sunny all summer, and dark all winter. The temperature changes a ton, as do hunting conditions.

In Grise Fiord, for instance, the average high in July is 7⁰C, the average high in February is -27⁰C

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KnoWanUKnow2 t1_j5uutzb wrote

Only the pregnant female polar bears dens. Technically they don't hibernate, as their body temp does not fall and her heart rate does not drop. But she will stay in the den from around October until around May, not eating and not leaving, while she gives birth to her cubs and feeds them for the first few months.

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Limos42 t1_j5x82oi wrote

I can understand not eating, but what about drinking?

How do they not dehydrate just from breathing?

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KnoWanUKnow2 t1_j5ya81i wrote

She doesn't pee. Apparently her kidneys shut down and other processes are used to remove toxins from the blood without wasting water.

She doesn't sweat.

The only water she loses is from respiration. This quickly forms ice on the surface of her den, which solidifies and creates a physical barrier that hinders further moisture from leaving.

She's using her fat reserves, she'll emerge having lost 30% of her weight. Part of the biological process of breaking down fat into energy releases water. For instance, the equation for breaking down triglycerides is:

C^(55)H^(104)O^(6) + 78 O^(2) --> 55 CO^(2) + 52 H^(2)O + energy

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cookerg t1_j5uy8zl wrote

It definitely changes. Google "tundra" for arctic summer and winter landscape scenes.

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Alittlebitmorbid t1_j5vd26u wrote

"Planet Earth" has shown a mother polar bear hibernating. She gave birth in her den, nourishing the little ones until they are big enough to follow and withstand the cold. She does not leave until then and is really famished. And you see her rolling around in the snow to clean herself.

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earthwormjim91 t1_j5u6v5q wrote

They go wherever they can. A lot of time that is digging a den under tree roots or something.

Another key fact is that bears don't actually truly hibernate. They go into what is called "torpor". It's a similar state with lowered metabolism, heart rate, breathing, etc. Except, they aren't fully sleeping that whole time. They do frequently get up, move around, forage for food, drink water, etc.

https://academic.oup.com/bioscience/article/70/2/129/5661110

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amaurea t1_j5u8lyg wrote

>Another key fact is that bears don't actually truly hibernate. They go into what is called "torpor".

Your reference doesn't seem to support this? Also, Wikipedia says:

>Historically it was unclear whether or not bears truly hibernate, since they experience only a modest decline in body temperature (3–5 °C) compared with the much larger decreases (often 32 °C or more) seen in other hibernators. Many researchers thought that their deep sleep was not comparable with true, deep hibernation, but this theory was refuted by research in 2011 on captive black bears and again in 2016 in a study on brown bears.

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earthwormjim91 t1_j5ubuxp wrote

The linked studies in that section don't directly support what the article states.

The study in captive black bears controlled for things like access to food and water. Researchers completely removed access to food and water to trigger hibernation and the end of hibernation in the bears to monitor them.

The study on wild brown bears found that they were very susceptible to disturbance and would move dens during the winter if disturbed, so not in a total hibernation. It also directly calls out the black bear study as having hibernation artificially started and ended and not representative of the wild.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750243/

>In a previous study, the HR in captive black bears was reported to decline gradually over five weeks from the date that food and water were removed [45]. Our finding that changes in Tb began long before changes in HR suggests that studies on captive bears with an artificially defined end of the food/water season might not represent the actual sequence of events in the wild.

They concluded that hibernation is driven by environmental factors rather than the physiological factors that the black bear study concluded, and that periods of warming can drive them out of their dens or delay hibernation.

They also highlighted the need for differentiating between small mammal hibernation and bear hibernation because of these.

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amaurea t1_j5ul8ug wrote

That's all true, but that doesn't mean bears don't hibernate. All these articles call it hibernation.

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Megustamyn t1_j5v2adc wrote

They go wherever they can. They've been known to go into crawl spaces under people's homes.

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BuffaloBoyHowdy t1_j5vi2t8 wrote

There was a case in New Jersey where a black bear chose to winter in a small garage built into the side of a hill. When it was discovered, the authorities suggested it be left alone so as not harm it. The garage wasn't used for a car, just storage, so no big deal.
I've also read that bears do NOT reuse their dens for at least several years. And they typically don't use dens made by other bears.

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