# How a Bear Survives Winter

How a black bear's heart, breathing and body temperature slow down in its winter den, and how it runs on stored fat until spring\.

By cal

Topic: Nature & Biology

[Open the interactive Jig](https://ask.jig.com/j/mqEV5hthaJeP)

## Transcript

### 1. Asleep under the snow

Deep inside a snowy hillside, a black bear is sleeping through the winter\. For months it will not eat, drink or even pee\. Let's look into its den and see how its body slows down to make it through\.

Drag the scene to look around the den from any side\.

### 2. A feast before winter

In autumn, food is everywhere, so a bear eats almost all day: berries, nuts and acorns\. It builds a thick layer of body fat\. That fat is the fuel it will live on all winter\.

### 3. A snug den

When the snow comes, the bear curls up in a den: a hollow under roots, rocks or a fallen tree\. It lines the floor with leaves and grass\. Snow piles on top like a thick blanket that keeps out the wind\.

A den is often barely bigger than the bear itself\.

### 4. A heart in slow motion

An active bear's heart beats about 55 times a minute\. In hibernation it slows to as few as 8 or 9 beats a minute\. Some beats are up to 20 seconds apart\! Switch between the two and watch the heart\.

### 5. Long, slow breaths

Breathing slows too: just one breath every 15 to 45 seconds\. Watch the lungs fill\. The heart beats a little faster while the bear breathes in, then slows right down in the long pause after\.

Here the bear takes one breath every 15 seconds\.

### 6. Warm, but not too warm

A sleeping bear's body only cools a few degrees, from about 37 °C to around 31 to 35 °C\. Staying warm means it can wake fast if danger comes\. Turn on the heat view to see the warm bear in its cold den\.

Ground squirrels and bats cool almost to freezing instead\.

### 7. Running on fat

The bear's metabolism, the body's way of turning food into energy, drops to about a quarter of normal\. It slowly burns its fat, which even gives it water\. By spring it may lose 15 to 30 percent of its weight\.

It turns waste into new protein, so its muscles and bones stay strong\.

### 8. Waking in spring

When spring arrives, the bear wakes up thinner and very hungry\. Its body can take up to three weeks to speed back up\. Scientists study bears to learn how to keep people's bones and muscles strong\.