I heard the first bear was spotted at Yellowstone! Does the length or severity of the winter change the hibernation length, especially for bears?

Answered by Gregg Losinski – ESER Education Specialist and Human/Bear Conflict Expert

Hibernation is a fascinating adaptation that many animals use to survive when harsh extremes are part of their environment. We think of hibernation in relation to cold, but there is a parallel process called estivation that occurs during very hot temperatures and allows animals like Idaho’s ground squirrel to survive. The important thing about either process is that the animals involved instinctively know that a big change is coming and prepare their bodies to deal with it.

When it comes to hibernation and bears the answer to this question is not as clear-cut as our friend the groundhog, who is closely related to our Idaho marmots. They are what we call a true hibernator. When they enter their winter burrows their body’s temperature and heart rate drop very low and they don’t wake up until springtime. They usually have a certain amount of fat in reserve so that in the case of the groundhog and their shadow, they can stay in their burrow if winter hangs on for six more weeks.

Bears are what some people call super-hibernators. They are different from the true hibernators because they are able to deal with winter in real time. Since hibernation is a function of saving energy, bears that have plenty to eat don’t need to hibernate. Female bears that are pregnant generally enter the dens earlier as a way to save energy need to grow their cubs. Males that have had plenty to eat and that are still able to access food can stay active later or even stay up all winter! Black bears in the southern US often remain active year round because food is so available.

Because captive bears must be supplied food to survive, places like Bear World allow bears to do what comes naturally and decrease food as fall progresses. That way the bears hibernate and it is less costly to maintain them. Just up the highway in West Yellowstone, Montana, the bears of the Grizzly & Wolf Discovery Center stay active all winter long. They are able to do this because the Center has a constant flow of food and are able to afford to feed all year long.
Even in the wild, grizzlies don’t always follow the “normal” hibernation rules. They can sometimes get up to stretch their legs and take a little stroll in the middle of winter. One thing that they don’t do when they wake up is to eat, drink, or go to the bathroom. The adaptations that all animals have to survive are truly amazing.

Hibernation Triggers

The instinct to hibernate varies among different animals. For some a drop in temperature tells them it is time to hibernate. Other animals notice a dwindling in the supply of food. And still others have a sort of internal calendar that tells them to hibernate around the same time every year. Finally, some animals can tell by the diminishing of daylight that it is time to hibernate.

Follow the Sun for a Day

Day length changes as the Earth revolves around the Sun. In this experiment, we will create a simple model of the Earth and sun and use it to explore the sun’s apparent movement across the sky.
Materials: Clear 2-quart bowl, large sheet of white paper, sharp pencil, erasable marker, compass

  1. Make an X in the center of the paper to represent our Earth.
  2. Take the materials outside. Find a level surface for the paper. Make sure the location receives sunlight all day.
  3. Place the bowl upside down on the paper. It represents our atmosphere. Mark an X on the center of the bottom of the bowl with the erasable marker and line it up with the X on the paper. Trace the edge of the bowl onto the paper to make it easier to line up.
  4. Mark North on the paper and the bowl.
  5. Each hour, touch the side of the clear bowl with the tip of the pencil so the shadow of the pencil’s tip falls on the X on the paper. Make a dot on the bowl on that spot with the marker.
  6. After each marking, predict the next dot will be. Which direction does the sun appear to be moving?

Note: To get accurate results, the bowl must sit in the same location and be lined up in the same way for each hourly reading.

The Earth rotates counterclockwise, toward the east. The sun appears to move west, but that it is the Earth’s rotation toward the east that causes this phenomenon.

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