ELI5: Why do animals hibernate?

Animals hibernate to save energy and survive the winter when it is too cold outside and there is not enough food to eat.

Think of your body like a smartphone. When you are running around, playing games, and using apps, the battery drains very quickly. But if you are far away from a charger and your battery is running low, you can switch your phone to low-power mode. In this mode, the screen dims, background apps close, and the battery lasts much longer.

Hibernation is just an animal putting its body into the ultimate low-power mode.

During spring and summer, the world is like a giant, open grocery store for animals. There are plenty of berries, nuts, insects, and plants to eat. But when winter arrives:

• Snow covers the ground, hiding plants and seeds.
• Cold weather makes insects disappear.
• Finding a meal takes a lot of hard work and uses up too much body heat.

Once an animal enters hibernation, amazing changes happen to stretch that stored energy across several months:

• Their heartbeat slows down to just a few beats per minute.
• Their breathing becomes very slow and shallow.
• Their body temperature drops so they do not waste heat trying to stay warm.