Lots of animals hibernate. Hedgehogs hunker down, dormice curl up in a ball, and bats take to their roosts. Hibernation occurs when animals enter a state of almost total inactivity during the winter months.
They do this by slowing their heart rate, lowering their body temperature, breathing more slowly and reducing their metabolism. This helps them to conserve energy and survive for long periods of time without eating.
As with so many things, however, it’s a question of degree. Some animals rouse themselves from hibernation for a quick snack and a toilet break, before returning to their bed. Dormice do this and so do bats and chipmunks. This helps the animals to keep their strength up and get rid of any waste that would otherwise soil their ‘bed’.
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Bears, on the other hand, truly commit to hibernation. If you’ve never come across ‘Fat Bear Week’, check it out. Prior to hibernation, bears eat so much they can double their body weight. During Fat Bear Week, online spectators vote for the biggest chub-ster. (The 2025 award went to a 500kg brown bear called Chunk, who triumphed despite having a broken jaw.)
Unaware of this kerfuffle, the bears then get on with the serious business of settling in their dens and drifting off. The metabolism of the black bear slows by half, and its heart rate drops from 55 beats per minute to just nine. Bears do not enter a deep, continuous sleep, but remain in a state of ‘torpor’ where their body temperature drops by a relatively small amount, and they retain the ability to wake up quickly if they need to. This hibernation-like state can last for around six months, during which time they don’t pee or poop. At all.
Hibernating bears still produce urine, but they don’t expel it. Instead, any urine is absorbed back through the bladder into the body, where urea in the urine is used to build proteins. This helps the animals to maintain their muscle mass and avoid the build-up of toxic waste products.
Meanwhile, undigested solids accumulate in the large intestine, where any remaining water is also absorbed back into the body. This leads to the formation of a dry, solid, chunky poo which blocks the only available exit. The ‘faecal plug’ sits in the rectum until spring. Then, when the bears finally wake up, they do indeed poop in the woods.
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