Here's a breakdown:
* Black bears: Typically hibernate for 4-7 months, from late autumn to early spring.
* Brown bears: Hibernate for 4-6 months, with some individuals hibernating for as long as 8 months.
* Polar bears: While they don't technically hibernate, they enter a period of denning for 4-8 months during the winter.
It's important to note that bears are not truly "sleeping" during hibernation. Their body temperature, heart rate, and breathing slow down significantly, but they can awaken briefly to adjust their position or shift to a new den.