Feast mode ⏩ Sleep mode. Fat Bear Week is almost over. Wild grizzly bears will soon go into hibernation — a “winter sleep” that causes lower metabolism, slower heart rates and lower body temperatures. Even though our grizzly siblings Huck and Finley don’t hibernate here at the Zoo, they still experience seasonal diet changes that ensure they store enough energy for a long lazy winter. Brown bears, including grizzlies, are found in fairly healthy numbers worldwide, but many still face threats in