Alaska's Chubby cub competition new to Fat Bear Week 2021

Bear 909 is a top contender for 2021's most cuddly cub. Photo / N. Boak, Park Service Photos, Supplied

If you go down to the woods today, you're in for a BIG surprise.

Fat Bear Week has arrived in the Katmai National Park in Alaska. This celebration of bears at their cuddliest has become an annual event for the US Park Service.

Fed by the run of salmon through the parks, bears have gorged themselves in preparation for a winter-long hibernation. Eating a half-year's worth of calories in a matter of months, the bears rely on fat reserves to see them through the lean season.

It is survival of the fattest.

From scrawny spring bears to gorged autumn grizzlies, the change in body weight is spectacular.

Fat bear of the year:747. Photo / N. Boak, Park Service Photos, Supplied

Since 2014 the service has posted weight gain photos of their bears for the public to vote for fat bear of the year. Possibly fed by the hunger for outside the 2020 competition saw 640,000 votes from around the world.

Crowned 2020's king of corpulence was bear 747. From images the animal's volume was estimated at a massive 634 litres of fuzz and fat.

"Bears arrive in July looking thin and frail. Now as winter approaches they are rotund and ready to retire into hibernation," says explore.org and competition founder Charlie Annenberg Weingarten.

"It is a true success story."

This year for the first time the Park has introduced a junior league for chubby cubs.

Yearlings, on their own for the first time, have their own competition. Concluding on Friday the little league is looking to crown their first Fat Cub of the Year 2021.

To be entered into the competition bears must have been recorded in the Brooks River Katmai National Park in early summer, with identified photos from both early and late summer.

The Heavy weight category begins next week on. September 29 and conclude on Fat Bear Tuesday, October 5.