Voting in Katmai National Park’s famed Fat Bear Week was underway Wednesday after a bear killed one of this year’s competitors and delayed the bracket reveal by a day.

Bear #469 attacked and killed bear #402 on Monday morning at Brooks River in the Alaska park, the National Park Service said in a release, pushing Monday’s bracket reveal to Tuesday.

The attack and the subsequent killing were captured live on webcams that have been set up in the park to follow the bears all summer. The nonprofit organization explore.org, which hosts and broadcasts the bear livestreams, held a live conversation Monday to discuss the attack.

It was not immediately clear what prompted the incident.

“National parks like Katmai protect not only the wonders of nature, but also the harsh realities,” spokesperson Matt Johnson said in the park service release. “Each bear seen on the webcams is competing with others to survive.”

Bear #469 was not included in the bracket, released Tuesday.

How Fat Bear Week works

Fat Bear Week, which the park service calls “an annual celebration of success,” puts 12 bears in the Alaskan Peninsula to the test before they head into hibernation for the winter.

Voting takes place over seven days, culminating in Fat Bear Tuesday, when one bear is crowned the fattest of the season.

“People may vote using any criteria they see fit,” the National Park Service said. “In the end, one bear will reign supreme.”

Explore.org encourages voters to “vote for the bear you believe best exemplifies fatness and success in brown bears.”

“Fat equals survival” for bears, who head into their dens for months without any food and could lose up to one-third of their body weight during that time, the park service said. Surviving hibernation means bulking up on a year’s worth of salmon and other snacks in only six months.

Large male brown bears can weigh up to 1,500 pounds in coastal areas or up to 500 pounds in interior areas, according to the Alaska Department of Fish and Game, and they can be 30% to 50% larger than female brown bears.

They weigh the least when they leave hibernation in the spring and can increase their weight by more than 50% by the time they re-enter the den in the fall.

The fat bears of 2024

This year’s contest pits eight bears against one another in the first round of the single-elimination bracket. Voting began Wednesday and will continue Thursday.

Four more bears earned a bye to the second round of voting Friday and Saturday.

In round one, Bear #909 Jr., who won this year’s junior contest, bested Bear #519, a female recently independent from her family. Bear #909 Jr. will now try to beat Bear #128, also known as Grazer, a mother bear who holds last year’s Fat Bear title.

Grazer is described as one of the “most formidable, successful, and adaptable bears” at Brooks River, according to the park service. In July, both of her cubs were “swept over Brooks Falls” toward Bear #32, also known as Chunk, who attacked and injured one of them before Grazer could come to their rescue.

The injured cub died later, and the surviving cub competed in Fat Bear Junior 2024, according to the park service.

Chunk, who the park service said is the “most dominant bear on the Brooks River,” has a bye and will face the winner of the Thursday matchup between Bear #856, a very large adult male who is one of the biggest on the river, and Bear #504, a mother bear and newcomer to the competition.

In another round one faceoff, Bear #903, a smaller male and another Fat Bear Week newbie, beat Bear #909, the mother of the junior contest’s winner. He will go head-to-head with Bear #747, a two-time Fat Bear Week victor so large he was named after an airplane and was once estimated to weigh 1,400 pounds.

The final round one matchup is between Bear #151, a large adult male nicknamed Walker” and Bear #901, a female who returned to the river alone after her first litter of cubs did not survive. The winner will move on to round two to meet Bear #164, a male who has grown a lot in the last few years, now appearing about as tall and as long as Bear #747.

Voting concludes Tuesday, and the fattest bear will be declared the winner.

This article was originally published on NBCNews.com