Cookie had been up at the nest earlier in the morning but looked weak, according to Friends of Big Bear Valley, the nonprofit that runs the Big Bear eagle nest cam. The chick was hardly breathing and not moving much, the group said.
FOX40 sister station KTLA reports it died at around 8 a.m., according to the U.S. Forest Service. The survival rate for bald eagles in their first year is just 50%, the agency noted.
A camera has been streaming from the nest since Cookie's mother, Jackie, laid two eggs in March. The eggs hatched in April, and a contest to name the new eaglets was held.
A group of kindergartners in Santa Ana won with the name "Cookie," while a third grader from Rancho Cucamonga came up with "Simba."
Initially, both chicks appeared healthy. Then wintry weather brought snow to Southern California's mountains.
Temperatures dropped to 26 degrees on Sunday as a late-season storm brought a couple of inches of snow to the area, the U.S. Forest Service said. Hypothermia likely caused Cookie's death, a doctor told Friends of Big Bear Valley.
The nonprofit said with Big Bear's elevation, eggs should ideally be laid in April. Eggs laid in January, February and March get exposed to more inclement weather.
Days before Cookie's death, the nest cam captured Jackie trying to keep her eaglets warm as snow fell at Big Bear Lake.
"This last storm was a tough one with rain first and then snow and cold temperatures (just like last year)," the nonprofit wrote on Facebook. "As we could see with Jackie, the feathers got wet and then the snow stuck to them. The chicks weren't able to fit fully underneath her yesterday and last night."
Another eaglet died at the same nest in Big Bear this time in 2018, the U.S. Forest Service said.
"The chicks at this age are too big to be both fully covered during brooding, and since their juvenile contour and flight feathers are not fully grown yet, it is hard for them to retain body heat if the downing feathers get wet," the agency tweeted. "Rain followed by snow is never a good combination, as it begins to ice the body. The mother was observed this morning having a hard time shaking it off this morning."
The significant snowfall has forced Big Bear Mountain Resort to hold operations until Friday.
Cookie's body will likely be moved off to the side or buried by new nesting material, Friends of Big Bear Valley said. As of Monday, its sibling, Simba, appeared to be up and moving.
A slight chance of showers and thunderstorms are in the forecast for the area on Wednesday and Thursday.
"We are mourning with all the rest of you," the group said. "Nature can be very tough... We will all be rooting for Simba to stay strong and healthy."