El Niño warmth won't hamper black bears from denning this winter in the eastern United States, wildlife experts said. However, it may be causing some delays.
Above-normal temperatures set records in the eastern U.S. during fall and the early days of winter due to El Niño. The warm weather plays a role in keeping food supply available for hungry bears, which can cause some delays in hibernation.
"If there is an abundance of food, they tend to hibernate later," Pennsylvania Game Commission Press Secretary Travis Lau said. "But once finding food begins to cost them more calories than they get from eating, they will go down."
Also, the shorter period of daylight this time of year is usually the trigger for bears to den.
Pregnant females typically begin denning the earliest, Wildlife Biologist Larry Bifaro of the New York State Department of Environmental Conservation said.
"Females with young from  will stay together as a family group and are the next to den," Bifaro said, adding that this is important to provide shelter to the cubs. Males of various age are last to den.
The optimal winter from a bear's perspective provides an abundance of fall foods, especially beechnuts, which would also be available in the early spring when they leave hibernation.
"[Ideal winter conditions occur when] deep lasting snows come early and melt for good early in the spring," said Wildlife Biologist and Black Bear Project Leader Forrest Hammond of the Vermont Fish and Wildlife Department. "A good ‘nut year' the previous fall means that there would still be nuts available for them after the snow melts in the spring."
On the contrary, a poor winter would follow a fall with little available food.
"If the nuts were not available in large amounts the previous fall, then the bears have little to eat when they leave their dens in the spring," Hammond said. "During these types of years, many newborn cubs and sub-adults may die of malnutrition."
Also, late snows that last into the spring are not ideal, especially when most of winter is warm and wet. That can make denning conditions miserable for the bears, Hammond added.
The weather has already started to cooperate for a good denning season with snow falling in New England and downwind of the Great Lakes. Colder air also rushed in at the beginning of 2016 in the eastern half of the U.S.
Colder blasts will be punctuated by brief warmups for most of January, according to AccuWeather Chief Long-Range Meteorologist Paul Pastelok.
During mid-January, colder air will sweep eastward from the Central states, following one or two storms that can bring snow and ice to parts of the Ohio Valley, central Appalachians to New England, mainly away from the Atlantic coast, Pastelok said.
Some bears need extra help to survive their early years; that's where groups such as Appalachian Bear Rescue (ABR) of Townsend, Tennessee, help.
More than 17 cubs are overwintering at ABR and are not denning yet, ABR President Dana Dodd said. ABR cares for black bears that are orphaned, injured or in need of medical care.
"They may not den at all," Dodd said. "They are at ABR because they were orphaned and seriously underweight. They were far too small to survive a winter in a den."
"The last time that cubs overwintered with ABR was 2011-2012," Dodd explained. "The cubs do slow down as it gets later in the year. They might not come out to eat on a very cold day, but they will come out when it is warmer."
ABR, which celebrates its 20th anniversary in 2016, cared for 33 cubs in 2015 as the natural food supply failed in its area. The group has cared for bears from eight states and from national parks.