It's cold and dark in Alaska, and most bears are now hibernating. But Bert and Ernie, two brown bear cubs at the Alaska Zoo, appear to have insomnia and are showing no sign of winter sleepiness.

Hoping to help them get some sleep, zoo caretakers stopped feeding the cubs this week, working on the premise that food availability, along with the cold and darkness, is a factor in determining when a wild animal hibernates.But another factor may involve learning. Biologists believe mama bears play a role in teaching cubs to hibernate.

The two Alaska Zoo cubs are orphans whose mother was shot and killed over the summer during her bold search for food on the porch of an Anchorage house. The cubs became zoo residents but may be returned to the wild in spring.

So far, however, the new zoo denizens show little interest in a den made for them and seem intent on staying up to play past their winter bedtime - with no mother to put them to bed for the winter.

"We can't actually teach them to hibernate," zoo curator Wayne Ray said Thursday. "They're exploring the den but so far haven't shown much inclination to use it. They're real alert and inquisitive."

Other zoo bears sacked out at the beginning of November. The bears may emerge from their dens occasionally, but they also may sleep through the long, dark Alaska winter.

"We've had quite a bit of subzero weather," Ray said but noted the fat furry 11-month-old cubs aren't chilled by the cold. Daylight is down to about seven hours and dropping.

Roger Smith, a state Department of Fish and Game biologist on Kodiak Island, a haven for brown bears, said hibernation is partly instinctive, brought on by decreasing daylight, the onset of severe weather and lack of food. But mother bears teach their cubs how and where to dig dens and go in with them for winter.

Although most orphans do not survive in the wild, some do, proving that they have figured out how to hibernate, state bear biologist Sterling Miller said.

"Intelligent animals like bears have an instinctive component and a learning component" that tells them what to do when winter comes, Miller said. Although scientists have studied what triggers hibernation, separating behavior into what is instinctive and what is learned would be difficult, he said.