When a burst water pipe signaled the arrival of spring, Sofia, 25, and Yulia, 20—the only two bears at the Korkeasaari Zoo in Helsinki—woke from hibernation. It was a day in February, but they didn’t care much about the Gregorian calendar.

The mother and daughter began hibernation in mid-November, but the warm early winter made their rest intermittent until the severe frost settled them into their shared den, an unusual behavior for them.

When temperatures dropped below freezing inside they huddled together. As it warmed, a leaking water pipe woke them but their den stayed dry so they continue to use it.

“This winter the bears didn’t sleep for long periods,” said keeper Susan Nuurtila in a news release sent to Finland Today. “They often stretched or peeked outside before returning to rest and we gave them light food.”

Now awake, the bears explore their snowy enclosure daily, scratching on trees, rolling in snow and sniffing around but still spend most of the day resting.

Keepers provide light snacks like salad and fruit alongside some dry food; as appetite returns they’ll switch to a diet of vegetables, grains, meat and fish.

Recent mild winters have shortened the bears’ continuous hibernation periods. This year’s longest was only three weeks.

Korkeasaari Zoo can cool dens to aid sleep during mild winters but nothing is as effective as true freezing weather.