It's a typical January day: the temperature plummeting, the wind gusting, snow clouds gathering. A perfect day for a swim -- if you happen to be a polar bear or a California sea lion in residence at the National Zoo.

One polar bear swims while another frolics in the waterfall, picking up dead leaves. And all the sea lions -- including a baby born in June -- cavort in their unheated pool.

"They love winter," says collection manager Elizabeth Frank, taking a visitor on a tour of the winter zoo, where the most striking seasonal difference is the smaller number of human visitors.

"The camels and the bears love it, too. They grow thick coats. In summer they shed so much that we get complaints from the public that they look sick."

The two-humped Bactrian camels, wearing luxuriant 100 percent camel-hair coats, were stripping bark from a piece of tree, pausing occasionally to huddle together, one of them resting its head on the other's neck. Two spectacled bears also seemed to be giving each other bear hugs, but most of the bears were in their dens. Hibernating?

"They don't den up," says Frank. "But they slow down and sleep a lot and they eat less."

Most of the other animals get more to eat in winter but lose weight anyway, according to Frank.

"It's cyclical," she says.

If heavier meals and heavier bedding (in this case, more hay) sound familiar to humans trying to get through the winter themselves, the similarities don't stop there. Like humans, the zoo animals also tend to spend more time indoors.

Flamingos, for example, spend the whole winter indoors -- in a Florida-style house with an indoor pool and a wall-to-wall picture window overlooking their summertime yard and its now-empty pool. The tigers plunge into their pool in all temperatures but, like the lions, they're taken inside in the late afternoon if the nighttime temperature is expected to fall below freezing. The monkeys, who normally exercise free choice about whether to go out or stay in, are also locked in on sub-freezing nights.

"In the case of group animals, there's always a chance a dominant one might chase another outside and not let it in again," explains Lisa Stevens, collection manager for monkeys and apes. Stevens keeps the gorillas and orangutans inside the ape house if the temperature goes below 50o F, although one of the residents objects.

"That male orang -- we call him Junior but his real name is Atjeh -- will poke you and get you to follow him to the chute that leads to the play area outdoors," says Stevens.

The pandas, whose keepers are putting in a new floor during the winter lull, get to go outdoors more during the cold months. The only time they're not allowed out is in summer when the temperature goes above 70o F. Two winter mornings a week they're put in the same outdoor yard to prepare them for another breeding attempt this spring.

Frank says you can tell the male panda from the female because the black of his hindquarters extends only to the top of his legs while hers comes up over the hips.

"He wears the socks and she wears the pantyhose," she comments.

Some animals stay outdoors in winter but have indoor amenities brought to them. The owls get heat lamps in their nesting boxes and the ducks on their pond have three- sided clear plastic lean-to shelters, also with heat lamps. Two black swans, however, had shunned the shelters and were taking turns sitting on their outdoor nest in what is obviously not the normal nesting season.

"They're from Australia, and they haven't changed their light cycle," explains Frank. "This is summer to them." LIONS AND OTHERS IN WINTER: The zoo's a fine and quiet place in winter, but there are things going on. In a program this Sunday called "Walk, Trot and Gallop," the Archaesus Mimes will show visitors how to move like animals. Other free Sunday afternoon programs, all from 1 to 3 in the education building, include: January 23, elephant education; January 30, zoo photography; February 6, things that go bump in the night (animal phobias); February 13, bird music; February 20, monkeys, apes and us; February 27, puppet-making; March 6, art in the park.