This is a busy month for the region's black bears, the beginning of the fattening-up season during which they will stuff themselves silly to build up reserves that will carry them through the winter. They may gain two pounds a day and double their weight within the next three months.

"They have an excellent sense of smell, which helps them find food," said Karina Blizzard, associate director of wildlife and heritage for the Maryland Department of Natural Resources. "They are feeding nonstop starting in September."

Acorns and nuts are their first choice, but they will eat anything: grubs, insects, carrion, small live animals, bird food and garbage.

"If it's been a really good year -- there are lots of acorns on the ground for them -- they are not going to need to move around much," Blizzard said, adding that bears roam perhaps a couple of square miles from home. But if the acorn crop is poor, "you are much more likely to see them moving around, hitting crops hard, getting into trash cans and interacting with people more than we'd like to see."

A wet spring often foretells a good acorn crop, and Blizzard is optimistic that the bears will be busy enough with what's on the ground that they won't look for what's on people's back porches. But she urges residents of areas with established bear populations to mind their bird feeders and trash cans, especially until bears den up for the winter.

This is not the most likely time to see a black bear in the Washington area. There are breeding populations in the farther reaches of the region, Maryland's Frederick County and the Blue Ridge Mountain jurisdictions in Virginia. It is in the spring -- when adolescent bears (born early the previous year) are kicked out of the family because mother wants to breed -- that young bears may wander into more developed communities.

Young black bears have a fair amount in common with the giant panda cub born in July at the National Zoo. (Thanks to DNA evidence, experts now put giant pandas in the bear category.) Like him, black bears are born helpless, with no fur to keep them warm and with their eyes closed. They typically weigh eight ounces, which is double what newborn pandas weigh, but still mighty small.

Pandas, black bears and other bear species have cubs that "are much smaller than what would be expected based on the size of their mothers," wrote David L. Garshelis, author of one chapter in "Giant Pandas: Biology and Conservation," published last year by the University of California Press. One possible explanation is that ancient bears hibernated and, without access to food, could not support development of a fetus. Young bears at birth are less far along in their development than human babies.

Today's bears are not true hibernators. For up to six months, black bears go into winter dormancy, during which their body temperatures lower and they do not eat or drink, but they can be roused from sleep. In the wild, giant panda mothers fast for only two or three weeks and change dens frequently in the winter, which makes them different from other bears.

Some black bears, especially pregnant females, will go into their winter dens as early as Halloween. The last ones in, generally males, may wait until late December or even early January. In mild winters, when lots of food is available, some may not den up at all.

A den may be as simple as a pile of brush or a hollow tree, although Blizzard said, "They will take the Marriott suite of a rock den if they can get it." Their fur insulates them enough that they do not need protection from the cold.

Male black bears are usually the first to emerge in spring. Females with cubs are the last to wake. By mid-April, black bears are out in the world again.

-- D'Vera Cohn