Happy Birthday, Black Bears!

by Mary Thill | Nature and Environment

Today, January 15, is a special day in the black bear calendar. It’s the mean and median of all black bear birthdays, according to a man who peeked into 122 dens over several decades to calculate this very thing.

So out there in the woods today, unseen to us in caves and hollows left by uprooted trees, a lot of 12-ounce baby bears are likely being born.

Gary Alt conducted the largest black bear study ever, from 1974 to 2000. As part of the effort, starting around Christmas, he would stick his head into the dens of female bears he fitted with radio collars over the summer in northeastern Pennsylvania. Then he listened for the sound of babies.

The earliest birth he observed was January 1, the latest January 27. There have been no similarly detailed studies anywhere else, but Alt thinks the range of dates probably applies as well in the Adirondacks as it does in Pennsylvania.

“I literally walked over a thousand miles to answer the question when are the cubs born,” he said by phone last week. “And I walked it in the coldest month of the year, through snow and through blizzards.”

Alt worked for the Pennsylvania Game Commission from 1977 to 2004. Now he’s a private environmental consultant living in California, and he’s still one of the world’s leading authorities on black bears.

Black bears mate from May to September, Alt says. The mothers go to den anytime from mid October to late December, depending on snowfall and the availability of food.

“I literally watched two different females mating 100 days apart . . . and they both gave birth on the same day,” he says. “How can this be? First of all, these cubs are tiny at birth. They’re only about 12 ounces. And how come they’re all born at the same time when they are breeding for such an extended period of time?”

Bears are delayed implanters, he explains. No matter when eggs are fertilized, they implant in late November or early December, a process triggered by the declining hours of sunlight per day. The developmental period is six weeks.

The cubs born this month will stay in the den and nurse for the rest of the winter. Their fur will grow longer and their eyes will open. They’ll emerge from the den with their mothers around April to begin learning to forage.

Most mothers will stay with their cubs throughout the summer and into the next winter, with some exceptions based on the age of the mother and availability of food.

Alt made many observations, including size of litter correlating to size of the mother, but most of those findings are specific to northeastern Pennsylvania, where food is abundant and bears grow exceptionally large.

To learn more about Alt’s black bear research, watch the four-part series “Lord of the Bears” on YouTube.

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