Bears Cubed: Virginia Tech Studies Three Bears, And Three Bears, And Three More Bears

April 28, 1998

(Blacksburg, Va, April 28, 1998) -- Three sets of triplets were born this winter to mama bears denned in the safely tucked away bear barn on Virginia Tech's Blacksburg campus. Lead researcher Mike Vaughan says that's a little more than customary but not highly unusual. Two cubs are the average litter.

He and his graduate students have been studying the life and growth patterns of black bears for 18 years. The College of Forestry and Wildlife Resources researchers participate with the Cooperative Alleghany Bear Study (CABS) in partnership with the Virginia Department of Game and Inland Fisheries.

In the summer when the game department rounds up nuisance bears, it gives six to Vaughan so he can study what happens to bears during denning, cubbing, and after birth. After the spring gobbler season, the mamas and cubs, who by then weigh about 12 pounds, are released back into the wilds of Virginia.

The bears are tattooed on their gums with an ID number, and some are tagged on the ears, so data can be recorded and studied in later tracking. Annual growth rings on teeth can reveal the age of adult bears. A bear first breeds when she is two and half to three and a half years old.

Some of the bears in Virginia that are being studied have been fitted with radio collars or a device that is inserted under their skin in the back. If the bear dies, a signal is sent and researchers are able to find the animal and try to determine the cause of death.

Vaughan and his associates estimate there are at least 4,000 bears in the commonwealth. Hunters take about 500 annually, which accounts for most of the mortality.

Vaughan's continuous studies have resulted in some amazing findings. "Bears breed between June and August with the peak of breeding in July," the wildlife professor explains. "The embryo, however, develops only to about 300 cells in the blastocyst stage. It floats and remains unattached in the uterus until early December."

"We don't fully understand the relationship between denning and the timing of implantation," the bear expert notes. "Our bears appear to implant before denning but in the wild that may vary from year to year."

Gestation is a short 60 days, and cubs are born in February while the sow is in hibernation. The cubs nurse every 30 to 40 minutes, while the mother continues to sleep.

Vaughan tracks this process with blood tests. Like other mammals, their plasma progesterone levels rise until implantation, then steadily drop until birth. The big question facing the researchers is what triggers implantation to take place in early winter?

The Virginia Tech researchers measure and weigh the cubs every 10 days. At birth they weigh about a half pound. But if you were to hold one, you would find it much stronger than a puppy dog.

Chris Ryan, wildlife graduate student, uses a five-foot-long blowgun to send some anesthesia into the mother's leg muscle to put the sow to sleep before entering the cage-den. Each mother has her own den.

Vaughan has also found that if the mother has had a lean food year and is unable to lactate, the cubs starve soon after birth and she consumes them to regain some protein. "What would you think is the only evidence left of this process?" Vaughan asks. "The tiny claws are the only parts that she does not digest and that get passed through her intestines."

"Black bears are one of nature's few real hibernators," Vaughan points out. "That is, they do not eat, drink, urinate, or defecate for three to five months while denning. What is so incredible is that their heart rate and body temperature drop only slightly. And they are not in a deep sleep -- they can be up instantly.

Rule number one when trekking in the wilderness: never come between a sow and her cubs. Rule number two: if you encounter a bear and see or hear the mouth "popping," slowly back out of sight and move on.

Dr. Vaughan's homepage is http://www.fw.vt.edu/fisheries/VAUGHAN
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Virginia Tech

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