Between Sleeping & Waking: Female Black Bears in Wintertime

“Ever since I was young, the story about bears was always the same. Bears hibernated all winter long, usually in a cave and would emerge in the spring. I have since learned a bit more about the environment and ecology and have found that there is much more to the story,” said State Parks staff member Patty Wakefield-Brown.

Hibernation occurs when an animal’s body temperature drops and its breathing and heart rate slows, thus lowering the metabolism of the animal, and conserving the animal’s energy. Bears are not “true” hibernators. They sleep for long periods of time but are easily awakened and, if the winter is mild, bears may wake to eat.   This behavior is termed torpor, a state or inactivity achieved primarily by a greatly lowered (reduced) body temperature for hours, days or months. Only woodchucks, jumping mice, and cave bats are the “true” mammal hibernators in New York State.

Taking a long winter nap when food is scarce and weather is bad is a great adaptation for bears. While in a state of torpor, a bear will not urinate or defecate in the den.  Their bodies absorb the urea and turn it into protein, which is needed during the long winter months.

During hibernation, female bears (sows) give birth and nurse their cubs.  Females have delayed implantation, meaning that the egg is not implanted in the uterus unless the female bear has the energy, weight, or does not have the physical requirements to provide for the cubs during pregnancy and just after birth, the egg is released and there is no pregnancy. That is amazing.  While in the den, sows wake up in January or February to give birth, generally 2-3 cubs. Black bear cubs are born altricial, which means helpless, hairless, and blind. Cubs remain with the mother for a year and a half or more before they disperse or she forces them out.

Bears generally emerge from their dens in late March and early April and are primarily interested in two things; eating and reproducing.  Mating occurs in May or June.  Males and females are sexually mature at around four years of age.

With the human population increasing and more and more land being transformed to accommodate this increase, the natural habitat of the American Black Bear is being minimized. Because of this, there is a greater likelihood that a person will have an encounter with a black bear. Wildlife biologists collar and collect data from bears to learn about their populations, home range, health and preferences for den sites. Like all wildlife that we share our environments with, keeping track of this data helps to create local and regional management plans.

Collecting Data on Sows and Cubs

“While a college student, I took a two- semester black bear management class. We worked with the New York State Department of Environmental Conservation (DEC) to assist in the creation of a database regarding den site criteria. We were able to accompany DEC staff on bear den visits in mid-March and collect data about the bears. The bears were outfitted with telemetry collars which enabled them to be found when they were in their dens during the winter months,” noted Patty Wakefield-Brown.

‘Photo 1’ below shows the DEC staff gently removing the tranquilized bear from the den; the entrance was on quite a steep slope.

Photo 1 resize in Publisher
Photo 1, by Patty Wakefield-Brown.

The bear was a female that had been previously collared. The purpose of the den visit was to change collars and to collect data including weight, visual appearance, take blood samples and note whether any cubs are present.  DEC staff also inspected the den, described its location, (i.e. old log, brush/thicket, hillside, under porch, etc.),  took measurements of the den’s  interior, what materials den was comprised of, and the amount of cover,  and noted the den’s proximity to humans, houses, and roads.

“On this day there were three cubs in the den with the sow.  As the mom was being ‘processed’ we got to hold the cubs to determine their age.  The way to age young cubs was to measure the hair on the tops of their heads (between their ears) or inside their ears, from the tragus to the tip of the ear (Photo 2) (Bridges et al. 2002).  When all the data was collected, the mom was placed back into the den comfortably with her cubs (Photo 3)” recalled Patty Wakefield-Brown.

Photo 4
Photo 3, by Patty Wakefield-Brown.

When bears disperse, they sometimes wander into populated areas creating human-bear conflicts. That was the case in October 2010, when a young male bear wander onto the Rochester Institute for Technology campus in Henrietta. The DEC natural resource managers ‘captured’ the bear and took him to a facility to collect data on him before he was relocated (Photo 4). The bear management class was invited to observe the event.   After the bear was tranquilized, a patch was put over the bear’s eyes, so that they don’t dry out (the bears don’t blink when anesthetized).  Blood samples were taken, ears were are tagged and a tooth was taken to age the bear, also the inside of the lip was ‘tattooed’ with a number and a radio collar was placed on the bear (Photo 5).The process was done very methodically and quickly. The bear was then released into the Hi-Tor Wilderness Area.

Winter slumbering bears are an essential part of the the ecosystems found in New York State parks.  They are part of the splendor of the natural world that mesmerizes us and holds us captive in its magic.  If you are lucky, you might get a chance to capture some of that magic if you see a bear in a New York State Park next summer.

Post and photos by Patty Wakefield-Brown, OPRHP.

Reference:

Bridges, A.S., Olfenbuttel, C Vaughan, M.R. (2002). A Mixed Regression Model to Estimate Neonatal Black Bear Cub Age . Wildlife Society Bulletin, Vol. 30, No. 4.

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