Black bears in North Carolina undergo a period of winter dormancy to conserve energy when food is scarce. While often called hibernation, this state is more precisely termed “denning” or “winter lethargy.” This distinction is important because their physiological changes are not as extreme as those seen in true hibernators.
North Carolina’s Bears and Their Denning
The American black bear, North Carolina’s only bear species, exhibits a unique form of winter dormancy. Unlike deep hibernators, black bears do not experience a drastic drop in body temperature. Their body temperature typically decreases by only 10 to 15 degrees Fahrenheit, remaining between 88 and 98 degrees Fahrenheit, allowing them to be easily roused if disturbed.
During denning, a black bear’s heart rate significantly slows, dropping from an active 40-50 beats per minute to 8-19 beats per minute. This adaptation enables them to survive extended periods without food or water. They also do not need to wake periodically to eliminate waste, as their bodies efficiently recycle metabolic byproducts.
Timing of Denning in NC
Black bears in North Carolina typically begin denning in late fall to early winter, with entry into dens occurring from November through January. The exact timing can vary, influenced by regional differences and environmental conditions. For instance, some male bears in the coastal plain might remain active throughout the winter, depending on food availability.
Most black bears emerge from dens in late winter or early spring, typically March or early April. Some may exit as early as February, while females with newborn cubs might stay until late April. This variability reflects the individual bear’s condition and the specific demands of raising young.
Environmental Factors Influencing Denning
Environmental and physiological factors influence when black bears in North Carolina enter and emerge from dens. Food scarcity, such as a lack of acorns and berries, is a primary driver. Cooler temperatures and snow cover also contribute to the decision to den. Bears build fat reserves in autumn, essential for sustaining them through denning.
A bear’s reproductive status plays a significant role. Pregnant females typically enter dens earlier and remain longer than males or non-reproductive females, providing a secure environment for giving birth and nursing cubs. The availability of suitable den sites, like hollow logs or rock crevices, also influences denning.
Behavior During Denning
While denning, black bears maintain reduced metabolic activity. Their body temperature remains relatively high, allowing them to react quickly if disturbed. They do not consume food or water, relying on stored fat reserves. This period of inactivity is crucial for energy conservation during the lean winter months.
Females give birth to cubs in the den, typically between late December and early February. The newborn cubs are tiny, blind, and helpless, weighing less than a pound. The mother nurses them throughout the denning period, remaining until cubs are strong enough to follow her in spring. Bears utilize various den types, including hollow logs, rock crevices, brush piles, or excavations under fallen trees, sometimes making nests of leaves and grass inside.