Black bears are a significant and expanding wildlife presence in New Jersey. This article explores the typical timing and nature of their winter dormancy, along with factors influencing their activity.
General Hibernation Timeline
Black bears in New Jersey generally begin denning in late fall or early winter, between late October and December, preparing for a period of reduced activity. Pregnant females typically den first, often as early as the last week of October. Other bears, including males and non-pregnant females, usually follow suit by December. They commonly emerge from their dens in the spring, typically between March and April. This timeframe is a general guideline; exact timing can vary.
Influences on Hibernation Timing
Several environmental and biological factors influence when New Jersey bears enter and exit their dens. Food availability plays a significant role; a scarcity of natural food sources, like acorns and other nuts, encourages earlier denning. Conversely, abundant human-provided food, such as garbage or bird feeder contents, can delay denning or shorten dormancy. Mild winter temperatures also contribute to later denning or earlier emergence, enabling bears to remain active longer. The bear’s physiological state, particularly pregnancy, also dictates den entry.
What Happens During Hibernation
During their winter dormancy, black bears in New Jersey enter a state known as torpor, which differs from the deep hibernation seen in some smaller mammals. While in torpor, their metabolic rate, heart rate, and breathing significantly slow down. Heart rate can drop from 40-50 beats per minute to as low as 8-10 beats per minute. Their body temperature also decreases slightly, typically remaining above 88 degrees Fahrenheit, allowing them to awaken relatively quickly if disturbed.
Bears do not eat, drink, urinate, or defecate during this period, relying entirely on stored fat reserves. Remarkably, they can reabsorb waste products like urea, recycling nitrogen to maintain muscle and bone mass. Den sites are often secluded, including hollow trees, rock cavities, brush piles, or even ground nests, providing insulation and security.
Exceptions to Full Hibernation
Not all black bears in New Jersey undergo a full, uninterrupted period of torpor. Mild winter conditions can lead some bears to remain active or to emerge briefly for food. Easy access to human-associated food sources, such as garbage and bird feeders, incentivizes bears to stay active rather than denning. Male and non-pregnant females are more likely to have shorter or interrupted dormancy than pregnant females, who remain in dens to give birth in January. This adaptability allows survival where consistent food or warmer temperatures reduce the need for prolonged denning.