The black bear population in Connecticut is growing and expanding its range, making sightings common in many neighborhoods. Residents often encounter these large mammals, whose annual cycle is dictated by the changing seasons and food availability. To survive winter scarcity, black bears enter a long period of dormancy, a biological adaptation that allows them to conserve energy until spring returns. Understanding the timing and biology of this winter rest is important for human-bear coexistence in the region.
Seasonal Timing of Den Entry and Exit
The typical calendar window for black bears to settle into their winter dens in Connecticut extends from late November through mid-March for the general population. This timing is not absolute, as the decision to den is heavily influenced by environmental and biological factors. A severe and early cold snap or a sudden lack of natural food sources can prompt bears to den earlier than usual.
Conversely, a milder winter or the availability of human-provided food, such as unsecured garbage or persistent bird feeders, can delay den entry or cause some bears to remain active for extended periods. The gender and reproductive status of the bear is a significant variable. Pregnant females, known as sows, are often the only bears that biologically need to den, as they give birth to their cubs in the den between late December and early January.
Sows enter their dens earlier than males or non-pregnant females and remain longer, often not emerging until late March or early April. This extended denning period ensures newborn cubs, which weigh only about 6 to 12 ounces at birth, have enough time to grow and develop before facing the external environment. The young cubs are dependent on their mother for protection and sustenance, and she will not leave the den until they are capable of following her.
Metabolic Changes During Winter Sleep
The winter dormancy of black bears is often incorrectly referred to as true hibernation, but it is more accurately described as a deep, prolonged state of torpor. This distinction is significant because, unlike true hibernators such as woodchucks, the bear’s body temperature remains relatively high. The body temperature of a torpid black bear drops only about 12 degrees Fahrenheit, a minimal reduction that allows the animal to be easily roused if disturbed.
During this period of rest, the bear’s metabolism is suppressed by as much as 75%, and its heart rate slows dramatically, sometimes dropping from a typical 40 to as low as 10 beats per minute. Torpid bears do not eat, drink, urinate, or defecate for the entire denning period.
Instead of excreting waste, the bear recycles the urea produced by its body, converting it back into usable protein. This process allows the bear to conserve water and maintain muscle mass throughout the four to six months it spends denned. The bear relies exclusively on the thick layer of fat reserves it accumulated in the fall, which provides the necessary energy to survive the winter and, for pregnant sows, to produce milk for their cubs.
The Crucial Periods of Preparation and Emergence
The period leading up to denning is marked by an intense biological drive known as hyperphagia, an urgency to consume massive amounts of calories. In the fall, a black bear’s primary focus is to build up the fat stores necessary to sustain it through the winter, often foraging for food up to 20 hours a day. During this power-eating marathon, a bear can consume up to 20,000 calories daily, which is roughly ten times its normal intake.
This intense feeding behavior is the time when bears are most likely to wander into residential areas in search of high-calorie foods like acorns, nuts, and berries. Easy access to human-associated food sources, such as garbage and bird feeders, provides maximum caloric reward for minimal effort, which increases the potential for the human-bear conflict. Residents must be diligent about securing all attractants during the fall months to prevent bears from becoming habituated to feeding near homes.
When bears emerge from their dens in the spring, they are driven by a powerful hunger and are actively seeking food to replenish their depleted energy reserves. The immediate post-emergence period is another time of high human-bear interaction, as natural food sources like spring vegetation and insects are still scarce. To protect both the bears and the community, it is advisable to remove all bird feeders from late March through November. Ensuring garbage is secured and not left out overnight is also a simple action that can prevent a newly emerged, hungry bear from lingering in a neighborhood.