In Massachusetts, black bears mate between June and mid-July. Depending on food availability and snow cover, bears will den between early November and mid-December and exit between early March and mid-April. Pregnant females will always enter a den, as this is where they give birth. If food sources (such as bird feeders) are available throughout the winter, males, lone females that are not pregnant, and females with yearlings may be active during the winter.
Each winter, MassWildlife biologists visit the dens of female black bears (sows) with radio tracking collars. Sows may be in the den alone, with newborn cubs, or with yearling cubs born the previous winter. Newborn cubs are born small, blind, and helpless in the den in January. In order to give the mother a chance to bond with her cubs and for the cubs to grow, MassWildlife waits until the end of February before visiting dens of sows with newborns. Cubs born in the den this winter will stay with their mother all year and den again with her next winter, before dispersing as yearlings in April or May of the following spring. By immobilizing females and their yearling cubs, biologists collect important information on cub survival and growth after their first year.
Biologists locate the dens using telemetry equipment to listen for the female’s radio-collar signal. Winter dens may be a hollow log, rock crevice, or a ground nest under fallen trees or brush. Once the den is located, trained biologists immobilize the sow and examine the health of the bears. Information like body condition and weight are recorded, and newborn and yearling cubs are sexed and counted. The sow’s radio-collar is evaluated for proper fit and replaced if necessary. By radio collaring sows, biologists learn about survival and reproductive rates. This information enables biologists to model whether the bear population in Massachusetts is growing, declining, or stable. GPS-tracking collars, which record a location every 45 minutes, provide biologists with important information about black bear habitat use and movements, and how bears are using increasingly human-dominated landscapes.
Based on the survival and reproductive rates of females and the survival of their offspring, the bear population in Massachusetts is continuing to grow. Reports of bear sightings and nuisance complaints indicate that bear densities are increasing in central Massachusetts and the occupied bear range is moving east of I-495. This means that more of the human population in Massachusetts needs to learn how to coexist with black bears. You can help keep bears healthy and wild by not allowing bears to have access to food around your home or business. Removing bird feeders, securing garbage and compost, feeding pets inside, and securing beehives and chicken coops with electric fencing are just some ways to prevent conflicts with black bears. Bears that feed at bird feeders are being taught to look for food around people’s homes and in neighborhoods. This causes bears to spend more time in these places which can be a potentially dangerous situation for both people and the bears. Learn more: mass.gov/bears.
Please click here to see more video footage of black bear winter den research.