Black bears give birth now!

January 30, 2010

While New Hampshire’s human population remains hunkered down indoors for the remaining weeks of winter, the State’s black bears have recently given birth in their winter dens.

Black bear cubs are born at the coldest time of year weighing only half a pound, hairless and with eyes closed. Female sows attend to cleaning, nursing and snuggling fast-growing newborn cubs. Twins and triplets are common. In late March when biologists will visit radio-collared bears in their dens, the ten week old cubs will be alert, fully-furred and weigh five pounds each.

Andy Timmins, the Bear Project Leader for the NH Fish and Game Department works closely with black bear researchers to maintain collared bears that contribute new data to ongoing studies which began with the need to retrieve data and maintain batteries in radio collared “nuisance bears” in Lincoln and in Berlin between 2000 to 2003. Visiting bears’ dens in late winter – particularly those with several yearling cubs - “can get pretty tricky” according to Timmins.

Since 2004, Fish and Game biologists have worked with bear researcher, Ben Killham in the Connecticut River Valley. Timmins says Killham currently has ten radio collars on related females this winter. The data collected during the annual winter den checks allows researchers to validate population models by verifying the health and reproductive rate of the State’s female black bears. “The den checks allow us to keep our finger on the pulse of what is actually happening out there” adds Timmins.

A common misconception is that black bears hibernate in winter. Bears enter a state of winter torpor with reduced heart rates and respiration rates during winter when food is scarce, but they are not inert. They are capable of becoming alert and even fleeing a den if threatened. Females with newborn cubs do not sleep as soundly as females with yearling cubs born last winter or solitary males.

Another misconception is that bears use dens year-round and that dens are located in caves. Bears create new dens each winter and rarely if ever re-use the same den in subsequent years. According to Timmins, that indicates there is no shortage of suitable sites. Dens are most often dug beneath tree roots, alongside fallen logs, in brush piles or in dense vegetation on the open forest floor including in dense thickets of saplings regenerating in open clearcut areas. Some bears simply lie down and wait for snow to cover them. Timmins says pregnant females don’t invest any more effort in choosing a den than males or females without cubs.

To reach the dens in March, a team of up to five or six people hike-in on snowshoes using a radio antenna which receives the very high frequency (VHF) signals emitted from radio collars on study bears. As radio signals grow stronger, biologists leave their helpers behind to await a radio call. Biologists walk in tighter and tighter circles after removing snowshoes and remaining very quiet – no talking - to avoid alarming bears inside a den. Biologists search for a mound of snow or tell-tale signs including broken vegetation and a frost hole where bear breathing keeps snow melted. Typically, biologists need to dig down in the snow to actually locate a bear. If they will be able to extract the adult bear to collect data and weigh it, it is temporarily sedated using a drug that takes effect in ten minutes or less. If they can’t reach a bear, they leave.

Once an adult sow is immobilized, helpers arrive to measure and weigh cubs and take bear hair samples for later DNA analysis to determine familial relationships. Helpers tuck bawling cubs into their coats to keep warm. According to Timmins, cubs typically fall asleep when firmly snuggled inside a coat. Biologists then cover the sow’s eyes to reduce stress and cut a pole to rig net attached to a scale to weigh her. They remove a small pre-molar tooth for laboratory analysis where a tooth cross section will reveal her age.

Nearly 800 other bear teeth are collected, coded and sent annually to the UNH lab from bears taken during the fall hunting season to establish a statewide bear population age profile. The mean age for males taken during the hunt is three to four years old. Females average six years old. Each year, a few bears are taken with ages in the teens. In captivity a black bear may reach 40 years old. In the wild, natural mortality typically occurs before age 20. Bears face many hazards including roadkill, hunting, food stress, social pressures from other bears and outright persecution by landowners.

The baseline biological date obtained from bears taken during the annual autumn hunting season is enriched by the data from winter den checks. The number of cubs per sow and adult weights and relative health of wintering bears helps NH Fish and Game biologists forecast the population health and determine management objectives for the following autumn. Biologists can then predict population outcomes under varying fall acorn crops and harvest levels. Den checks of sows with yearling cubs reveal first year survival rates. The GPS data stored in each collar also reveals den entry date and den departure dates.

Each den check can be accomplished efficiently in as little as an hour if all goes well. The team replaces bears in their den and reassembles materials removed from the entry before retreating.

I can’t help but imagine a bear re-awakening in April saying: “I had the strangest dream this winter…”

Naturalist Dave Anderson is Director of Education and Volunteer Services for The Society for the Protection of New Hampshire Forests. His column appears every other week in the New Hampshire Sunday News. E-mail him at or through the Forest Society's Web site: