Bear check: Winter den inspections reveal healthy black bear population

  •  Massachusetts Division of Fisheries and Wildlife Connecticut River Valley District Biologist Dave Fuller prepares a collar for a tranquilized bear in Leeds.  MASSWILDLIFE

  • Massachusetts Division of Fisheries and Wildlife biologists Susan Ingalls, from left, Dave Fuller and Erik Amati collar a female bear in New Salem in March 2018. In top photo a sow with her cubs. PHOTOS COURTESY OF MASSWILDLIFE

  • A collared black bear lays on the ground next to radio telemetry equipment.  MASSWILDLIFE

  • A cub is weighed in Belchertown in February 2018.  MASSWILDLIFE

  • Massachusetts Division of Fisheries and Wildlife Connecticut River Valley District Biologist Dave Fuller works with a black bear on the Mount Holyoke Range in January 2018.  MASSWILDLIFE

  • Massachusetts Division of Fisheries and Wildlife Connecticut River Valley District Biologist Dave Fuller and MassWildlife Black Bear and Furbearer Project Leader Dave Wattles conduct research on radio-collared black bears at an unspecified location in the commonwealth.  MASSWILDLIFE

  • Cubs with sow in a den in March 2018.  MASSWILDLIFE

  • Massachusetts Division of Fisheries and Wildlife Central District Biologist Mike Morelly working with black bears in Petersham in February 2019.  MASSWILDLIFE

For the Gazette
Published: 4/12/2019 5:34:24 PM
Modified: 4/12/2019 5:34:14 PM

Have you spotted a black bear in your backyard this spring? Or maybe on the bike path? It can feel like a close encounter, but state wildlife biologists have been getting much, much closer. 

Dave Wattles, MassWildlife black bear and furbearer project leader, and members of his team visited the dens of 19 hibernating female bears during the months of February and March in central and western Massachusetts, discovering mother bears in good shape and high survival rates for their cubs and yearlings.

Now, the researchers are giving black bears another good bill of health at the close of their annual winter den checks.

“Survival is normally high, but there were only one or two cubs from last year that didn’t make it,” Wattles said. “I was almost anticipating a little more mortality.”

The bears are part of an ongoing research program that has been in operation for 39 years and that Wattles says has allowed MassWildlife to develop strong data on the survival and reproduction of black bears in the state.

How a den check is done

Using radio telemetry and GPS navigation, the research team tracks sows, or female bears, previously fitted with transmitter collars to their dens, which can be located in a variety of places, typically in brush piles, under fallen trees, in rock crevices and in tree hollows.

In more suburban areas, collared bears have been known to den in backyard woodpiles and under decks, as these spots are not frequently visited by people during the winter.

“We had one bear whose den was in an old historic cemetery, and you could see it right from the road in perfect view of the public,” Wattles said. “Another was a stone’s throw from (Route) 116 in Sunderland.”

But the bear dens are not often in plain view and can be difficult to reach. One bear with yearlings — which the team ultimately decided not to handle — had denned in the hollow of a tree 25 feet off the ground.

Bears that are not checked on in their winter dens will be tracked later in the spring to assess their status.

Once the den is located, biologists use a jab stick — a pole with a syringe on the end containing Telazol — to immobilize the sow in the den. It is the same drug used by veterinarians to anesthetize dogs and cats.

“This drug is well-known and has a very wide safety margin,” Wattles said. “If the first jab doesn’t work, and we need to do another, we can still give the full dose without any problems.”

After the bear is tranquilized, she is carefully removed from the den, and her vital signs are continuously checked and monitored.

As the bears are unable to blink when drugged, an ophthalmic ointment is placed in each eye, and a protective covering is placed on the head to keep dirt from getting into the eyes. The team then fully documents the condition of the bear.

“We will assess the body condition, get a weight and try to see what they have for muscle and fat reserves,” Wattles said.

Sows are weighed by being placed in a net attached to a spring weight scale and suspended from a horizontal pole supported by team members.

If cubs are present, they are carefully removed, counted, sexed, weighed, given a general health assessment and kept warm while other team members attend to the sow.

Yearlings that are present are also immobilized, and females are fit with expanding collars, to start their documentation in the study.

Life cycle

Black bears mate from mid-June to mid-July and give birth to tiny cubs in mid-to-late January during hibernation.

Bears have a unique survival strategy called delayed implantation. After mating, a group of cells or a blastocyst is formed but does not immediately get implanted in the uterus. Instead, it remains dormant until the female has gained enough weight to survive the winter and sustain her cubs. If this does not occur, the blastocycst will be absorbed and there will be no pregnancy.

Cubs will remain with their mothers for about 17 months, during which time the mothers teach them how to forage and escape from harm, among other important survival skills.

Black bears are able to reproduce at 3 years old but, many young inexperienced bears are unsuccessful at raising their first or second litters.

Young mother bears tend to have fewer, smaller and less robust cubs. They will often roam throughout their range with their cubs in tow, exposing them to various dangers along the way.

“Mature females will emerge from their dens and move right into wetland areas to find skunk cabbage, which is of huge importance to bears,” Wattles said. “They will park themselves in these areas for weeks at a time where they have water, food and protection.”

Wattles added that females get the hang of how to successfully raise cubs at around 5 or 6 years old.

“In her prime, at about 6 years old, a mother bear can produce two to four cubs. That number decreases into her late teens,” he said.

By studying black bears, biologists can track survival rates, the causes of mortality, reproduction trends, how bears are using and moving through their habitat, and how food availability affects their health and survival.

“We use the survival and reproduction studies of collared bears in 2011 to estimate a population of 4,500 bears,” Wattles said. “That estimate is now more likely around 5,000 to 5,500 bears.”

MassWildlife will be implementing a new study this spring using hair snares.

This involves stringing barbed wire in certain locations and baiting that area. When bears pass under the wire, their fur is caught on the barbs and then collected for DNA study. With the black bears’ thick layer of fur, the barbs don’t come close to their skin.

The new study will allow biologists to look at the genetics of the bear population, giving them yet another tool to better understand black bears in Massachusetts.




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