In the latest reflection of the state’s exploding bear population, wildlife officials discovered a den in Central Massachusetts inhabited by three bears, and they attached ear tags and radio collars to the mother and three cubs.

The operation last week was part of a long-term study by the state’s Division of Fisheries and Wildlife to monitor and track the movements of the bear population. An estimated 4,500 black bears now live in the Commonwealth, the highest since pre-Colonial times, according to state officials.

“We want to see how [the bears] are doing,’’ said Dave Wattles, a biologist for the division. “So we go weigh them, check their condition, and determine the sex of the cubs.’’

The state does not disclose the location of the dens to protect the bears.

By using ear tags and radio collars, officials can keep track of how the animals do over the year, Wattles said.

“We check in when they hibernate, see how the mother is doing, and which cubs survived that might add to the population,’’ he said.

The number of black bears reached as low as 100 individuals in the early 1970s, but has been rising steadily amid greater reforestation efforts.

“Black bears’ natural habitat is the forest. So when colonists turned the forest into farms, their habitat and the population retreated to the western parts of the state,’’ Wattles said.

“As reforestation efforts have gone into effect though, we’ve seen a huge resurgence west of the Connecticut River.’’

The Connecticut River has long served as an artificial boundary to bear territory, but rising populations have caused bears to move eastward in the last 15 years, he said.

“For them, it’s an issue of space. A female west of the Connecticut can control between 8 and 12 square miles. In the east, it can be 77 [square miles],’’ he said.

Wattles reminded the public that as the number of bears grows, encounters with humans could become more common.

“The best thing you can do to keep your property safe is to secure your trash or anything a bear might see as a source of food,’’ he said. “It’s when bears start to associate people with food that conflict arises.

“If you see a bear, speak to it in a calm voice, back away, and enjoy the sighting,’’ he added.

Andrew Grant can be reached at andrew.grant@globe.com.