Black Bear Monitoring in New Hampshire

A radio-marked male black bear in Vermont investigates a potential mark tree at the onset of the breeding season. Bears are fitted with radio collars and GPS data loggers for various reasons in different states. This radio-marked bear in Vermont is part of an ongoing long-term study to measure the potential impacts of wind generation projects on black bear habitat use in that state. Courtesy of Vermont Fish and Wildlife.

As late spring transitions to summer, we typically think of our northern woodlands as bursting with abundant life. But for bears, June into early July is actually a very lean time of year. Early spring food diminishes in value as spring wanes: the emergent, succulent vegetation of spring and the buds and new leaf growth of aspen, ash, oak, and maple are becoming less palatable, and the leftover mast from the previous fall, such as beechnuts and acorns, are beginning to sprout. Soft mast – raspberries and blueberries, followed by blackberries – doesn’t become abundant until around mid-July to August.

“June is a challenging time for bears, from a food perspective,” said Andrew Timmins, black bear biologist for New Hampshire Fish and Game. “It’s also the month we begin to see an increasing trend in bear-human conflicts.”

Food abundance is a key driver of many population trends that Timmins monitors for the state. For example, beechnut production in the fall is closely correlated with reproductive success – the more abundant beech mast, the higher the number of cubs born the following spring (see chart). A bear’s home range and movement patterns may shift depending on food availability from year to year, and is influenced by multiple factors that include forest management practices, the diversity and quality of habitat, and weather.

In March, biologists visit bears in their dens to document the litter size and health of cubs. Cubs stay with their mothers for about 18 months, so den checks are conducted on the same animals a year later to determine the survival rate of the cubs. Here, NH Fish and Game biologist Andrew Timmins and Geographic Information Systems (GIS) specialist Katie Callahan interact with one of the new cubs born to a bear they monitored with a radio collar for 11 years. This particular mother bear was unusual in that she returned to the same den every other year four or five times to have her cubs; typically females do not use the same den. Courtesy of New Hampshire Fish and Game.

Biologists use radio collars to monitor bear survival, home range size, habitat use, reproductive success, litter size, and the survival of cubs over time. Data collected from these collars are used to develop some of the metrics used in population modeling. These models show trends over time and help wildlife managers determine whether or not the state is meeting its management objectives.

“Female bears are most valuable for tracking bear population dynamics because their survival and productivity drives growth or decline,” said Timmins. “The more dominant males breed multiple females, so younger males don’t play as much of a role in population rate of change.”

In the New Hampshire bear monitoring program, GPS data loggers on collars are used to record multiple locations per day that provide insight on daily and seasonal locations and movement, different types of habitat used throughout the year, and home range size (see map showing the movement of one tracked bear over the course of one month).

If a collar fails to record any new GPS points over the course of 12 hours, this signals something has gone wrong, either mortality for the bear or a dropped collar (collar drops and malfunctions are generally infrequent).

The green line shows beech mast abundance subjectively ranked on a scale of 1–10 (poor to excellent). The brown line shows the percentage of females in a sample population that birthed cubs. High mast production leads to a greater percentage of breeding-age females producing cubs the subsequent January. Biologists can measure age and reproductive success through the analysis of bear teeth – similar to aging a tree. In each year of a bear’s life, a layer of cementum (calcified tissue layer) is laid down on the tooth. For each year that a sow has cubs, the space between layers is notably narrower, as much of her resources go into the cubs’ growth. A cross-section of the premolar allows biologists to identify years when cubs were produced and nursed.

When bear-human conflicts occur, they typically originate from human behavior. If people have food attractants near their house (or campsite in parks or recreation areas – a common issue mid-summer into fall), they are drawing bears into the potential for conflict, which can lead to a bear being shot by a disgruntled homeowner, lethal removal by the management agency (due to habituated behavior caused by routine access to human-related food attractants), or increased fatalities by vehicles.

“Bears are just trying to do what they do best, and that’s find high-quality food,” said Timmins. “It’s up to us as a society to be proactive, to not attract them.”

In 2020, the New Hampshire bear population experienced a high harvest, partly because of lack of food resources – bears travel farther to find food during lean times – thereby becoming more vulnerable to hunters, and partly due to increased hunting pressure.

Monitoring provides information on the amount of ground bears can cover and where they exploit natural food resources. They have good memories and will revisit areas where they have successfully found food in the past. This particular map shows the activity patterns of a radioed rehabilitated bear (labeled R132 for research purposes) after release. The cluster of purple dots shows where the bear spent a lot of time in early successional forest habitat, likely filling up on raspberries that regenerated following a timber harvest. If it’s a bad mast year within their home range, bears will travel well out of that range to take advantage of concentrated mast crops in other areas. Courtesy of New Hampshire Fish and Game.

Years of collecting data on radio-collared bears show the New Hampshire bear population is likely more robust than historically thought; biologists are documenting larger litter sizes and bears breeding at a younger age. They’ve also found that if a sow loses cubs during spring or early summer (born in January, the cubs typically stay with the mother bear for 18 months), she may breed that same summer and have cubs the following January. This represents a significant reproductive contribution. The resilience of the population depends on good-quality habitat, corresponding natural food abundance, and the ability of bears to exploit landscapes and food availability.

Timmins attributes the success of New Hampshire’s bear population to proper management of diverse habitats; perhaps one year a particular area may not have a good fall nut crop, but that same area may have good soft mast crops. Current trends to manage for young forests by large and small landowners can benefit bears by providing earlier successional foods, as berry-producing species invade disturbed areas. However, this needs to be balanced with the proper management for mature forests for production of fall mast that is high in fat and protein – both habitat types are important to bears at different times of the year.

Additional Resources

In 2021, 40 orphaned black bear cubs were released back to their natural habitat in New Hampshire and Vermont from the Kilham Bear Center in Lyme, New Hampshire. Read more about their work here.

New Hampshire Wildlife Journal (December 2019) featured an article by Ben Kilham on bear behavior, why cubs are orphaned, and ways to avoid conflict.

Something’s Bruin in New Hampshire offers myriad tips on living with bears and avoiding conflicts.