Overview:
The Massachusetts Department of Conservation and Recreation (DCR) used infrared-equipped drones to count deer in Quabbin Park, confirming that deer numbers were high enough to threaten forest health and justify a managed hunt. The two-day controlled deer hunt in December resulted in the harvest of 24 deer, reducing the density from 24 to 32 deer per square mile to 16 deer per square mile. DCR aims for a deer density of 20 deer per square mile to protect forest regeneration. The experiment may help DCR refine deer management across the watershed.
After questions from residents last summer about whether a deer hunt at Quabbin Park was necessary — and whether the state’s methods for counting deer were reliable — the Department of Conservation and Recreation turned to a new tool: infrared-equipped drones.
The result, DCR officials told members of the Water Supply Protection Trust on Thursday, was a more precise snapshot of the deer population that ultimately reinforced what earlier surveys had already suggested — that deer numbers in Quabbin Park were high enough to threaten forest health and justify a managed hunt.
Quabbin Park is part of the larger Quabbin Reservation, a vast protected landscape in central-western Massachusetts that surrounds the Quabbin Reservoir, the primary water supply for greater Boston. Created in the 1930s, the reservation was largely closed to hunting for decades, a policy that allowed white-tailed deer populations to grow well beyond sustainable levels, according to DCR.
To protect forest regeneration and water quality, the state began two-day controlled deer hunts in parts of the reservation in the early 1990s, gradually scaling back hunting as populations declined. Quabbin Park was added as a controlled hunt zone in 2024, with hunters selected through a lottery and the park closed to the public during the hunts.
Ken MacKenzie, director of natural resources for DCR’s Division of Water Supply Protection, said deer density estimation — the core question behind whether hunts are warranted — is “one of the most fundamental tools in wildlife management,” but also one of the most debated.
“It’s long debated, and it is a hot topic in wildlife management,” he said, noting that biologists across the country rely on a mix of methods, from helicopter surveys and trail cameras to harvest data and counts of deer droppings, known as pellet group surveys.
Since 2015, DCR has used pellet counts at Quabbin Park, conducted after the leaves fall, to track population trends. Those surveys averaged about 56 deer per square mile over several years and produced a 2025 estimate of 26.8 deer per square mile, with a wide range.
“I’ll tell you or remind you,” MacKenzie said, “any deer density greater than 20 deer per square mile has an impact on forest health and regeneration, and is usually a good indicator that deer management is necessary.”
Still, that method came under scrutiny. At an August 2024 stakeholder meeting hosted by former DCR Commissioner Brian Arrigo and Rep. Todd Smola in Ware, attended by several hundred people, residents questioned whether pellet counts reflected what they personally observed in the park.
“As a result, we agreed to study, to undertake another independent study, to try to get a better deer density estimate,” MacKenzie said.
DCR partnered with the Massachusetts Department of Transportation’s Aeronautics Division to fly drones equipped with thermal infrared cameras over Quabbin Park. The technology, MacKenzie explained, allows autonomous flights over large forested areas and makes warm-bodied animals stand out clearly against cooler backgrounds, especially in winter conditions.
The roughly 2,600-acre park was divided into 22 flight transects, launched from Quabbin Tower to maintain visual contact and comply with federal aviation rules. Two pre-hunt flights, conducted Nov. 24 and Dec. 1, estimated deer density at between 24.4 and 32.7 deer per square mile — closely aligning with the pellet survey results.
The two-day controlled hunt at Quabbin Park took place Dec. 8 and 9, resulting in the harvest of 24 deer — about a six-deer-per-square-mile reduction. A post-hunt drone survey conducted Dec. 17 estimated the remaining density at 16 deer per square mile.
“So after the hunt, we went from about 24 to 32 deer per square mile to 16 deer per square mile,” MacKenzie said, adding that another round of flights is planned in January to further refine the estimate.
Water Supply Protection Trust members reacted enthusiastically to the presentation. Vandana Rao, director of water policy at the Executive Office of Energy and Environmental Affairs, called the technology “so cool” and asked what density DCR considers acceptable.
“Twenty deer per square mile is what we’re shooting for,” MacKenzie replied. “Anything higher than that is when we start to see impacts on forestry regeneration.”
Beyond the Quabbin Park debate, MacKenzie said the experiment could help DCR refine deer management across the watershed.
“We’re hoping we can use this technique in other parts of the reservoir,” he said, calling the effort a way to better understand both the park and “the critters that are running around in there.”