First one in the USA? Harwich Conservation Trust builds groundbreaking otter den

When otters were sighted at the Robert F. Smith Cold Brook Preserve after an ambitious eco-restoration project, Harwich Conservation Trust (HCT) Trustee Herb Raffaele put on his thinking cap.

Could HCT build an otter den that would provide a safe place for the playful mammals to raise their young? And could that human-made den be outfitted with an unobtrusive camera so otter fans around the world could tune into the action.

Raffaele swung into research mode, leveraging his considerable expertise as a noted ecologist, author of books on wildlife conservation and the birds of the Caribbean, and former chief of international conservation for the U.S. Fish and Wildlife Service. He was surprised by what he uncovered.

Den could be the first of its kind

“In Europe they have developed ways of building dens to make otters happy,” said Raffaele. “I’m not aware of anybody building a den in the U.S. This could well be the first in the country.”

After traipsing all over the Cold Brook Preserve, Raffaele found a promising site next to a pond and away from the trail. He reached out to folks in Europe who had successfully built otter dens, gathered design ideas and created a plan.

HCT Summer Intern Lucy Palmer worked on the camera angle, researching ways to install and power the device, and transmit the video.

This week, the plan became a reality. Braving sweltering conditions, HCT volunteers, HCT Director of Land Stewardship Connor O’Brien, Raffaele and Palmer built an otter den at the Cold Brook Preserve. The site looks extremely promising: otter scat was found nearby while the den was being built. “The otters have already been here,” said Raffaele.

During a break in construction, Raffaele explained the otter den design. “They need a chamber that is always above water level,” he said. “It has to be about 2 feet by 2 feet and at least 14 inches high.” For this component, HCT used cinder blocks with a metal roof, which has a trap door and a small opening that allows the camera to be installed inside the den.

Then, there’s the all-important tunnel connection to the den, created with 8-inch diameter tubing. “Otters need an entrance route into the water,” said Raffaele. “One tube is going to exit into the water. They can swim from the pond right into their den. They need an escape route, so we have a second tube that will go into the upland.”

Finding the right camera

The den and tubes were covered with earth. The only human-made object that will be visible in the area will be a solar panel to power the camera.

“The camera was tricky,” said Palmer, HCT’s Summer Intern. “It needed to be small, it needed to have cellular access, because we don’t have Wi-Fi on the property. and we didn’t want to have to retrieve an SD card from the camera, because it would disturb the animals.”

The camera also had to be weather-resistant and have infrared capabilities, because it will be located inside the dark den. 

Now, the otter waiting game begins. While the animals are present on the Cape year-round, spring is baby otter time, when the mustelids seek out dens to raise their young. That’s when Raffaele is hopeful that the groundbreaking HCT-made den becomes home to an otter family, and the camera provides must-see educational entertainment for wildlife watchers.

While a ton of work and research went into the project, one simple principle stood tall. “We had to think like an otter,” said Raffaele.

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