Beavers help shape New Paltz’s Mill Brook Preserve

This dam, constructed by beavers, stretches the length of a large pond within the Millbrook Preserve in New Paltz. (Photos by Lauren Thomas)

Beavers serve as nature’s hydroengineers, creating ponds and lakes, diverting streams, slowing stormwater runoff and designing landscapes that welcome a myriad of waterfowl and fauna. Not the least of these is the great blue heron, which can often be seen perched in or around the beaver lodge at the Mill Brook Preserve in New Paltz.

Walking or running around this preserve – an oasis in the middle of New Paltz, sandwiched between a continuing-care center for the elderly and an elementary school, along the Mill Brook stream (Tributary 13) – provides its daily dose of beaverdom. There are new trees felled, others being stripped, dams being packed with mud, and lodges being abandoned or built. There is also a network of canals that the beaver have dug hundreds of yards into the woods, where they can drag and then float the branches and tree limbs that they’ve sawn off with their toothy grins to whatever aquarian project they are working on. There are freshly scraped and girdled tree trunks with piles of wood shavings spread about, often in a circle or semicircle, as though the creatures were attending nightly carpentry classes and donning hardhats with headlamps while the rest of the world sleeps.


Each day is like a beaver Advent calendar, with excitement building toward a full completed dam or the discovery of a felled tree or the rare-but-spectacular sighting of one of these creatures slinking about the pond – or, even more fantastic, slapping their paddle-shaped tails (up to nine inches long and six inches wide) against the water to let you know that they mean business.

Since beavers do most of their work at night, catching them in the industrious act of woodworking or lodge-making is no easy task. It can make one beaver-crazed, hiding out at twilight to catch a glimpse of these 25-to-65-pound mammals working their magic.

What to do? Ask the New York State Department of Environmental Conservation (DEC) about these curiously round, mightily busy and buck-toothed beavers. Here’s what the DEC specialists had to say.

There is lot of evidence in Mill Brook Preserve of trees taken down by the beaver population.

An amazing creature

Biologist Ken Frazier noted that beavers have special incisor teeth “that never stop growing to compensate for being worn down.” These large teeth, which can grow up to four inches long with only a half-inch above the gumline, combined with an “extra-heavy skull and strong muscles, can chisel through the hardest wood.”

Their teeth are orange, which doesn’t mean that beavers have bad hygiene. It just means that they have more iron in their chompers to fortify their gnawing ability. According to Frazier, the orange front side of the beaver teeth are harder than the back side, so that the back side wears faster than the front. “This allows for the tooth to maintain a chisel shape for cutting through wood.” They also have lips that close behind the incisors to allow the beaver to munch underwater.

These aquatic animals have webbed hind feet, which, along with their rudderlike tails, add to their supreme swimming ability. According to the DEC, beavers’ flat tails, besides aiding their ability to navigate the water, are also highly vascularized, helping to minimize heat loss and keep their bodies warm while also working to store fat for the lean months.

As for their dam engineering, the DEC points out that beavers build dams because the more water they are surrounded by, the safer they are from predators. “Water is their preferred habitat,” said Frazier. “Water equals safety for the beaver. The less time they spend on land, the longer they live.” 

That is why they are found inhabiting wooded streams, along the margins of lakes (like Lake Awosting and Tillson Lake in the Minnewaska State Park or along Tributary 13 near the Wallkill Valley rail-trail off Huguenot Street) ponds, reservoirs, swamps and marshes.

Construction engineers at work

In fact, beavers prefer swimming up to a tree to cut it down over getting up on the bank, where they might be exposed to and vulnerable to predators such as coyote, bobcats, fishers, dogs and humans. Beavers at one time were trapped and killed almost to extinction because of their fur and oils. To this day, human impact – including trapping, development and vehicular traffic – is the number-one threat to nature’s wetland engineers.

They create dams by interlocking branches they they’ve chewed off with other debris, and then packing the fascia with leaves and mud. Dams can include branches, cornstalks, rocks, leaves, and sometimes might incorporate a repurposed feature like car axles and glass bottles that littered the forest floor and banks of the pond.

Although they’re not particular about species of trees for dam-building, beavers prefer to eat the leaves, barks and twigs of “soft” hardwoods such as aspen, willow and cottonwood and a variety of herbaceous plants. As winter approaches, they will often collect and store cache food items (referred to as a “raft” or “feedpile”) underwater near the entrance to their lodge, so that they don’t run out of food if the ice freezes over and keeps them submerged in their winter cabins.

These elaborate lodges have multiple entrances. Depending on the type of habitat they reside in, the critters can create a home streamside, lakeside or out in the open water. Their living quarters are above the level of the surrounding water. Because of their unique ability to fell trees, beavers can make these lodges warm and airtight through careful lacing of logs, sticks and twigs, along with their mud-and-leaves mortar. These are end-of-day bunkers, with their inhabitants locked and loaded to begin construction or repairs at the sound or motion of running water.

Inside beaver lodges are typically the parents, who mate for life, their present year’s offspring, possibly a few teen beavers from the previous year’s litter, and the occasional aunt or uncle or nomadic adult that they’ve taken in. The average number per lodge is between four and eight individuals, but can amass up to a dozen. Litter size ranges from two to seven kits, who are born fully furred with eyes wide open and can enter the water a few hours after leaving their mother’s womb.

There are two lodges located fairly close to each other on a pond in the Mill Brook Preserve. Those in the know say that it is likely only one is active at present.

A keystone species

Beavers are certainly waste-not/want-not creatures who will often utilize the remains of an old lodge or abandoned lodge for a new home. According to Frazier, how long they occupy a den can vary depending on how rich their surrounding habitat is. “It’s extremely variable, but on average about five years,” he said. “In a quality habitat, sites can be occupied 30 to 35 years out of a hundred.” Mostly, beavers abandon sites when food availability becomes too low or the lodge begins to rot over time.

The habitats that beavers create with their dams produce rich and viable ecosystems for muskrats, minks, otters, raccoons, wood ducks, mallards, black ducks, teals, kingfishers, great blue herons, green herons, brook trout and various frog and salamander species. They also invite a variety of flora and fauna, including cattails and water lilies.


Though these magnificent animals were once considered valuable solely for their pelts and oils, or as “pests” for flooding roadways, beavers are now being deemed “a keystone species” by scientists. Besides providing critical wetland habitat, beavers dams slow the flow of water, which reduces erosion and actually decreases flood damage downstream. Their impoundments also allow water to sink into the ground and replenish the water table, while also filtering out silt and pollutants that biodegrade behind the dam.

Watching their work, day in and day out, is mesmerizing and somewhat mystifying. They do almost all of their felling and building at night. But in the mornings things have shifted, and the mosaic they helped to paint and the frame they’ve built around it is slightly altered. The only clue could be a dam elongated, a slow leak, a fresh cut, wood shavings underfoot, or that flash of a paddle tail or those brown eyes darting just above the water and then submerging again.

There is one comment

  1. Rich

    Thanks for a great article, Erin. I send a lot of time in the preserve and now I have even more information and perspective on these amazing animals and the role they play. You actually answered many of my long standing questions. Thanks again!

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