Catching Up With the Beavers

As Loggers, Swimmers and Homemakers, These Animals Are Unmatched

  • A beaver eating leaves. Mary Holland photograph

    A beaver eating leaves. Mary Holland photograph

  • A beaver eating leaves. Mary Holland photograph

My fascination with beavers began many years ago at Quabbin Reservoir, a 39-square-mile body of water in central Massachusetts that was created, in part, as a water supply for Boston.

The residents of the four towns that were flooded to make this reservoir were forced to leave the area, but other creatures quickly took advantage of the newly-made lake and surrounding wilderness. In the past 75 years Quabbin has provided habitat for nesting common loons, at least one mountain lion and countless other more common animals — including beavers.

I was fortunate to grow up on a road that dead-ended right at the reservoir, and I spent a lot of time exploring this area. One early spring day soon after ice-out I located an active beaver lodge on the bank of a small cove. Accompanied by my chocolate lab Thornton, I climbed up on top of the lodge and put my ear to the vent, which serves as a conduit for fresh air. To my delight, I heard the squeals of very young beavers coming from within the lodge.

At that moment a beaver surfaced a few feet away from us. It made eye contact with both me and my dog and then turned and swam away from shore toward the middle of the reservoir. My water-loving dog quickly realized that this was an invitation he couldn’t resist, and into the icy water he plunged.

The beaver then applied more steam. These animals can swim up to five miles per hour. Thornton was intent and seemed to be gaining fast. But then the beaver disappeared, and almost simultaneously another beaver appeared much farther out. Clearly one beaver was being spelled by another.

Unfazed, Thornton surged ahead. Again, when he got close to the beaver, it dove, and a different beaver popped up even farther out.

All this time I was calling Thornton at the top of my lungs, but he was so intent on reaching the beavers that I doubt he even heard me. I realized there was no way I could convince my dog to turn around, and I feared that the beavers were never going to stop this game of tag.

Eventually I ended up diving into the exceptionally cold water to retrieve Thornton and pull him back to land.

After getting home I did some reading and learned that I had just witnessed a classic defense behavior that beavers display when they have young and feel threatened. Alternating with each other in the water, two parent beavers entice a predator to follow them. They swim out as far as necessary to exhaust and eventually drown their pursuer.

Needless to say, my interest in beavers was piqued by this experience.

Beavers have a dubious reputation. Yes, they are rodents and therefore related to rats. They can be destructive. And it is possible to contract beaver fever — Giardia parasites — by drinking contaminated water from a beaver pond. I know this from personal experience.

But the many adaptations and habitat-creating abilities of this semiaquatic mammal, in my opinion, far outweigh their more negative characteristics.

Valves in the ears and nose close automatically when a beaver submerges. A third, transparent eyelid, or nictitating membrane, extends across each eye to protect it from debris and enhance underwater vision. Nostrils, eyes and ears are aligned such that most of the beaver’s body can remain submerged and hidden while it swims. A beaver’s lungs can exchange 75 percent of the air they inhale, compared to the 15 percent humans are capable of — which means that beavers can stay submerged for up to 15 minutes.

Equipped with four large, continuously-growing incisors, a beaver can fell trees six inches in diameter in less than 50 minutes. Fur-lined lips that close behind the four front incisors allow a beaver to gnaw under water. Castor glands secrete a scented substance known as castoreum, which beavers smear on mounds of leaves and mud they build to communicate with each other. Anal glands produce oil that beavers use to waterproof their fur.

Their large, webbed feet are designed for paddling. A split nail on each hind foot doubles as a comb for beavers to groom themselves with and as tweezers to remove splinters from their teeth.

The beaver’s flattened tail is an impressive device. It stores fat for winter sustenance and in the summer serves as a pretty efficient heat exchanger that releases 25 percent of a beaver’s body heat. It also acts as prop, or third leg, when the beaver stands on its hind legs to cut down a tree, and signals alarm to other beavers when slapped against the water. When a beaver is floating on top of the water, its tail is a handy rudder and balancing aid.

These adaptations explain why beavers have made such a comeback after being trapped almost to extinction in North America.

Moreover, the architectural and building skills of beavers are surpassed only by those of humans. Their dexterity and ability to construct dams, lodges and canals are mind-boggling. The beaver’s lodge is a relatively secure home, approachable most of the year only by animals that can swim and impossible to break into during winter. Beavers also create habitat for innumerable other creatures. For the 10 to 25 years that a beaver pond is usually active, it serves as habitat for birds (especially cavity-nesting), fish, turtles, snakes, salamanders, frogs, crayfish, insects, otters, mink, raccoons, white-tailed deer, black bears and muskrats — to name a few. Aquatic and wetland plants thrive as well.

Is it any wonder that I seized the opportunity to instill a love of beavers in young children by writing The Beavers’ Busy Year? Every aspect of a beaver’s life offers a fascinating glimpse at the miracles achieved through evolution. Despite nearly freezing to death during my early-May swim with beavers, I am grateful that my adventure inspired a lifelong interest in this remarkable rodent.

A New Book

My newly-published, book The Beaver’s Busy Year, by Mary Holland, describes the seasonal life of beavers for young children. It includes dam and lodge-building, diet, preparation for winter, grooming, spring emergence from the lodge and birthing. Also covered are the adaptations of various body parts such as teeth, tails, eyes, noses and fur and how they equip beavers for their semi-aquatic life. A special section presents various beaver signs where the reader can match photographs with written descriptions of tracks, winter food supply pile, scent mound, canals, incisor marks, lodge, scat and beaver-cut trees. Additional sections discuss beavers as habitat engineers, dam builders and keystone animals. The publisher, Arbordale, has posted beaver-related cross-curricular teaching activities and more on its website:

Mary Holland is the author of “Naturally Curious: A Photographic Field Guide and Month-by-Month Journey Through the Fields, Woods, and Marshes of New England,” “Milkweed Visitors,” “Ferdinand Fox’s First Summer” and “The Beavers’ Busy Year.” She has a natural history blog which can be found at .