There may be a beaver or two in residence in the Alewife Reservation in North Cambridge.

A beaver bank lodge and beaver-cut saplings were seen on a nature walk sponsored by The Friends of Alewife on Dec. 29 on the south bank of the Little River. About 20 children,siblings and parents observed and listened to some of the history and habits of these creatures during the holiday family walk.

 The beavers, if they are still there, don’t seem to be making an effort to construct a dam on the Little River, but the sapling area looks like a miniature clear-cut. More than a dozen small trees have been recently cut down in classic beaver style, and fresh mud insulation has been added to an old beaver bank lodge. Before Europeans came to North America, it is estimated that there where at least 60 million and some estimate 200 million beavers in what is now the continental United States. Only Florida’s alligator country did not have a beaver population. There must have been thousands of beavers in the greater Boston area. The demand for beaver fur to make hats and coats almost drove the beaver to extinction. I would be surprised if there are now more than one or two dozen beavers in the Greater Boston area. The beaver is North America’s largest rodent. Completely vegetarian, the beaver eats leaves, roots of water plants and the inner bark of various trees. The beaver is also quite the family animal, they mate for life and — while young beavers will usually leave the family lodge by the age of 3 — they are often welcomed back if they can’t make a go of it on their own.

But everyone is expected to help out keeping lodge and dam in good repair and raising the new kits that are born in the spring. The Cambridge Public Library has several good books and videos on beavers in its collection or that they can get through the Minuteman Library Network. My favorite is " LilyPond: Four Years with a Family of Beavers " by Hope Ryden. It reads like a mystery novel. It’s chock full of facts but almost impossible to put down. There are two good children’s books on beavers. My 7-year-old daughter preferred " Beaver " by Glen Rounds, most of which she could read herself. She also liked " The Beaver " by Sabrina Crewe which is more of a grade-school science book with photographs. The two videos I found are "Beavers: The Biggest Dam Movie You Ever Saw! " and " The Business of Beavers. "

 A second phase of the walk was conducted with Peter Alden and Karsten Hartel, two of the region’s most noted naturalists. Alden is with National Audubon, and Karsten is with Harvard’s Natural History Museum and author of an atlas on northeastern fish.

FAR will be conducting more walks in the Alewife Reservation in March and April, and on Biodiversity Days in June. For more information, contact Ellen Mass, FAR President, at 617-547-1944.