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River Otters in Cambridge
DRAFT: by Michael Arnott
Appalachian Mountain Club, volunteer naturalist
Friends of Alewife Reservation, steering committee member
(added to website April 11, 2004)
I like to go looking for signs of wildlife a day or two after it has snowed. The last snow of the 2003-04 winter season provided a good opportunity. My favorite local "wildland" is the Alewife Reservation, just behind the Alewife MBTA Station in North Cambridge. The Reservation is home to a surprisingly diverse wildlife community. The mammals alone including mink, long-tailed weasel, eastern coyote, gray fox, red fox, and sometimes beaver and white-tail deer, as well as the usual smaller mammals such as rabbit, woodchuck, muskrat, raccoon, striped skunk, gray squirrel, white-footed mouse, short-tailed shrew, and meadow vole.
As I walked the path along the north side of the Little River I discovered tracks and slide paths coming and going from the river. The tracks and slide paths were bigger than mink or long-tailed weasel could make and had the distinctive tail drag marks of a river otter. Out came my camera. A couple of days later I showed my photographs to David Brown, the naturalist and environmental educator who had inventoried the Alewife Reservation's wildlife for the Biodiversity Study of Alewife Reservation Area: Species, Habitat, and Ecosystem, a Friends of Alewife Reservation (FAR) guidebook funded in 2002 by a Massachusetts Riverways Program grant. He confirmed that what I had found were the tracks and slide paths of river otters. He had suspected river otter were in the Reservation when he did the survey, but had not found clear evidence of their presence at that time.
North American river otters (lontra canadensis), one of the larger members of the weasel family, were once common in North America until habitat destruction and hunting for their fur almost drove them to extinction. They are making a slow come back. Zoo New England's Stone Zoo in Stoneham has a pair of river otters as part of its participation in the Species Survival Plans (SSP) program. SSPs are cooperative population management and conservation programs for selected species at North American zoos and aquariums. Each SSP carefully manages the breeding of a species in order to maintain a healthy and self-sustaining captive population. Institutions participating in an SSP also work together in research, public education, reintroduction of endangered species to native habitats, and field projects.
I was amazed to find these unique, semi-aquatic mammals living wild in the City of Cambridge. River otters can weigh up to 30 pounds and from nose to tip of the tail can be three and a half to four feet long. They have dense brown fur that keeps them warm, streamlined bodies, thick tapered tails that can be almost half their total length, and short legs. River otter's have small ears, and nostrils that can close underwater. In the wild, river otters have a life expectancy of 10 to 15 years. How they got to the Alewife Reservation is a mystery, but they can travel long distances overland if they do not get hit by cars or caught by coyotes.
Like other aquatic mammals such as beavers, river otters are great swimmers and can stay underwater for up to eight minutes. They can also run fast on land, something a waddling beaver would be hard pressed to do. Known for their playful nature river otters enjoy water games, mud and snow sliding, and tossing pebbles around. If one hopes to see them at play, the best time, as it is for many animals is at dawn and dusk. River otter's seemingly boundless energy means they have to eat a lot of fish. Fortunately the Reservation's Little River and many ponds have an abundant supply of common carp. Carp are an introduced, non-native species. They are bottom-feeders, destroying aquatic plants and increasing suspended sediments as they feed. Carp damage fresh water habitat for a variety of native species such as the Alewife herring that try to return every year from the ocean to spawn in fresh water habitats like the Alewife Reservation.
The Alewife Reservation's river otters probably have a bank burrow with an underwater entrance that leads to an above water line den. In the spring, river otter pups are born, usually two or three in a nest of dry vegetation within the den. River otters are born with a full coat of fur but blind and toothless but are ready to leave their parents after about eight to twelve months.
The size of a river otter home range depends on how much food is available. In addition to fish, their favorite food, river otters will eat an occasional frog, crayfish, turtle, and aquatic plant. The Alewife Reservation may only big enough to support one river otter family. While they may have only one den the river otters are themselves constantly on the move. One day they could be in Little Pond and the next day in Blair Pond, if the water level is not too low.
River otters are loners, unless it is a father and mother with young. March and April are the months river otter pups are usually born. Usually two or three young are born in a nest of dry vegetation within the den. River otters are born with a full coat of fur but blind and toothless. The pups are cared for by their mother and are weaned at about three months of age, after which both parents assist in their care, protection, and teaching them to swim. The pups leave their parents after about eight to twelve months.
I hope the river otters will survive and contribute to the Alewife Reservation's wildlife diversity. I believe the state's Department of Conservation and Recreation master plan for the Reservation, which include a storm water separation basin, will not harm the river otters. It should even improve their habitat's water quality. But I am afraid the plans for commercial or residential development of the adjacent Belmont Uplands Silver Maple Forest will endanger the river otter. While the Belmont Uplands is private property, it is also an inseparable part of the Alewife Reservation's ecosystem. I hope a property swap arrangement can be worked out with the developer that owns the Uplands so that the over 90 bird species including red-tailed hawk, woodcock, and great horned owl, at least 17 mammal species, and the alewife herring after which the Reservation is named.
May the towns of Belmont and Arlington, and the City of Cambridge that border the Alewife wetlands and woodlands continue to enjoy and benefit from this incredibly accessible environmental education resource. As evolutionary biologist Stephen J. Gould said, "We cannot win this battle to save species and environments without forging an emotional bond between ourselves and nature - for we will not fight to save what we do not love."
For information about the Alewife Reservation, the Biodiversity Study of Alewife Reservation Area guidebook and upcoming FAR events and walks including a May 1, 2004 Alewife Reservation Clean-up and a May 26, 2004 Edible Wild Plants Walk with Russ Cohen, go to www.friendsofalewifereservation.org or call FAR at (617)547-1944