North American River Otter
The North American river otter (Lontra canadensis) is one of 13 species of otter worldwide. Otters are in the mustelid, or weasel family. They inhabit every continent in the world except Antarctica and Australia. All otters are semi-aquatic, living in or around ponds, lakes, river, or the ocean.
The North American river otter is the only species of otter that lives in New York State. Its range includes Canada and many parts of the United States. This otter is generally between 3 and 4 feet long, including the tail, and weighs 10-30 pounds. The otter spends most of its time in or near water. It is well adapted for swimming with a broad, flattened head and a long, slender body. The otter's tail, which is about 1/3 of the overall length, is extremely muscular and is used for swimming and for balance.
Pelt and Fur
The otter's dark brown fur keeps the otter warm and dry even in chilly winter waters. Hollow, oily guard hairs help with streamlining and waterproofing. Underneath is a layer of downy fur that holds warm air bubbles against the skin when the otter goes underwater. In order to maintain this fur, the otter must spend time caring for its coat and will make a roll out of moss or grass that it uses like a towel. The dense, shiny fur of the otter makes it highly prized in the fur market. The otter pelt is used as the standard by which all other pelts are judged in the garment industry. Trapping has had important impacts on the New York otter population in the past.
Swimming
Although otters are swift runners, they are most agile in the water. Their sleek bodies, short powerful legs, and webbed feet make otters very acrobatic swimmers. When the otter is swimming on the top of the water, it is using its webbed feet in a dog-paddle fashion to move around. While underwater, the hindquarters will undulate much like a swimming dolphin. The otter will also use its thick, muscular tail to make sharp turns, but its feet and neck do most of the steering.
Otters primarily use eyesight when chasing prey underwater. An otter's eye has a lens that is specially shaped for underwater vision. In murky water, when they cannot see well, otters can still hunt effectively because they have highly developed whiskers that can sense vibration. Otters are also adapted to underwater swimming with the ability to close their ears and nostrils.
Diet
Otters are very efficient predators, feeding on just about anything they can get their paws on. Their speed and agility in the water allows them to quickly fill their bellies and spend the rest of their time playing. About 80% of the river otter's diet is made up of aquatic organisms like fish, crayfish and aquatic insects. Otter will also prey on frogs and semi-aquatic animals like young birds, turtles and occasionally, small beaver. While the otter is most adept at catching aquatic animals, it will sometimes prey on land mammals and birds. Otters have even been known to eat berries and fruit if fishing is poor.
Some fishermen dislike otters because they eat trout and other game fish. Otters, however, tend to go after slower species of fish such as sunfish more often than the faster trout. The only time otter have been reported to do damage to a fishery is in a confined area like a small pond or a hatchery. An otter who finds such an abundance of food in a small area may go on a killing spree and kill more fish than it can eat.
Home Range
Otters usually live alone in territories that are about one square mile. Although otters are territorial, they have never been reported to be unfriendly toward each other. They simply tend to avoid each other through scent marking. Scat and scent marking is a way of communicating between otters as to the location of territories.
Sometimes otters live in groups. A mother otter and her kits live together in a family group for about one year, and rarely males will form clans that hunt together.
An otter may cover a home range of 10 square miles or up to 30 miles of shoreline in one year. When traveling from one pond to another, otters will usually move along rivers or streams instead of going over land. In the spring, however, as young otters venture out to find their own territory, they have been known to travel long distances over land.
Reproduction
Otters mate in March or April and kits are born about one year later. This is because otter eggs have delayed implantation. The eggs are fertilized in the spring but do not attach to the uterine wall until two months before kits are born.
The female otter gives birth in March or April to a litter of two to four young. The kits are born blind but fully furred. After three weeks, the kits' eyes open, but they continue to nurse until they are about seven weeks old. After two months of living in the den, the kits venture out to explore the water. The kits must be taught to swim and are reported to bob like corks in the water, as their fluffy fur holds air bubbles, keeping them afloat.
Young otters and the mother form a family group in which the young learn how to swim and hunt. In rare cases the male parent will help raise the young. The family group remains together for about 13 months, or until the kits can fend for themselves. At this point, the young otters will disperse to find a home range of their own.
Only about half of the litter will make it to adulthood at two to three years old. Those that survive can live up to twelve to fifteen years. Studies have shown, however, that otters are not tolerant of polluted ecosystems. Biologists are concerned about some contaminants in aquatic systems that may harm otter populations.
Tracks and Sign
Otter tracks and sign are very easy to identify once you know what to look for. An adult otter will leave tracks that are about 3 inches wide and round in shape. Otters have claws and webbed feet with five toes on each foot.
In addition to looking closely at individual tracks, it is important to look at the overall picture, or the pattern of tracks. Otters, like all of the weasel family, are bounders. This means that when they run, their hind feet come up to meet their front feet. This leaves a unique pattern of tracks. Otters also slide on snow, ice, or mud banks, leaving a trough about 6 inches wide.
As well as tracks, scat (feces) is another sign to look for. Otters will use a prominent location like a rock or a peninsula of land as a latrine or toilet site. One or more otters will return to the same site many times, leaving an area with a large amount of scat. Fresh otter scat is dark and wet and often contains fish scales and small bones.
