North American River Otter

Lontra canadensis
American River Otters Picnic Springs

The river otter belongs to the weasel family, and is equally versatile in the water as on land. It can be seen on the refuge in many of the ponds, streams and lakes. It establishes a burrow close to the water's edge in river, stream or lake. At the refuge, it has been seen living beneath a dam (a muskrat's den) and between rocks next to a spring. The den typically has many tunnel openings, one of which generally allows the otter to enter and exit the body of water. Female otters give birth in these underground burrows, producing litters of one to six young.

The North American river otter is a predator. Fish is a favored food among the otters at the refuge due to its availability. An adult otter can eat up to 2 to 3 lbs of fish per day. Insects and small amphibians (like frogs) are also consumed. The otters usually like the small and more abundant fish rather than the larger trout. Instances of river otters eating small mammals and occasionally birds or ducks have been reported as well.

River otters are well designed for life in the water. They are streamlined with small heads and a neck the same width as the head. The ears are round and small and don't protrude so they reduce drag while swimming. Their legs are short and strong and their toes are webbed. They have thick fur (375,000 hairs per square inch) that serves them well in cold temperatures. They have long guard hairs that remain pliable in very cold weather, and the dense underfur traps air to insulate it in water. The Northern River Otter can dive to 45 feet and stay underwater for minutes.

Otters have specialized teeth, including sharp canines and carnassials (modified fourth upper premolar and the first lower molar) that inflict lethal bites to prey. Also, river otters have large molars used for crushing hard objects, such as the shells of mollusks. An adult river otter has a total of 36 teeth.

River otters are active all year and prefer to be active during the dusk, night and dawn hours. They are quite active as they move through the water in search of food and climb onto land to dry, eat, do bathroom duties and to rest. They get by on land very well by walking, running, bounding, or sliding. They can especially slide on ice efficiently. Otters can move large distances in a day, but most often travel only 2 to 3 miles in a day in search of food. Otters do not migrate but stay year round in the refuge.

Male river otters often have 2 or more female partners. A female otter is fertile for about 1 month per year. They breed between December through April. Otters utilize delayed implantation whereas after sex the fertilized egg is held in a sort of hibernation until the time is right for birth. The actual gestation after implantation is only about 60 to 64 days. In this way, it can be 10-12 months before birth after impregnation occurs. Young are usually born between February and April, the later occurring in areas with restricted winter food supplies. Female otters give birth in a den. They do not make or dig their own dens, but find holes created by other mammals, like badgers, beavers, red fox, or muskrats (all of which are on the refuge.) They line their dens with leaves, grass, moss, bark, and hair. Otters usually have from 3 to 6 pups which are delivered fully furred, blind and toothless. Weaning occurs at 12 weeks, but females (without the help of the males) continue to provide food for their young for almost 3/4 of a year after birth. Physical maturity is reached between 3 and 4 years old.

Otters are known for their playfulness. They can often be seen at the refuge playing chase or wrestling in the water. The young otters play to practice survival as adults. They communicate with each other by smell and sound. The otters mark their surroundings with various secretions that indicate various emotional states, like fear, or anger. They can vocalize and the most frequent sound heard among a group of otters is a low-frequency chuckling. For long distance communication they use a birdlike chirp.

Beside the typical many threats from human populations and encroached eco-systems, the otters are threatened by predators when on land, such as,the bobcat, mountain lion, coyote, gray wolf, black bear and red fox. They have no predators when in the water.

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Facts About North American River Otter

Diet: fish, insects

Size: weighs 11-31 lbs, male: 26 to 47 inches long

Lifespan: 8 to 13 in the wild; 25 years in captivity.

Social Structure: Family, headed by female; move in groups.