River Otter
- Physical Appearance: The river otter is long, cylindrical, and muscular with a short, stout neck that is nearly the same diameter as the broadly flattened head. Adults weigh between 11 and 33 pounds and range from 35 to 54 inches in total length. Males are generally about 25% heavier than females. The pelage is made up of short, soft, dense under-fur that is protected by longer, stiff guard hairs. The coloration is a rich, glossy shade of brown but may be black or even blonde. Typically, the fur is lighter colored on the cheeks, throat, and belly.
- Range: The river otter is found throughout most of North America.
- Habitat: River otters live in and along lakes, wetlands, rivers, and streams, exploiting a variety of aquatic habitats. They thrive in mountainous and coastal regions and may be found in both freshwater and marine environments. River otters do not construct their own dens but instead rely on logjams, beaver lodges, the bank dens of beaver and muskrat, and natural features, such as cavities in tree roots, undercut banks, and fallen timber, for their den sites. The river otter prefers habitat where dense riparian vegetation is present adjacent to water, relying on the escape and resting cover provided.
- Food Habits: The river otter is primarily carnivorous and, like most other predators, has teeth especially adapted to grasping, cutting, and shearing. Consuming a wide variety of prey, river otters are keen hunters. River otters are specialists at catching fish, which are their preferred food source although the diet varies seasonally and regionally. Crustaceans (crayfish and crabs) may be a very important component of the diet in regions where they occur and may compose 100% of the diet at certain times of the year. Amphibians, reptiles, birds (shorebirds and waterfowl), insects, and even mammals, such as muskrat and beaver, may occasionally also be consumed by river otters.
- Reproduction: The breeding season for river otters occurs in late winter to early spring with March and April being the peak months. The gestation period is between 290 to 380 days with young typically being born in late winter to early spring. River otters produce only one litter per year with an average litter size of two to four young. Females may successfully breed beginning in their first year, but males are typically not successful breeders until they are at least three years old or older. Pups are born toothless and blind in a den that is usually a subterranean burrow. After being born, pups emerge from the den at about two months of age and are fit to leave the birthing area by three months. The young remain with the female in a family unit until seven to eight months of age, or just prior to the birth of a new litter. The rearing of young is left solely to the female. The siblings may remain together until 12 to 13 months of age, at which time they normally disperse. River otters can live for more than 20 years, but the typical life span is likely less than 10 years in the wild.