The Mighty Mustelids: River Otter

Continuing on with the Mighty Mustelid series, I want to introduce one of my favorite carnivores in Iowa – the river otter. They are much larger than the American Mink, growing up to 3-4 feet long and weighing between 11 to 30 pounds! They have short, stalky legs with clawed webbed feet, and a long, narrow body and tail. River otters have a flattened head with long whiskers that help them detect prey in dark waters.

River otters bodies are built for the water. Their large webbed feet and strong tail helps push them through the water with ease. While swimming under water, they are able to close their nostrils and ears to keep water out. Their body is covered in dense fur that provides warmth and helps make them waterproof. In fact, they have the densest fur out of any animal with as many as a million hairs per square inch! They can contort their body in strange positions which helps them catch fast prey items like fish. They will eat a variety of prey including fish, mussels, crayfish, frogs, birds’ eggs, and even small mammals like muskrats. River otters have a very high metabolism so they need to eat frequently and have been known to use tools, like rocks or golf balls to open up clams and mussels. Their diet is often comprised of so much fish, that their scat has been known to have a glitter shimmer from fish scales and has been said to have a floral scent.

While raising young, otters will often use an abandon underground den made by another animal like a beaver. They generally have a litter with anywhere from one to six pups. The pups are born blind and helpless so they depend on their parents to care for them. Pups learn how to swim at two months old. The mother will push the pups out of the den, into the water where they instinctively learn how to swim. Otter family ties are very strong, staying in family groups until they are mature. They are one of the few mammals that have been commonly documented playing throughout adulthood. River otters play in many different forms such as mud sliding, tail chasing and water play to name a few. These group interactions are believed to help learn survival skills and hunting techniques for young otters.

While river otters populations are stable here in Iowa, it hasn’t always been that way. They were once listed as threatened because the river otters were trapped extensively for their pelts. Their pelts were considered fashionable and fancy and were used for hats, gloves, coats, ties, and belts to name a few. Overharvesting, water pollution and habitat loss decimated the river otter populations in Iowa, but reintroduction efforts began in 1985 to reestablish their populations. Since then, their numbers are steadily increasing and are no longer threatened.

Stay curious and happy hiking!