River Otter

The Basics

The North American river otter (Lontra canadensis), also called the Canadian otter, is the most abundant species of otter. They are found throughout most of North America – from the Rio Grande in Northern Mexico to Canada and Alaska. They live in riparian zones, which are the areas that border stream, rivers, and lakes. Their habitats can be both marine and freshwater.

River otters have brown or grey fur on top with a lighter underside. They have dense short underfur, which is covered by darker, coarse hairs that help to repel water. These otters have muscular and streamlined bodies, short legs, and webbed feet with non-retractable claws. They have small heads, with long necks and shoulders. River otters also have flattened, muscular tails, which make up approximately 40% of the otter’s total body length.

Due to their webbed feet and muscular tails, it comes as no surprise that river otters are excellent swimmers. Their webbed feet and muscular tail help them to move quickly through the water. As they dive underwater, they close their ears and nostrils to keep water out. They can stay underwater for up to four minutes.

North American river otters tend to live alone or in pairs. Their home range can be as large as 30 square miles (78 square kilometers), but usually, their territory is much smaller, between 3 and 15 square miles (4.8 to 24 square kilometers). They mark their territory by urinating, defecating, scratching, and rubbing their scent glands on rocks and trees. Their home range shrinks during breeding and rearing season. Although they live alone or in pairs, these otters often socialize in groups and are known for their playful behavior. This playful behavior is not only social but teaches otters several survival skills. These skills include hunting and fighting.

River otters are nocturnal hunters. They eat mostly aquatic organisms such as frogs, fish, turtles, insects, and some small mammals. They generally forage in the water, but they can also hunt on land. Sometimes river otters will travel between 10 and 18 miles (16 and 29 km) in search of food. They hunt either alone or in pairs.

River otters make dens along the water in empty holes or abandoned burrows. The dens have entrances underwater so that they can be reached from the water. They breed in late winter to early spring, and the females give birth to between one and three pups. The pups are blind and helpless when born. The female is responsible for rearing the pups. After two months, the pups learn to swim. The female gives them a helping hand by pushing them from the den into the water! The pups are quick to learn, though, and are happily swimming in no time.

River otters are prey for bobcats, alligators, coyotes, raptors, and other large predators. They are also threatened by habitat loss and pollution that has occurred since European’s colonized North America. Several groups have been set up to try to help conserve natural populations.

Fun Facts about River Otters

River otters are underwater acrobats that are known for their social and playful behavior and have been observed sliding down slippery slopes for fun. The aquatic mammals have several biological adaptations that have enabled them to inhabit several environments successfully. Let’s take a closer look.

River otters are found in a variety of habitats that range from temperate to very cold. Animals lose heat much more rapidly in water than they do on land. Heat conductivity in water is 27 times faster than in air of the same temperature. This means that even in warm water, aquatic mammals lose heat quickly.

One way that otters can counteract this is by having higher metabolic rates than land mammals of a similar size. A higher metabolic rate enables them to generate more body heat. A river otter’s metabolic rate is approximately 50% higher than a similarly sized land mammal’s. The higher metabolic rate means that the river otters must take in more calories, which is why they are regularly eating.

Embryo Diapause

River otters have an amazing physiological adaptation that may help their young to survive. Otters mate in the early spring months, but embryos remain dormant and free-floating in the uterus for another eight to nine months before they attach to the uterus and begin to develop. This delayed implantation is called embryo diapause and may occur so that the female does not have to raise young during the winter months. Instead, the cubs or pups are usually born the following March after a gestation period of around 60 days.

This biological strategy is found in several animals, where the embryo will not implant and develop until conditions are favorable. Bears, armadillos, and seals are just some examples of animals that use this strategy. Bears, for instance, will breed in the late spring or early summer. The female will then spend all her time hunting to increase her body fat. If her body fat is high enough when she retreats to her den, the eggs implant. Embryo diapause is a way of protecting the embryos, and likely the mothers, survival.

Scent Communication

River otters use their scent to mark their territorial boundaries. They have scent glands at the base of their tail, and they deposit their musky scent on their dung, which is called spraint.

The otters deposit their spraint evenly throughout an otter’s range. Spraint is deposited in less visible areas such as at the base of tree trunks and on boulders. Spraint deposits are usually spread out around 131 – 230 ft (40 to 70 meters) apart. Each otter’s scent is as unique as a fingerprint and can tell other otters information such as the identity, age, sex, and breeding condition of the otter that left it. Otters spend a lot of time exploring the spraint of others.

Dung is used by many animals to mark their territory. For example, rabbits, the West African Civet, and the hippopotamus all use dung as territorial marker posts. Male hippos even use their tail to distribute their excrement as a kind of muck-spreader!