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River otters live in freshwater and coastal marine habitats such as rivers, marshes and lakes all over the United States. In the wild, river otters live up to eight or nine years. Since they are semiaquatic mammals, river otters spend time both on land and in water. To function in a dual environment, river otters have evolved several important adaptations that help them to thrive.
River otters have waterproof, velvety coats that act as insulation. A layer of fat sits below the slick coat, providing the otters with added insulation. These semiaquatic mammals also developed fur on the bottoms of their feet, which provides them with warmth and better traction. River otters also have long whiskers that help them search for food and avoid obstacles while swimming underwater.
Swimming and Diving
To travel better in water, river otters developed adaptations such as four webbed feet and a propeller-like tail. These features enable river otters to swim up to 9 miles per hour. While diving, river otters can slow down their heart rate to sustain oxygen. River otters can also close their ears and nostrils using valve-like flaps to keep water out while swimming and diving. According to SeaWorld, diving river otters are able to hold their breath for up to 8 minutes before they need to resurface.
Traveling on Land
When river otters are not playing or swimming in water in search of food, they spend a lot of time on land grooming and resting. When traveling on land between waterways -- especially during the winter when water solidifies into ice -- river otters depend on their feet pads to provide traction when running or sliding. River otters are able to travel on land at speeds of up to 29 miles per hour, according to SeaWorld. Their ability to travel quickly on land is essential for escaping predators, such as alligators and coyotes, who might consider an otter a tasty snack.
Thermoregulation and Metabolic Rate
River otters have a fast metabolic rate -- almost 50 percent faster than similar-sized land mammals, according to SeaWorld. This is important because river otters lose heat quickly in water, so they must constantly burn energy to replace lost heat. A fast metabolic rate requires river otters to eat frequently during the day. The river otters' fur and layer of fat underneath their fur assists in slowing heat loss while swimming.
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