Possibly no animal has more of a reputation for its playful nature than the river otter. Groups of otters are sometimes seen splish-splashing and slipping and sliding all around the rivers and riverbanks where they live.
Not too long ago, North American river otters were an incredibly rare sight in Illinois. Their population was hit hard by the fur trade centuries ago and more recently by habitat loss as river habitats were destroyed.
The otters were declared threatened in Illinois in 1977 and then listed as a state endangered species in 1989. In the 1990s, efforts to help their population in Illinois included trapping otters from states with healthy populations and relocating them here. Those efforts were successful, and today river otters live in every county in Illinois. They were removed from the state's endangered species list in 2004.
In 2009, the river otter population in Illinois was estimated at 11,000 and growing. These semiaquatic animals live along rivers, and they are most populous along the Mississippi River and along the rivers in the northwestern part of the state.
Grow your knowledge of these animals with these five facts.
They are entirely different than sea otters
Because people are not as familiar with river otters as they are with other semiaquatic animals like beavers and muskrats, river otters are often confused with sea otters. River otters live in both freshwater and saltwater habitats, so confusion between the two animals often occurs in coastal areas. However, there are some big differences between the two animals.
Words to know
Semiaquatic: Living both on land and in water
Metabolic rate: The amount of energy used by an animal while at rest
Nictitating membrane: A transparent third eyelid in some animals that protects the eye while maintaining vision
First, sea otters are much larger than river otters — about two to three times bigger. They also swim differently. Sea otters typically float on their backs, while river otters swim with their bellies facing down. Their tails are different too. While river otters have long, pointed tails, sea otters have short, flat tails.
They are built for swimming
Like other semiaquatic animals, river otters are built to swim. They have short legs and webbed feet that help them swim faster, and their long, narrow bodies, flat heads and long, strong tails help them maneuver in the water. They even have eyes and ears toward the top of their heads to help them when swimming at the water's surface. Their short, thick fur helps keep them warm while in cold water.
River otters can stay underwater for as long as eight minutes at a time, and their ears and nostrils close when they are submerged. They have an extra eyelid, called a nictitating membrane, that protects their eyes and allows them to see underwater. They are fast swimmers, traveling through the water at speeds of up to 8 mph. They can also dive up to 36 feet deep.
They are land lovers too
We think of river otters as aquatic animals, but they actually spend most of their time on land. They use water mostly to hunt for food and travel through their home range. This is another difference between river otters and sea otters. Sea otters spend almost all their time in water.
Because river otters spend so much time out of water, they get around pretty well on land. They can even run at speeds of up to 15 miles per hour. They also use slippery terrain, like muddy or snow-covered areas, to slip and slide across land more quickly.
All that play serves a purpose
River otters typically live alone or in pairs, but they often gather in social groups, and these groupings of otters are known for their playful behavior. In addition, young river otters, called pups, often remain with their mothers for many months, and during that time play is a normal part of their development.
Groups of otters are often seen slipping and sliding over muddy or snowy ground and ending with a splash into the water or further play around the water. This may look like pure fun, but all that play is beneficial too. These playful behaviors help the otters learn important survival skills such as hunting techniques, how to mark their territory with their scent and how to develop social bonds.
Although otters are naturals in water, they aren't born knowing how to swim. When they are about two months old, mother otters will push their pups into the water and watch them carefully until they are able to swim on their own.
They are big eaters
Otters eat a lot each day out of necessity. Because mammals lose body heat in the water much more quickly than they do on land, they have higher metabolic rates than animals that live on land. In fact, the metabolic rate of a river otter is about 50% higher than that of a land animal of a similar size. Sea otters have metabolic rates as much as 25 times higher than land-based animals of the same size.
Their higher metabolic rates mean they need to eat more calories each day. In the case of river otters, they mainly eat other animals, including crayfish, fish, frogs, turtles and other invertebrates. In the water, otters use their whiskers to help them find prey they can't otherwise see. They will also sometimes eat small animals from land and occasionally aquatic plants as well.
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