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An Illinois River Almanac

Jason Haupt's Energy and Environment Blog
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Animal of the Week: River Otter

Everyone loves a comeback story, and going from nearly extirpated in Illinois and on the state endangered species list to being delisted in 2004 is the ultimate comeback story. Fun-loving, playful, and cute are just a few of the descriptions that are used to describe the River Otter. The River Otter is among the most recognizable mammal in Illinois because of its apparent playfulness, and its looks don't hurt either.

The River Otter is highly recognizable with its long body and tapering tail. The tail is long, accounting for as much as one third of its body length, and covered in fur. The River Otter is covered in short thick fur that is dark brown to reddish brown on its back and sides. Its belly is a much lighter brown or grey with a white, tan or silvery throat, cheeks and chin. The River Otter is much larger than any of its close relatives (mink or muskrat), and all of its toes are webbed. The River Otter is the largest aquatic mammal found in Illinois. The River Otter has a streamlined body, waterproof fur, and webbed feet all making the River Otter highly adapted to life in the water. River Otters can be found in much of Alaska and all across Canada and throughout the lower 48 states with the exception of the arid south west.

River Otters are aquatic mammals, and they can be found in nearly all aquatic habitats found in Illinois. They are commonly found in rivers with extensive wet forests or emergent vegetation. This means that they like to be in areas that have lots of water and plenty of cover. River Otters are not highly territorial and multiple territories will overlap, though otters tend to avoid each other. A River Otter's territory is dependent on the type of habitat, and the availability of food and cover. Often the territory is long and narrow extending as much as 50 miles. With such a large territory, the River Otter will concentrate its activities in the areas that provide the best food and cover. As an area becomes less desirable the center of activity will change. During the winter months, River Otters will concentrate activity in areas with access to open water.

River Otters are primarily carnivores. They forage in water and tend to concentrate on fish, crayfish and frogs. River Otters will also eat a wide variety of other prey, including aquatic birds and their eggs, turtles and muscles. They are also known to rarely eat small mammals, berries and aquatic plants. River Otters are primarily foragers using their sensitive whiskers to locate prey under logs, rocks and in sand. They will also ambush prey; however, they rarely participate in prolonged chases preferring to go after slower fish and other prey.

River Otters generally have small litters, usually including two or three pups. Larger litters, up to 6 pups, are possible, but not common. Pups are born between February and April and the female will mate soon after giving birth to its litter. River Otter pups are born covered in fur, but their eyes are closed. The pups begin to eat solid food at eight to ten weeks and are fully weaned at 10 to 12 weeks of age. Pups are taught to hunt by the mother who brings live prey for practice. Families will disband in the fall or winter, though some families will stay together over the winter and disband the following spring.

River Otters have the most durable fur of any North American fur. As a result, they were hunted extensively and were nearly extirpated in Illinois. In the early 1900's they were only found in Southern Illinois. They were protected in the 1920's and were placed on the state endangered list in 1989. In the 1990's the Illinois DNR released a number of River Otters into the many Illinois waterways and in 1999 the River Otter was moved to the state threatened list. The River Otter was removed from the list in 2004. They are still threated by habitat loss and pollutants in the water.

River Otters are at the top of the aquatic food chain and there is a danger of bioaccumulation in River Otters. They have few natural predators, but they will be taken by Bobcats, Coyotes, or Dogs. They are still trapped unintentionally in beaver traps or caught in fish nets; they are also killed by automobiles.

Fun River Otter Facts:

  1. Female River Otters are able to delay implantation for up to 11 months. This means that though development only takes two months, total gestation time can be anywhere from months to just over a year.
  2. Otters swim using one of three methods 1) Undulating in the water 2) Using all four paws to paddle 3) Alternate paddling of the hind paws.
  3. Otters will slide along the ground using their feet to propel them. Otters will also slide on their bellies for what appears to be just for fun.


Field Manual of Illinois Mammals-Joyce E Hofmann.

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