The primary habitat requirement for river otters is permanent water with abundant fish or crustacean prey and relatively high water quality. Otters are highly mobile and often move in response to shifting availability of food. Otters are more social than most other mustelids, and they forage both in groups and singly. Groups may consist of a female and her recent young, a group of males, or several mothers and their juveniles. River Otters are active year-round, but they are most active at night and during crepuscular hours. Dens may be under tree roots, in hollow logs or trees, in muskrat lodges or beaver dams, or in abandoned burrows. Otters are known for their playful activity. Often an otter will repeatedly slide down a muddy bank into the water much like a child at a water park.
The diet of North American River Otters reflects their aquatic habits. The largest component of the diet is fish, which are taken in proportion to their availability. Secondary components include crayfish and frogs. Others foods consumed opportunistically include large insects, reptiles, birds, fruits, muskrats, young beaver, and mollusks.
In Kansas, river otters have few natural enemies. Farther south they may be eaten by alligators, and in marine habitats, they fall prey to killer whales. When on land in Kansas, river otters may be preyed upon by Bobcats, Coyotes, Cougars, and dogs. More important, however, is mortality caused by humans: trapping, shooting, roadkills, and inadvertent captures in nets and on set lines. Accidents and diseases also cause deaths.
In Kansas, most mating of river otters takes place in March and April. Females are in heat for 42 to 46 days during which time the males follow scent trails of the females. Copulation may occur in water or on land. True gestation lasts from 61 to 63 days but, because the fertilized egg does not implant in the uterus for 8 months or more, the time between copulation and parturition may reach 10 to 12 months. Litter size usually ranges from 1 to 3. The fully furred but blind and toothless young are cared for by the female (males provide no paternal care). Kits take their first solid food at 9 to 10 weeks and are fully weaned by 12 weeks. Juveniles remain with their mothers for 37 to 38 weeks.