For most of the year, the North American otter is most active from dusk till dawn, but in the winter months, it may be more commonly seen during the day (2). Slow-moving fish, and to a lesser extent amphibians and crustaceans, are this species' favoured fare, but a wide range of other food types feature opportunistically in its diet, including birds, reptiles, molluscs, small mammals, and fruit (1) (2) (3) (7). A quick lunge from a position of ambush is the most commonly employed hunting method, but prolonged chases do sometimes occur (2). In the water, this otter has few natural predators aside from alligators, American crocodiles and killer whales, but on land it is much more vulnerable, with bobcats, cougars, coyotes, dogs and wolves all being potential threats (1) (2).
The social structure of the North American otter is extremely variable, with some animals being solitary, whilst others live in family units comprising an adult female with offspring, or occasionally even in large groups made up solely of adult males (2) (3). Groups of otters typically hunt and travel together, and will also utilise the same den and resting sites (2). Dens are made in riverside burrows, under rocks or vegetation near water, in hollow trees or undercut banks, or even in beaver and muskrat lodges (2) (6). There is considerable overlap in individual home ranges, and although this otter is non-territorial, scent-marking with faeces, urine and scent glands is an important form of communication (2) (7). Various vocalisations are also used to communicate, with the most common sound heard amongst a group of otters being a low frequency 'chuckling', while explosive snorts are often used to signal potential danger (2) (3).
Breeding takes place once a year around late winter and spring. Although the actual gestation period is only 60 to 63 days, there may be a period of delayed implantation for up to 8 months following copulation (2) (3) (7) (8). Up to five cubs are born at a time, with the female alone taking responsibility for parental care (2) (7). The young begin to play when around five to six weeks old, and are weaned at three to four months, but will normally remain with their mother for ten months or more (1) (2) (7). In captivity, North American otters may reach up to 25 years of age, but typically do not live longer than 13 years of age in the wild (1).