As there have been so few observations of the hairy-nosed otter in the wild, very little is known of its biology. However, this elusive species has been photographed early in the morning and late in the afternoon, and also been observed to be active at night (5). Fish and water snakes are the preferred prey of this otter, although it may supplement this diet with a variety of frogs, lizards, turtles, crabs, small mammals and insects (1). The most commonly employed hunting method is believed to be a quick lunge at speed that startles its prey and traps it in the roots of a semi-submerged tree, although this stealthy predator is also known to steal from fishing nets (5). In the water, the hairy-nosed otter has few natural predators, aside from pythons, and the Siamese crocodile (Crocodylus siamensis) in Tonle Sap Lake. On land, however, it may fall prey to feral dogs, and its cubs in particular may be taken by large birds of prey, such as the grey-headed fish eagle (Ichthyopaga ichthyaetus) (5).
Although many otters are highly social animals and often live in small family groups, the hairy-nosed otter is thought to be a largely solitary species, like its cousin the Eurasian otter (Lutra lutra). However, groups of up to six otters have been seen, and it is possible that small family units of parents with their cubs form after the breeding season. The timing of this is not fully understood, but is thought that cubs are born from December through to February after a two month gestation period (1) (5).
Scent marking with faeces, urine and scent glands is an extremely important form of communication amongst otters. Fishy, musky smelling spraints are typically placed on exposed logs or branches in the water to inform other otters of the boundaries of foraging sites (2) (12). Various vocalisations are also used to communicate, with the most commonly heard sound of the hairy-nosed otter being a single syllabic chirp, while chatters are also used by mothers to their cubs (5).