Nutria, River rat

Myocastor coypus
Population size
Life Span
6-10 yrs
4-9 kg
40-60 cm

Coypu, otherwise known as Nutria or River rat, is a large, semi-aquatic rodent. In spite of being a separate species, the animal is sometimes mistaken for a beaver or otter. These rodents are 'a boon and a bane', in a sense that they are both beneficial and detrimental. Thus, endemic to South America, these animals were introduced to the British Isles in the late 1940s. Since then, they have been farmed, playing an important role in the fur industry due to the rich and soft under-layer of their fur. In the meantime, they have destroyed thousands of acres of marshlands. Nowadays, their coat continues to be used in fur industry, though this species is notorious as pest.


Native to South America, this species occurs from middle Bolivia and southern Brazil to Tierra del Fuego. Coypus are also found in Europe, Asia and North America as a result of numerous escapes and liberations from fur farms. Coypus generally inhabit lowland areas with presence of fresh water. However, populations in the Andes live at heights of up to 1,190 meters, while those in the Chonos Archipelago (Chile) may inhabit brackish and salt waters. Preferred habitats include marshes, lake edges and sluggish streams. These animals are most commonly found along banks with emergent or abundant vegetation.

Climate zones

Habits and Lifestyle

Coypus are highly sociable animals, forming family groups of 2 - 13 individuals, usually consisting of an adult male and multiple related females with their young. Young adult males can sometimes be solitary. These animals are neither migratory nor nomadic. They live in the same area throughout their lives. As semi-aquatic animals, coypus are able to remain underwater for over 10 minutes at a time. This species is nocturnal. Period of increased activity occurs at night, when animals swim, feed and groom. Feeding and grooming takes place in special platforms, which they construct out of vegetation. They also make burrows, where they find shelter. These dens may be either simple tunnels or a tunnel system, consisting of multiple long passages of over 15 meters as well as nesting chambers. These animals are also known to make paths through the grass, travelling around their dens within a radius of 180 meters.

Diet and Nutrition

These herbivorous animals mainly feed upon stems, leaves, roots, bark and other aquatic vegetation, supplementing their diet with floating objects such as logs.

Mating Habits

127-139 days
3-6 kits
7-8 weeks

Coypus are through to have a polygynous mating system, where pairs disperse right after mating. These highly productive animals mate at any time of year. Gestation period lasts for 127 - 139 days, yielding a litter of up to 13 young with an average of 3 - 6. After giving birth, the female may mate again. Thus, she is able to produce young 3 times per year. Offspring of this species are born with their fur and open eyes. The joeys feed upon maternal milk for 7 - 8 weeks before they leave their mother. Females reach sexual maturity at 3 months old, whereas males are mature a bit later - at 4 months of age. Sometimes the age of sexual maturity may delay to up to 9 months old.


Population threats

Currently, there are no notable threats to the population of Coypus.

Population number

According to IUCN, the Coypu is widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC), but its numbers are decreasing.

Ecological niche

Consuming aquatic vegetation, these animals play an important role in the wetland ecosystem of their range. However, coypus negatively affect the ecosystem through several ways. Thus, they destroy reed swamp areas as well as eliminate certain plants from their range. In some areas, these animals are considered pest species due to attacking cultivated crops such as rice and damaging dikes and irrigation facilities with their burrows. In addition, coypus destroy nests and collect eggs of some aquatic birds, including these of endangered species.

Fun Facts for Kids

  • In France, Coypu is known as ‘ragondin’.
  • When diving, these accomplished swimmers are able to remain submerged for up to 5 minutes.
  • Coypus are active during the nighttime hours, when they play and socialize with conspecifics.
  • The coat of coypus consists of under-layer and outer layer: the first is composed of shaggy, yellow or brown hairs, whereas the second is made up of fine, grey colored fur, which was trendy in fashion industry a couple of decades ago.
  • The long incisors of this animal are yellow to orange or orange to red.
  • When coypu dives, special flaps in its mouth and nose close, keeping the water from entering its stomach and lungs.


1. Coypu Wikipedia article -
2. Coypu on The IUCN Red List site -

More Fascinating Animals to Learn About