Muskrat

## Description

The muskrat (Ondatra zibethicus) is a medium-sized semiaquatic rodent native to North America. It lives in wetlands over a wide range of climates and habitats. It has important effects on the ecology of wetlands and is a resource of food and fur for humans. The muskrat is the largest species in the subfamily Arvicolinae, which includes 142 other species of rodents, mostly voles, and lemmings. Muskrats are referred to as "rats" in a general sense because they are medium-sized rodents with an adaptable lifestyle and an omnivorous diet. They are not, however, members of the genus Rattus. They are not closely related to beavers, with which they share habitat and general appearance.

## Appearance

Muskrats are covered with short, thick fur, which is medium to dark brown or black in color, with the belly a bit lighter (countershaded); as the animal ages, it turns partly gray. The fur has two layers, which provide protection from cold water. They have long tails covered with scales rather than hair. To aid in swimming, their tails are slightly flattened vertically, a shape that is unique to them. When they walk on land, their tails drag on the ground, which makes their tracks easy to recognize. Muskrats can close off their ears to keep water out. Their hind feet are webbed and are their main means of propulsion. Their tail functions as a rudder, controlling the direction they swim in.

## Distribution

Muskrats are found in North America and Eurasia. North American population occurs from the northern parts of the continent southwards to the Gulf coast, reaching the Mexican border. They mostly inhabit wetlands, areas in or near saline and freshwater wetlands, rivers, lakes, streams, or ponds.

## Behavior

Muskrats live in large social units, which are family groups. Each group has its own home range. Sometimes, when the territory is too small for the group, females will drive their young away. However, even in cases if fighting and cannibalism take place, the group doesn't disperse but remains united. Muskrat families build nests to protect themselves and their young from cold and predators. In streams, ponds, or lakes, muskrats burrow into the bank with an underwater entrance. These entrances are 6-8 in (15-20 cm) wide. In marshes, push-ups are constructed from vegetation and mud. These push-ups are up to 3 ft (91 cm) in height. In snowy areas, they keep the openings to their push-ups closed by plugging them with vegetation, which they replace every day. Some muskrat push-ups are swept away in spring floods and have to be replaced each year. These rodents are most active at night or near dawn and dusk. Although slow on land, muskrats are known to be excellent swimmers. Moreover, when diving, they are capable of remaining submerged for as long as 12-17 minutes at a time. They use musk as the primary form of communication as well as a warning to outsiders. Muskrats also associate through vocalizations, including squeaks and squeals. Quick temperature changes, combined with dry and hot weather negatively affect these animals.

## Diet

Muskrats are primarily herbivorous. Their diet generally consists of cattails, sedges, rushes, water lilies, pondweeds, and other aquatic vegetation. Depending on geographical location, muskrats may also consume occasional clams, mussels, snails, crayfish, small fish, and frogs.

## Reproduction

Muskrats are polygynandrous (promiscuous) animals: this is when both males and females have multiple mates. Muskrats mate between March and August. During the mating season, males compete for their mating rights. The gestation period lasts for less than a month, yielding 5-10 young. Females may produce up to 3 litters per season, usually every month. Although newborn muskrats are blind, helpless, and lack fur, they grow up very quickly. By one week old, their skin exhibits thin fur. By 2 weeks old, the young open their eyes. Muskrats begin venturing from the den at 2-3 weeks old, typically taking short trips before returning to the den. They are weaned at 3 weeks old, and gaining independence at 6 weeks old. The age of reproductive maturity is 1 year old.

## Population

### Population threats

Most of the threats to the muskrats' population have to do with human activities. These animals are commonly trapped for their pelts that have high commercial value worldwide. In areas where these rodents are abundant, they negatively affect the environment, often causing habitat destruction. Thus, due to their burrowing habits, muskrats occasionally damage river banks. Furthermore, because of over-consumption, they reduce the amount of aquatic vegetation. For these and other reasons, muskrats are hunted and poisoned throughout their range as a pest species.

### Population number

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

### Ecological niche

Muskrats are a key prey species for local predators. In addition, their populations naturally cycle; in areas where they become abundant, muskrats are capable of removing much of the vegetation in wetlands. They are thought to play a major role in determining the vegetation of prairie wetlands in particular. They also selectively remove preferred plant species, thereby changing the abundance of plant species in many kinds of wetlands. Muskrats also build feeding platforms in wetlands; they help maintain open areas in marshes, which helps to provide habitat for aquatic birds.

## Fun Facts

Due to so-called 'regional heterothermia' - a special adaptation that regulates the blood flow to their limbs and tail - these parts of their body usually remain cooler than the core of the body.

As accomplished swimmers, muskrats are capable of swimming not only forwards, but also backward.

Finding food, the muskrat will not consume it right on the spot. Instead, the animal will carry its meal to a special feeding spot, located either in the water or near one of its daily routes. Muskrats usually leave a pile of shells known as "midden."

One of the most distinctive features of the muskrat, for which the animal is actually named, is its musk. Below its tail, this rodent has 2 scent glands, which emit the characteristic scent. This odor serves as a form of communication, informing conspecifics of nearby threats.

As opposed to the closely related beaver, the muskrat doesn't collect winter food supply, since this animal consumes only fresh plants. During the winter, the rodent survives due to digging through the mud to come out of its den and get to plants, located under the layer of ice.

During the cold winter months, muskrats often huddle together in groups to conserve heat in their lodges.

Consuming cattails, otherwise known as an "eat-out", groups of muskrats are able to open up areas of shallow water, thus creating suitable conditions for certain water plants as well as shelters for water birds.