Biology Of Muskrats
Muskrats can reach a body length of 12.6 in (32 cm), plus a long tail 11.8 in (30 cm) and a weight of about 3.3 lb (1.5 kg), although most animals are typically about 2.4 lb (1.1 kg) in weight. The waterproof fur (pelage) of muskrats is composed of a dense underfur, important for insulation, and a lager of longer, usually dark-brown, protective guard hairs.
Muskrats of both sexes have a pair of large glands near their anus, which enlarge during the breeding season, and produce a strongly scented chemical called musk, from which the common name of these animals is derived. Musk is used in the manufacture of perfumes, although it is not commonly harvested from muskrats for this purpose.
Muskrats are excellent swimmers, using their partially webbed feet which are fringed with stiff hairs that broaden the propulsive surface. The hairless, scaly tail is flattened, and is used as a rudder during swimming. Muskrats can remain submerged for as long as seventeen minutes, and they often do this to hide, when they feel threatened by a predator.
Muskrats mostly eat aquatic and riparian plants of various sorts, and they sometimes forage on land, occasionally in farmers' fields. Muskrats also eat mussels, fish, and other aquatic animals. Most feeding is done at night, dawn, or dusk, but muskrats are sometimes seen during the day.
Muskrats are found in marshes, swamps, and other types of static, open-water wetlands, where they build family houses made of mounds of piled-up reeds and cattails plastered with mud. These structures are typically more than one meter high and several meters broad. Into these mounds the muskrats construct a tunnel with an underwater access hole, leading to an internal den with a grassy bed. Muskrats also live along streams and rivers, where their dens are dug into earthen banks above the high-water level, with the access hole located under low-water and below the limit of freezing in winter. Muskrat houses and diggings are often destroyed during spring floods, and are not usually repaired; the muskrat will instead construct a new accommodation.
In optimal habitats such as reedy marshes, muskrat population densities can reach 85 animals per hectare. Sometimes, excessively large muskrat populations can degrade the local habitat, forcing a population crash until the vegetation recovers.
Muskrats are very fecund, and can produce several litters each year. They live in family units in mud lodges in territories, which they actively defend from incursions by other muskrats. During the spring, dominant females take possession of the best habitat and drive away younger females and males. Much strife occurs at this time, and some animals are killed during the fighting, and those that are driven away are often killed by predators.