The muskrat (Ondatra zibethicus) is an exceptionally aquatic rodent, spending the majority of its life in and around water. Native to North America, their extensive range covers wetlands across the continent. Muskrats are often found in marshes, ponds, and slow-moving streams, confirming their dependence on a watery environment.
Physical Features Tailored for Water
The muskrat’s success in water stems from several unique morphological features. Its dense fur is structured with two layers: a soft, insulating undercoat and a layer of longer, coarse guard hairs that remain virtually waterproof. This dual-layered coat traps a layer of air against the skin, offering both buoyancy and thermal protection in cold water.
Propulsion is primarily achieved by the large, partially webbed hind feet, which act as paddle-like structures. The front feet are smaller and used mostly for digging and handling food. The muskrat’s tail is a distinguishing feature, being long, nearly hairless, and laterally flattened. This rudder-like tail is snaked back and forth to maintain directional stability while the animal swims.
Diving Ability and Underwater Performance
Muskrats possess physiological capabilities that allow for extended underwater performance. They can remain submerged for 12 to 17 minutes, with some individuals staying underwater for up to 20 minutes. This endurance is supported by a specialized “dive response” that significantly slows the heart rate when submerged.
Their physiology is less sensitive to the buildup of carbon dioxide in the blood compared to many other terrestrial mammals, which helps prolong their dive time. When diving, the ears and nostrils automatically close to keep water out. A unique lip structure seals behind the protruding incisor teeth, allowing the muskrat to gnaw on aquatic vegetation while its mouth is completely closed underwater. This adaptation permits them to forage effectively for roots and stems without having to surface for air. Muskrats are agile swimmers, capable of moving up to three miles per hour and maneuvering backward through submerged tunnels.
Aquatic Housing and Territory
The muskrat’s dependence on water shapes its choice of habitat and shelter construction. They prefer wetland areas where the water depth is sufficient to prevent freezing solid in winter, ensuring access to food and shelter year-round. These rodents construct two main types of homes, depending on the environment.
In areas with stable banks, muskrats excavate bank burrows with entrances located well below the water line. If suitable banks are unavailable, they will build dome-shaped lodges. These lodges are constructed from piled vegetation, like cattails and mud, rising above the water’s surface. Water serves as a primary defense mechanism, as the underwater entrances to their homes provide effective protection from most land-based predators.