The muskrat, Ondatra zibethicus, is a semi-aquatic rodent common throughout North America. Weighing between one and four pounds, this mammal is well-adapted to cold climates. Muskrats do not hibernate; instead, they remain active year-round, relying on a combination of behavioral and physical traits to endure freezing temperatures.
Muskrat Winter Activity
Muskrats remain active throughout the winter, which contrasts sharply with true hibernation. Hibernation involves a voluntary, extended state of metabolic depression where an animal’s body temperature and heart rate slow dramatically, allowing them to subsist entirely on stored body fat. Muskrats, however, are constantly foraging for food, which requires them to maintain a relatively high metabolic rate.
While they do not hibernate, muskrats may enter periods of torpor, a shallower state of reduced physiological activity. Torpor is a temporary, involuntary drop in body temperature and metabolism that can last for hours, triggered by extreme cold or lack of calories. This short-term energy conservation allows the muskrat to survive temporary, harsh conditions. The ability to quickly rouse from this state is important for an animal that must regularly return to the water to eat.
Winter Survival Strategies
Survival for an active muskrat depends heavily on the insulated structures they construct and maintain in their aquatic environment. They build dome-shaped lodges, often three feet or more in diameter, using materials like cattail stalks and mud. These lodges are entered from beneath the waterline, providing a dry, protected chamber above the water that is safe from both predators and the elements.
To extend their foraging range under the ice, muskrats create smaller, temporary structures called “push-ups.” A muskrat chews a hole through the thin ice and then piles mud and vegetation around the opening to form a small, insulated dome. These push-ups serve as hidden feeding stations and breathing holes, allowing the muskrat to rest and consume food. The muskrat must continuously forage for aquatic vegetation, such as the roots and stems of cattails, as they do not store food in their lodges like beavers.
Physical Adaptations for Cold Water
The muskrat possesses several physical traits suited for remaining submerged in cold water for extended periods. Their coat consists of two layers: a dense, soft underfur that traps a layer of insulating air against the skin and a layer of longer, water-repellent guard hairs.
This specialized fur allows them to maintain their body temperature while swimming in freezing water. Muskrats are skilled swimmers, propelled primarily by their large, partially webbed hind feet. Their long, vertically flattened tail, which is scaly and nearly hairless, acts as a rudder and a secondary means of propulsion.
The animals can also hold their breath for a significant amount of time, with dives lasting anywhere from 10 to 17 minutes, enabling long underwater foraging trips. Muskrats regulate blood flow to their less-insulated extremities, such as their feet and tail, a process called regional heterothermia, which keeps their core body temperature stable while minimizing heat loss.