The North American river otter (Lontra canadensis) and the muskrat (Ondatra zibethicus) are common semi-aquatic mammals that share the same freshwater and coastal marsh habitats across much of North America. Both species are highly adapted to life in and around water, often utilizing the same riverbanks, wetland areas, and riparian zones for shelter and foraging. This close proximity naturally leads to interactions, raising the question of whether the otter views the muskrat as a competitor or as a potential meal. This article explores the predator-prey relationship between the agile otter and the herbivorous muskrat.
The Primary Components of the Otter Diet
River otters are classified as opportunistic carnivores, meaning their diet is shaped primarily by the seasonal availability and vulnerability of prey species. The overwhelming majority of an otter’s caloric intake comes from aquatic organisms, making them largely piscivorous, or fish-eaters. Fish remains are found in nearly all otter scat samples, often accounting for well over 80% of the diet.
Otters tend to prefer slower-moving, non-game fish species like suckers, catfish, and perch, as these require less energy to catch. Crustaceans, such as crayfish and crabs, represent the second most important food source for otters, especially where they are abundant. In some regions, crustaceans may even temporarily exceed fish in frequency of consumption.
Other secondary prey items include amphibians like frogs and salamanders, as well as reptiles such as small turtles. Aquatic insects and mollusks are also eaten when they are readily accessible. This standard menu establishes the baseline for the otter’s food selection, highlighting a clear preference for aquatic life that can be easily captured.
Muskrat Consumption: Frequency and Circumstance
While the bulk of an otter’s diet is aquatic, muskrats are a documented food item, though they are considered a secondary or tertiary prey source. Studies analyzing otter digestive contents consistently show that mammalian prey, including muskrats, makes up a relatively small percentage of the total diet. Mammalian remnants are present in less than 7% of otter scat samples.
Muskrat predation often becomes more frequent under specific circumstances. A scarcity of preferred aquatic prey, perhaps due to drought or seasonal changes, increases the likelihood of an otter targeting a muskrat. During winter, when fish are less active and harder to locate, the relatively sedentary muskrat may become a more viable, high-calorie food option.
Otters are also more likely to target vulnerable muskrats, such as young kits or adults that are injured or sick. The caloric benefit of successfully catching a small mammal must outweigh the energy expenditure of the hunt. An adult muskrat, weighing between two and four pounds, offers a substantial energy return compared to a small fish.
Predatory Tactics and Habitat Overlap
The shared habitat of rivers, marshes, and wetlands provides the necessary conditions for otter-muskrat encounters. Muskrats construct both bank burrows and dome-shaped lodges from vegetation, and these structures are often situated directly in the otter’s foraging territory. The otter is a sleek, powerful swimmer, giving it a significant advantage over the muskrat in the water.
Otters exploit the muskrat’s limited escape options by pursuing them directly in the water, where the otter’s agility and speed are maximized. A key predatory tactic involves the otter’s ability to locate and enter muskrat dwellings. Otters are known to tear open the roofs of muskrat lodges to access the animals inside.
The otter’s smaller, more elongated body allows it to navigate tunnels and burrows that might be inaccessible to larger predators. By blocking the underwater entrance or pursuing the muskrat into the confines of its home, the otter is able to successfully capture the rodent. This ability to hunt both in the water and within the terrestrial structures makes the otter an effective, opportunistic predator of the muskrat.