Muskrat populations in North America are declining. But why? For Hakai Magazine, Brandon Keim dives into the reasons why the number of these under-appreciated, semiaquatic rodents are dwindling, to help us understand their contribution to the environment and the others species that share it.
The animals are often mistaken for beavers, another semiaquatic rodent, albeit one whose adults weigh as much as a six-to-eight-year-old child; muskrats tip the scales at a couple kilograms. That lack of appreciation extends to the ecological roles performed by muskrats. Though their influences are subtle when compared with the wetland engineering of beavers, muskrats are still important habitat makers and nutrient movers. They help the world come to life, even if we don’t readily notice them doing so; their diminishment would reverberate far beyond them. It is also foreboding. What does it portend, and what does it say about how humans have transformed the world, when in so many places such a common, hardy animal can no longer thrive?
In his review of muskrat ecosystem impacts, Ahlers describes how these disturbances produce dramatic increases in plant species richness. One study suggested that muskrats were primarily responsible for an increase of more than 70 percent in the variety of plants found in the disturbed areas of a cattail marsh; by grazing on abundant plants that would otherwise become dominant, muskrats also create space for rare plants to grow. Meanwhile, their houses—a meter or more from the water and up to two meters wide, lasting for a year or two before gradually degrading—become habitat features themselves. “Birds are probably the most conspicuous beneficiaries of the muskrat’s influence on wetlands,” writes Ahlers, including the ducks, terns, grebes, and other wetland avians who use muskrat houses as nesting sites. Turtles, water snakes, and frogs also dwell in them, and even skunks and shrews—more than 60 vertebrate species altogether, by one count.
These animals also avail themselves of the reed feeding platforms that muskrats construct. So do beetles and other invertebrates, and in turn their predators benefit. As the platforms decompose, they even increase local microbial diversity. And where muskrats dig dens in banks along the water’s edge rather than build houses, their burrowing aerates riparian soils, and those subterranean chambers become habitat for reptiles and amphibians. “When you remove them,” says Smith of muskrats, “the ecology of the wetland changes.”
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