Mink a key species in marsh management
Sometimes wildlife seems as curious about people as we are about them. I often spot deer watching me from the edge of the woods. When I see a fox, it's usually watching me from a thicket of dense vegetation.
Once I was fishing and, between catching fish and watching a belted kingfisher patrol up and down the stream, my eyes did not wander. When I took a break, I noticed a mink on the opposite bank watching me intently. I don't know how long it had been there, but when our eyes met, the mink bolted downstream. Its size (almost 2 feet long), long tubular body, short legs, dark chestnut pelage, and loping gait told me it was a mink. Eventually it disappeared into a maze of roots under a giant sycamore.
Another time I was sitting on a stone bridge in southeastern Pennsylvania. As I lifted my head to see a screaming red-tailed hawk overhead, a linear form caught my eye on the road at my feet. A mink was watching me. Again, as soon as our eyes met, it took off in that distinctive back-bending gait.
I doubt that in either case the mink was actually watching me. It was more likely a coincidence that we caught each other in mid-glance. But often that's all we get with wildlife, especially species that are primarily nocturnal and secretive.
Mink are probably more common than they appear based upon casual observations. Members of the weasel family, they are near-perfect predators and eat almost anything they can catch. They live near water, so fish, crayfish, frogs, snakes, and turtles are favorite prey.
They also eat a variety of rodents, including much larger muskrats, which they kill with a vicious bite to the back of the skull. When muskrats are abundant, mink often use abandoned muskrat lodges as dens.
The predator-prey relationship between mink and muskrats is crucial to marshes. No animal is more important to a marsh than the muskrat. The collective appetite of the entire muskrat population determines how much of the marsh remains open water and how much becomes overgrown with cattails, bulrushes, and water lilies. Muskrats eat these and other aquatic plants.
When the muskrat population is low, aquatic plants flourish and take over the marsh. Open water disappears. When muskrat populations rebound and climb, they reduce the abundance of aquatic plants and create more open water.
More muskrats eat more food. Soon there's not enough food to feed all the muskrats so the population declines. Mink compound the situation by eating the abundant muskrats. When the muskrat population bottoms out, aquatic vegetation rebounds. The increased food supply triggers a population rebound among the muskrats. Then the mink population follows. More muskrats eat more food ... and more mink eat more muskrats. ... And so it goes.
The consequences of all this extend far beyond mink, muskrats and aquatic plants. Marshes act as natural sponges that prevent flooding and filter pollutants from surface water to make it safe for human use. (Those are just a few reasons why conservationists promote wetland conservation.)
When a muskrat population explodes, it can denude a marsh quickly. A denuded marsh becomes a stagnant mud hole with little filtering and water-holding ability. Consequently the quality of surface water suffers. Muskrats affect people.
The open water muskrats create and maintain attracts shorebirds, wading birds, ducks, and many species of songbirds. The aquatic vegetation that remains provides cover for fish, broods of ducklings and adult ducks rendered flightless by their annual molt. Some ducks and geese build their nests on top of muskrat houses. Muskrats affect other wildlife.
If only there was a way to manipulate muskrat populations so a marsh could be stabilized to consist of about half open water and half vegetation. Such a tool exists. It's called predation. And mink are a key predator that regulates muskrat populations. Absent predators, trapping is another tool wildlife agencies use to manipulate muskrat and mink populations, and thus manage marshes.