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Nature Notes: American Mink

If you enjoy this article, you’re sure to love Ed Robinson’s 2018 book, Nature Notes from Maine, which includes many of the wildlife stories on this website, new stories and stunning photographs and ink drawings. Click here for details.

By Ed Robinson

John Boomer photo

John Boomer photo

Most young Millennial women of today would not be caught dead wearing mink, or any other fur, but it wasn’t that long ago that a mink coat or stole was considered the height of fashion.  That’s easy to understand since prime mink fur is some of the most beautiful around, and thanks to selective breeding by fur ranchers since the early 1800s, it is available in a wide range of colors.  Let’s look at the elusive wild mink to see how it fits into the wild kingdom.

The mink is a scrappy survivor, and they have inhabited the Earth for a very long time.  Fossil records of mink go back to the Irvingtonian period of natural history, from 240,000 to 1.8 million years ago.  Those fossils were found throughout North America, and that range still supports native mink populations today with the exception of arid regions of the American Southwest.  Mink are semiaquatic animals who always live near water, and they are heavily dependent upon prey species associated with water, both fresh and saline.

Unless you tend to skulk around rivers and pond edges as I do, it is possible that you have never seen a mink.  They are most active at dusk and dawn, and are able to hunt in full darkness thanks to good eyesight and great hearing.  You might have confused a mink with a large weasel, a small river otter, or even a pine marten if you were near large forested areas.  The mink has a slim, elongated body up to 18 inches in length, with a furry tail that might stretch 10 inches.  A large mink may reach four to five pounds.  Short but powerful legs give the mink a low profile so they can sneak around in cover and get into tight places to find prey.  Mink feet are partially webbed, making this species an adept swimmer, capable of diving to depths over 10 feet.

Mink fur is lush to provide plenty of insulation, especially in winter when the underfur grows deep.  Their normal color is a rich brown, but variants run from tan to gray.  Long guard hairs are bright with natural oils, in darker colors up to black.  Sometimes you will see small white patches on the chin, chest or throat.  Unlike their cousin, the weasel, mink do not turn white in winter.  The ears are small and rounded, and the small, piercing eyes are jet black.  With long sharp canines and powerful jaws, the mink is quite capable of killing prey larger than itself, and can put up a ferocious defense against predators.  Sharp claws also allow the mink to climb trees with ease.

The preferred habitat for mink is along waterways, from the ocean coastline, to rivers, lakes, canals, ponds and streams.  Rocky shorelines, gnarly tree roots, and dense brush or grasses provide ideal hunting territory and protective cover for mink.  Mink are not fast movers, capable of bounding along at speeds up to eight mph in short bursts, but they will cover several miles over a few days in search of food.  Males are very protective of their turf, using their scent glands to mark their grounds and fighting to the death to keep out interlopers.

The mink’s sex life would make for a torrid novella, hot and short.  Over a period of three weeks in late winter, males pursue females aggressively and fight off rivals for the right to breed.  Once a pairing is established, the male can be violent during an extended breeding session.  Promiscuity is the norm, with males and females having multiple partners.  Once mating occurs, the male is on his way, leaving the female to raise her young.  Having worked on a mink farm in New York State during the mating process, I can tell you it is not for the faint of heart.

Once impregnated, the female has the ability to delay implanting the fertilized egg up to six weeks.  This allows her to wait through periods of heavy late winter weather, hoping to increase the chances of survival of her young.  The embryo develops in about 30 days, and the young kits are born blind, totally dependent upon mother’s milk for their first few weeks.  An average litter is four, but as many as 12 have been recorded. Weaning occurs in about five weeks, and the kits can join in the hunt for food after eight weeks.  The young remain with their mother until autumn, when she shoos them off to find their own winter den, and they are ready for breeding the following spring.  Preferred den sites are along shorelines, using rocks or tree roots for protection.  The den might be 12 feet long, with multiple exits for safety, and a nest lined with fur, feathers or grasses.

While a mink might nibble on a sweet berry, they are active carnivores and require lots of energy to support their active life style and to keep their small bodies warm all winter – no hibernation for these creatures.  Fish, crustaceans and amphibians make up a large percentage of their diet, but they are opportunistic feeders, taking rodents, birds, insects, worms, snakes and muskrats. Nesting waterfowl are at risk from mink, with both the hen and her eggs being sought as high energy food.  Mink are prone to take their catch back to their den or a safe nook for eating, with excess food stored for a later meal.  While suffering through a fish-less day on the Kennebec River a few years ago, I spotted a small mink scrambling along the shoreline rocks.  After a few short dips into the river, the mink emerged with a fat brook trout and scampered off, leaving me with a bruised ego.

The mink may live up to ten years in captivity but their average life span in the wild is probably no more than four years.  Life is tough for the mink with a constant scramble to find food and numerous predators willing to take its life.  Snakes can enter their burrows in search of the young kits.  Owls and other large raptors are capable of taking a mink, along with fox, river otters and coyotes.

The Otter Brook area provides excellent habitat for the mink and her preferred food species.  With a sheltered stream bed, marshy areas and lots of vegetation, plus the adjacent shorelines of Ewing Narrows and Harpswell Cove, this future HHLT preserve will undoubtedly host these beautiful little creatures for many centuries to come.

February 2016