CREATURE FEATURE: Mink

A nocturnal member of the weasel family, the mink (Neovision vison) rarely seen but is common throughout Illinois despite a decline in numbers over the past century due to the loss and degradation of aquatic habitats.

Checking nest boxes designed for squirrels, but heavily utilized by screech owls on the family farm, my father and I discovered, first-hand, another trait of the mink. Standing at the top of a 20-foot ladder, with my hand poised over the entry hole to prohibit any occupant from escaping, I felt a thump against my gloved hand. Looking down at my record-keeping partner I said “something wants out.” Staring intently at the entry, I moved my hand, and simultaneously we yelled “mink climb trees!” Inside we found a fox squirrel, a nearly surgically precise incision on its belly allowing the mink to turn its prey inside out.

For the most part, mink spend most of their time within 100 feet of the water’s edge. A long, streamlined body shape not only minimizes drag while swimming, but maximizes this carnivore’s ability to enter stream-side burrows hunting for prey. Mink may dig their own burrows, or recycle those dug by muskrats and skunks, constructing numerous entryways and lining the burrow with vegetation.

Recently, the Illinois Natural History Survey conducted a project to study stream-dwelling mink in the agricultural region of east-central Illinois. Funded by the Illinois Department of Natural Resources’ Furbearer Fund, the study focused on developing a broader understanding of the mink, including its movements, home range sizes, survival rates, diets and parasites. Key findings include:

• Radiolocations of mink confirmed the importance of riparian (stream or ditch) habitats for mink.
• The home range of males was substantially larger than females (about 4.2 km, or 2.6 miles, of stream length compared to 1.4 km, or 0.9 miles).
• The survival rates for males was lower than females, especially during the February through April mating season when males are most mobile. Most (75 percent) of the mortality of radio-tagged mink was away from a stream and attributed to vehicles (7), coyotes (6), poison (3) and one from an undetermined disease.
• Contrary to many studies on the diet of mink, the primary food source of central Illinois mink was not muskrats but crayfish (summer), with the addition of mammals in the fall, and fish as the major food source in the winter.
• The majority (77 percent) of captured mink tested positive for Toxoplasma gondii, a protozoal parasite that is a health risk for humans and wildlife.

According to Bob Bluett, recently retired Illinois Department of Natural Resources (IDNR) Wildlife Diversity Coordinator, several recent studies have determined that the Illinois mink population is widespread, common and stable.

“From 2000 to 2004, IDNR monitored the presence of mink near 78 bridges in the state,” Bluett explained. Each spring, tracks or scats were encountered on about 70 percent of those transects. Additionally, surveys in east-central Illinois conducted by researchers at the Illinois Natural History Survey produced similar results, and researchers at Southern Illinois University at Carbondale encountered sign at 88 to 100 percent of locations in the southern third of the state, with no trend over time.

Like all wildlife species, maintaining a healthy mink population that allows for harvest requires quality habitats, which includes protecting and restoring wetland habitats, restricting livestock access to riparian habitats, improving water quality (reduction of soil particles and chemicals) and creating grass waterways.

Mink trapping is legal statewide from November 10 through February15. (NOTE: the 2017 regulation change eliminated the previous two season structure). Consult the annual Illinois Digest of Hunting and Trapping for season dates and regulations.

In the 2015-2016 Illinois Trapper Report: Harvest, Effort, and Motivations conducted by the Illinois Natural History Survey under U. S. Fish and Wildlife Service Federal Aid Project Number W-112-R-25, mink were among the species least often targeted by trappers, although according to Bluett, annual harvest of both mink and muskrat varies heavily based on the current pelt value.

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Kathy Andrews Wright is retired from the Illinois Department of Natural Resources where she was editor of Outdoor Illinois magazine. She is currently the editor of Outdoor Illinois Wildlife Journal and Illinois Audubon magazine.