(Featured Image: Young mink on Seedskadee National Wildlife Refuge by Tom Koerner, USFWS)
Minks and river otters are semi-aquatic mammals that live throughout our diverse Virginia, including our Eastern Shore natural areas. They are not uncommon animals, however they are not easily observed. These two members of the weasel family have streamlined long bodies and they move quickly and efficiently in the water. If you are lucky enough to see their whole body, you might be able to tell a river otter right away by its larger size and long tapered tail. River otters are quite a bit longer and bulkier (about 2/3 larger) than minks. Minks are about the size of a ferret.
Northern River Otters range in length from 26 to 42 inches, or 66-107 cm. Their tails make up a third of their length. Males are larger and heavier; about 25 pounds, while females average around 18 pounds.
Minks are known for their beautiful fur. Males are larger than females and measure from 13 to 17 inches, or 33-43 cm. Males weigh 1.5-3 pounds. and females weigh 1.25-2.25 pounds.
A few observation hints:
- If the dark brown, long shaped animal is swimming, try to notice if some of the body is visible. Sometimes a whole mink’s back is visible since it may swim higher in the water.
- Minks have pointier noses and make a “V” shape wake on the surface of the water.
- A swimming river otter is mostly submerged and creates a “U” shape wake with its rounder nose.
- Both animals have whiskers – since the river otter is bigger, then the whiskers may be more noticeable. Their whiskers are useful to locate bottom fish and crustaceans in deeper, darker waters.
Clues along the water’s edge
Belonging to the same family with similar habitats, minks and otters share some behaviors while also having distinct differences as well. For example, both animals have a fondness for sliding on or down muddy or snowy banks. Otter slides tend to be about a foot wide and these paths have been seen gliding across level ground of freshly fallen snow or down wet muddy hill running into streams or rivers. Wildlife biologists and photographers have watched otters use slides repeatedly, sometimes with young or other adults and it is considered playful behavior (sounds like fun to me). Minks also coast on snowy ground, through snow tunnels or downhill leaving a narrow slide mark of about four inches wide. Minks are solitary animals so they enjoy sliding alone. Minks are naturally good at socially distancing in the wild.
Otters will roll around on certain grassy areas and these areas tend to get matted down. These spots are typically used as a scent marker location. Otters regularly deposit their unpleasant scent from their anal glands in these matted down grass spots and create scent piles.
All weasels have the ability to release a strong scent and minks will do so when disturbed but it’s definitely not as strong as its skunk relative.
Tracking down more evidence
Looking for footprints is a great way to find evidence of minks or otters along waterways or connecting pathways. Take a couple photos and look up animal tracks online or in a field guide.
Diet and deposits
Minks and river otters are carnivores and their diets vary upon seasonal protein availability. Minks will eat a variety of small mammals, fish, eggs, birds and frogs. River otters eat fish, frogs, crayfish, snakes, turtles and aquatic invertebrates. Minks tend to kill their prey by biting it in the neck and often dragging it back to its den.
River otters do not have any predators other than humans. Minks have many predators including foxes, bobcats, owls, alligators and humans. They will try to defend themselves with their sharp claws and teeth and strong-smelling musk.
Den dwellers
Female river otters prepare a found den by lining it with soft plant material before offspring arrive. They use an existing natural cavity which could be an old muskrat or beaver home, or a hole in the river bank, hollow logs or stumps. Although nests are almost always near the water, a river otter nest was once discovered in a woodchuck hole quite a distance from the nearest water.
River otters do not create their own dens. Minks are also den dwellers and can create their own dens in stream banks. Minks will change locations, using a variety of places such as under logs, in a tree cavity, along a stream bank, or even old or occupied muskrat homes. Sometimes the mink will kill the inhabitants and move in.
Reference Books:
- Brown, Larry N., 1997, A Guide to the Mammals of the Southeastern United States.
- Murie, Olaus J., 1974, A Field Guide to Animal Tracks.
- Stokes, Donald and Lillian Stokes, 1986. A Guide to Animal Tracking and Behavior.
- Terwilliger, Karen, 1991. Virginia’s Endangered Species.