Mustelids, or weasels, include weasels, otters, and mink, among others. At one point, skunks were classified as members of the weasel family, but are now considered their own unique group of mammals. The Forest Preserves of Cook County has been actively tracking and monitoring weasels and other fur bearers for many years now. Weasels are most often tracked using radio-transmitters.
All native weasels are voracious predators and will often hunt down more than their fair share of food, caching away any extra. Weasels are very territorial of each other and will often attack and even kill a member of their own species (or other species of weasel). All weasels smell bad and have glands that release a thick and putrid liquid.
Wildlife biologists have several techniques for figuring out what a wild animal eats. Common techniques employed include analysis of fecal samples, analysis of stomach contents, and analysis of stable isotopes.
Stable isotope analysis is performed in a biological laboratory at a university campus. Whiskers from the animal can be plucked when captured and sent to a laboratory. By analyzing the carbon to nitrogen ratio of each whisker segment, one can determine almost exactly what that animal has eaten during its recent life! For wildlife in Cook County, stable isotope analysis have revealed a much more opportunistic diet than what is often assumed, especially for weasels and other Cook County predators like coyotes.
Mink (Neovision vision)
Minks are aquatic but can often be found (and are very good at) climbing trees. They are relatively large compared with most other weasels and are about 22-26 inches in length with dark brown or black fur with a white blotch on the chest or belly. When one encounters mink in the wild, the white fur from their belly will stand out. Mink are opportunistic predators and will often eat squirrels and muskrats. Mink are often solitary except during the breeding season. Population studies of mink and muskrats have revealed an almost consistent 2-year gap between an increase in the population of minks and an increase in the population of muskrats, suggesting that muskrats are a top prey selection of minks.
Badger (Taxidea taxus)
Badgers have poor eye site but are nonetheless skilled predators. They are active day and night. They often excavate large holes at night eating ground squirrels and woodchucks. They are stocky and muscular with short but powerful legs. They are large in size and are about 27-30 inches in length. The mating routine of badgers is rough and aggressive, and it is not uncommon to find blood and fur scattered about after copulation.
Striped Skunk (Mephitis mephitis)
Skunks are no longer classified as weasels but share many similarities in behavior and physiology. Skunks are active at night and in the Forest Preserves are often found near picnic groves and other open spaces eating grubs and insects. Skunks can be captured for analysis rather easily, since they are slow and awkward runners. As long as a tarp or burlap is covered before they can spray, skunks can easily be neutralized. It is also easy to step out of the way if they start to spray.
Skunks have very sensitive paws that allow them to detect vibrations in the ground, aiding in their search for earthworms and grubs leaving in the soil. Deep blood vessels allow skunks to run through thickets and brambles without serious lacerations.
Skunks and bats are both major vectors of rabies, and in part as a result of radio-telemetry research conducted in Cook County, it is now illegal in Illinois to trap and release nuisance wildlife.
Main population control factors of skunks are disease and severity of winters. Skunks can be vectors of canine, feline, and mustelid diseases! As such, they have served as great vectors for disease research and monitoring.
Long-tailed Weasels (Mustela frenata)
Long-tailed Weasels are large but smaller than mink. They have a distinctive white belly with dark gray or brown fur on top. They have tiny feet, and their foot prints are not much larger than those of mice and other smaller rodents, their preferred prey items. It is not uncommon to encounter their tracks among mice tracks. Long-tailed Weasels are short-lived, around 2-3 years to no more than 5 years. Their close relative, the Least Weasel (M. nivalis) is extremely rare in Cook County, and the well-known Ermine weasel (M. erminea) is found north of Illinois.
River Otter (Lontra canadensis)
River otters were common in Illinois during early European Settlement, but due to unregulated hunting and habitat loss were lost from Illinois by 1930, and until recently have not rebounded. From 1994-1997, 346 otters from Louisiana were released in Illinois. They were also delisted as an endangered species in 2004. The estimated population is now about 30,000 in Illinois, including Cook County! The 2012-13 hunting season was the first in many years to include trapping of otters.
Otters, like many other weasels, are voracious and opportunistic predators. Prey includes fish, frogs, clams, muskrats, turtles, young beavers, and even water beetles! Otters will drive out beavers and muskrats from their lodges and devour their young. Otters quickly decimate their food supply and must eventually move elsewhere, especially if they hunt in smaller, more isolated ponds and wetlands. A common indication of the presence of otters are piles of clam shells left behind, although muskrats do this, too. Otters will also eat catfish and other large fish, even if the fish is larger than themselves! The contents of their latrines are mostly mucous.
River otters are mostly active at night, and they have large ranges, especially in rural areas. They are the largest members of the weasel family in Illinois and can weigh up to 30 pounds! They have tiny ears so that water does not go into them, and they exhibit delayed implementation. Breeding occurs in January-April, and only until the female finds a suitable location or good weather conditions will she gestate. Baby otters, referred to as pups, will gestate in only two weeks! Otters, like most weasels, are often solitary and are intolerant of the pretense of other otters, although sometimes males will stay close to the female, especially if the female is in heat. During the winter, otters can take refuge in abandoned beaver and muskrat lodges, can can swim below the ice in search of food.
Otter track patterns are easily distinguished by their skid-bound pattern:
|Figure 1: Diagram showing skid-bound pattern of river otter tracks.|