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Extension Forestry & Natural Resources

Wildlife & Fisheries Biology  -  Environmental & Natural Resources  -  Forest Resources



Semi-Aquatic Furbearer Biology and Management

Greg Yarrow, Professor of Wildlife Ecology, Extension Wildlife Specialist

Fact Sheet 27: Revised May 2009

Some furbearers, like raccoons and mink, are classified as semi-aquatic furbearers because they are usually found in association with water.

MINK

American MinkMink (Mustela vison) are semi-aquatic furbearers of the Mustelidae or weasel family. They are one of the most popular weasel-like animals and historically one of North America’s most important furbearing animals. Although no longer as much in fashion, mink is still one of the major wild furs produced in North America.

Mink Characteristics

Mink have an elongated body with the tail comprising 1/3 to 1/2 of the total length. Males measure 22 to 28 inches in length and weigh 2 to 3½ pounds. Females are about 10 percent smaller. Both sexes have a luxurious, dark chestnut-brown pelt for which they are widely sought. The fur is relatively short. The coat consists of a soft, dense underfur concealed by glossy, lustrous guard hairs. Mink usually have white spots and patches on their chin, chest, and belly. The tip of the tail is usually black.

Mink are found in every state except Arizona. In Canada, mink are found everywhere south of the tree line with the exception of a few islands. From the eastern streams to the large reservoirs and the banks of the Mississippi River, mink can be found throughout where appropriate habitat exists. South Carolina mink populations are highest in the coastal marshes and in the upper Piedmont. Sparser populations are scattered over the rest of the state.

Habitat Needs

Mink are mainly associated with wetland or aquatic habitats; however, they may move considerable distances from wetlands in search of food. They are shoreline dwellers, and their basic habitat requirements are a permanent source of pollution-free water and shoreline areas free of grazing or development. The shoreline areas should have adequate vegetation (brushy or grassy areas) to conceal their movements. The availability of den sites (muskrat and beaver lodges or bank burrows, holes, crevices, or log jams) appears to limit mink populations. Mink prefer productive waters with high fish, frog, and aquatic invertebrate populations. The water may be turbid or nutrient-rich; however, the wetland habitat must be pollution-free. Mercury, polychlorinated biphenyls (PCBs), and pesticides such as DDT, DDE, and dieldrin are known to accumulate in the mink’s body tissue and may cause complete reproductive failure. There is strong evidence that in areas with high levels of these pollutants wild mink populations have been adversely affected.

Mink are strictly carnivorous animals, and because of their semi-aquatic habits, they are adapted for preying on both aquatic and terrestrial prey. Feeding studies have indicated that mink are opportunistic predators and eat mice and rats, frogs, fish, crayfish, rabbits, insects, muskrats, amphibians, reptiles, and birds or bird eggs. Availability of any particular food item determines its frequency in the diet. This varies by season and geographical location. In search of food, mink can dive around 20 feet deep, and can swim a depth of 100 feet.

Mink are active mainly at night, although they may be seen during the day. Mink are generally solitary animals, except during the breeding season or when females have kits. Mink home range size is variable and depends on habitat quality, especially the abundance of the food supply and the number of denning sites. Male mink are great travelers, and their home range may include 1 to 4 miles of shoreline (an average of 1½ miles of stream). Females move in a small area during the breeding season, and their home ranges may vary from 1/4 to 2 miles of shoreline (average of 1¼ miles of stream).

Reproduction

Mink are polygamous, and males may roam extreme distances in search of receptive females. Males may fight ferociously with other males during the breeding season, which extends from late January through March in South Carolina. The female remains in heat throughout the entire breeding season with a peak in receptiveness every 7 to 10 days. This allows the female to be mated several times during the breeding season. Mating triggers ovulation, which usually occurs 33 to 72 hours after mating. It is possible for females to have eggs fertilized by 2 or more males if the remating occurs so that there are 6 or more days between ovulations.

Like other members of the weasel family, mink exhibit delayed implantation. The embryos do not implant in the uterine wall or complete their development until about 28 to 30 days before birth. The total gestation period for mink averages 51 days but varies from 40 to 75 days. In late April and May, 1 to 8 blind, naked, helpless young are born (the average litter size is 4). Young mink weigh about 1/3 of an ounce at birth and exhibit tremendous growth. By 7 weeks of age, they will have obtained 40 percent of their adult weight and 60 percent of their adult length. Their teeth appear at 2 to 3 weeks of age, and their eyes open during the third week. The mother raises the young by herself until late summer or early fall when the young leave.

Mink die from a variety of causes, but most mortality is limited to man and pollutants from man’s activities. The effects of trapping on wild mink populations is largely unknown.

RaccoonRACCOON

Raccoons (Procyon lotor) are one of the most adaptable, widespread, and successful wildlife species in North America. They are also one of the most economically and recreationally important furbearers in this country. This crafty animal also provides many hours of enjoyment for raccoon hunters.

Raccoon Characteristics

Raccoons are a very common and easily recognized furbearer. No other mammal in South Carolina resembles this black-masked, ringed-tailed animal. Raccoons have stocky bodies measuring 2 to 3 feet with a broad head and pointed snout. Coloration is generally black above with black-and-white-tipped guard hairs and a pale underfur. Pelts may be variable shades of browns and yellows, with an occasional cinnamon or albino reported. Nearly as rare as the albino is the solid black raccoon, sometimes referred to as a fisher raccoon.

Raccoon HandRaccoons have 5 long, slender toes on each foot that make readily identifiable tracks resembling miniature human hand prints. Male raccoons are larger than females and weigh between 15 and 18 pounds. Females weigh between 12 and 16 pounds. In the northern part of its range, they can weigh as much as 33 pounds. The heaviest raccoon ever recorded was a 61-pound male taken in Wisconsin.

The raccoon can be found in every part of the U.S. except parts of the Rocky Mountains. Raccoons can also be found in Mexico and southern Canada. Over the past 40 years this adaptable animal has been expanding its range northwards into Canada. It is estimated that the North American raccoon population is 15 to 20 times larger today than it was before a population explosion in Raccoon Printsthe 1930s and 1940s helped the raccoon expand its range. Although the raccoon is native to North America, it has been introduced into the Soviet Union and Germany.

The raccoon can be found in every South Carolina county. Population densities are highest along the coast and decline steadily inland. Raccoons are most abundant in counties with large amounts of wetlands, bottomland hardwood swamps, and grain fields.

Habitat Needs

This adaptable animal can occupy a wide variety of habitats, although it prefers mature hardwood forest areas with numerous den trees close to water. Since raccoons are water-associated animals, water is a very important habitat requirement. Raccoons depend on wetland and aquatic habitats for a large portion of their food. They are seldom found far from water.

Raccoons select a variety of different types of dens to give birth and raise young. The most common den is in a tree. Tree dens may be found in any hollow limb or tree trunk that is large enough for a female raccoon and her litter to fit into. Ground dens are important for raccoons, especially in areas that are lacking tree dens. Abandoned fox or groundhog burrows are most often used as ground dens. Other types of dens include rock crevices, caves, drains, abandoned buildings, barns, and brushpiles. Dens of all types are located near water.

The lack of suitable den sites may be a factor limiting raccoons in regions of the state. Management practices such as leaving den trees and placing raccoon nest boxes could increase populations in these areas. Also the protection of raccoon habitat, especially wetland habitat, is needed to ensure stable populations.

Raccoons also need brush thickets, ground dens, hollow logs, or trees for cover to escape predators and for daytime resting sites. During the day, raccoons may rest on bare tree limbs or gray squirrel nests.

Feeding areas vary according to the time of year and the types of available food. Since raccoons are omnivorous, their feeding habitats will be as varied as the type of food they pursue. Raccoons use aquatic habitat such as streams, rivers, and ponds when feeding on crayfish, fish, and amphibians. They use overgrown fields, corn, and other grain fields mainly in the fall and summer when berries, grains, and insects are the mainstay of their diets. Hardwood forests provide important hard and soft mast, such as persimmons, acorns, and wild grapes. Raccoons usually stay long periods in these small feeding areas.

Food

Raccoons are opportunistic animals and have been known to feed on a variety of food items, which vary seasonally and with different locations. Some known foods include carrion (dead animals), garbage, birds, mammals, insects, crayfish, mussels, a wide variety of grains, and many different types of fruits. Only in the spring do raccoons eat more animal than plant food. During the spring their diet consists of crayfish, insects, and small vertebrates. Fruits and berries, along with corn, are most prominent in their diet during late summer. In autumn, fruits, corn, and crayfish are important food sources. Acorns become the most important food during the winter months and early spring.

Space Needs

Raccoons are mostly active from sunset to sunrise and tend to den up during daylight hours. Peak feeding activity is generally over before midnight. Raccoons are least active during the winter months. During periods of low temperatures and snow cover, raccoons will typically sleep for several months in their dens. When temperatures climb above freezing for several days during late winter, raccoons may leave their dens to feed.

During the breeding season, adult males may be territorial. During this time home ranges of these males usually do not overlap one another. Females are not territorial, and their home ranges may overlap. Several female home ranges may be located within one male home range. Raccoons may have home ranges up to two miles long although most are about one mile long. Home ranges vary considerably depending on habitat conditions and population densities. Raccoons will move long distances when food is scarce or populations are low. Raccoon densities vary from one raccoon per acre to one raccoon per 100 acres.

Reproduction

Breeding season for raccoons in South Carolina ranges mostly from January to February, with peak activity occurring in February. Although males may mate with several females each spring, there is some evidence of pair bonding between males and females. Female raccoons may form a bond with a familiar male about one month before mating. The female will also mate with other males at the peak of estrus. Any type of bond terminates after breeding season, leaving the female to care for the young.

Sixty-three to 65 days after mating, 2 to 8 deaf, blind, and helpless kittens (an average of 3 per litter) are born between March and June. The young weigh less than 1/2 pound. Their eyes and ear canals open when they are 18 to 24 days old, and permanent teeth are in place by their third month. Infant raccoons feed on the mother’s milk until they leave the den at around 10 weeks of age. The mother may move the kittens to ground dens when they can walk. The mother and kittens travel together until the young leave in the fall or winter. In northern areas, young raccoons may delay dispersal until spring.

Female raccoons may become sexually mature and breed at less than one year of age. Breeding by kittens depends on food availability as this affects body condition.

Raccoons die from a variety of causes. Canine distemper and rabies are the only two diseases likely to affect their numbers significantly. Starvation can be a major mortality factor for young raccoons during the winter months. Human-induced mortality is thought to be the primary cause of death in raccoons.

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