Opossum

ORDER: Marsupialia
FAMILY: Didelphidae
GENUS: Didelphis
SPECIES: virginiana

Opossum


I. DESCRIPTION:
Males are larger than females. HBL is 13-20 inches. They weigh from 5-12 lb. The pelage consists of underfur and white-tipped guard hairs and coloration is gray, black, reddish, or sometimes white. Face is white and head markings of three dark streaks are sometimes present-one running through each eye and another running along the midline of the crown. The basal tenth of the tail is furred and the remainder is almost naked. All four feet have five digits with claws except the first toe of the hind foot is clawless, thumb-like and opposable for grasping. The female has a well-developed pouch which commonly holds 13 nipples arranged in an open circle with one in the middle.

II. GEOGRAPHICAL RANGE AND HABITAT:
Occurs naturally from New Hampshire to Colorado, and from southern Ontario to Costa Rica. There are introduced populations on the west coast from British Columbia to San Diego, and in parts of Arizona, western Colorado, and Idaho. Usually favors moist woodlands or thick brush near streams or swamps, but adapts to many other environments, including urban.

III. DIET:
Omnivorous. Varied diet includes small vertebrates, invertebrates, carrion and many kinds of vegetable matter. They especially like young birds, eggs, mice, frogs, fish and insects.

IV. LIFE CYCLE/SOCIAL STRUCTURE:
Largely nocturnal, spending the day in hollow tree trunks, under piles of brush, in abandoned burrows, even in attics or garages. They construct rough nests of leaves and grasses, carrying material with their prehensile tails. The opossum is nomadic and stays in a particular area for six months to a year before moving on; there is no territoriality, but individuals will defend the space occupied at a given time. Basically solitary and antisocial except between the sexes during breeding season. Vocal repertoire consists of a hiss, a growl, and a screech, which are used in antagonistic and defensive situations, and a metallic lip clicking heard during a variety of situations.

Females are polyestrous with first matings in winter or early spring, depending on the latitude. After just one mating, females are no longer receptive and will attack persistent males. Since opportunities to mate are scarce, males fight fiercely over fertile females. Two litters per year are usual with an average of 110 days between litters. Gestation period is 12-13 days. Young are remarkably undeveloped except for their claws and are less than 1/4 inch in length. Twenty would fit in a teaspoon and it would take 217 of them to make one ounce in weight. There are usually about 20 young, but with only 13 nipples some perish right away. Additional mortality occurs later and average pouch young varY from 6 to 8. Young release their grip on the nipple at 60 days, leave the pouch temporarily at 70 days, and are completely weaned and independent when they are 3-4 months old. Sexual maturity is attained at 6-8 months and females have 2 reproductive years. Very few opossums survive their third year of life, though some in captivity have lived up to 7 years.

V. SPECIAL ADAPTATIONS:
Strong swimmers. Can climb well, with the help of the prehensile tail. In the northern part of its range, it accumulates fat in the fall and remains inactive for several days at a time, but does not hibernate. Resistant to venomous snake bites (from those that normally share their habitat) and immune to most contagious and viral diseases. Has 50 teeth and will open mouth wide to frighten an attacker.

Death feigning, referred to as "playing possum" is a passive defensive tactic employed in the face of danger. The opossum becomes immobile, lies with the body and tail curled, opens the mouth, and is apparently insensitive to stimuli. This condition can last less than a minute or as long as six hours. Although it seems partly under the conscious control of the animal, there are physiological changes suggesting a state aimilar to fainting in humans. Possible advantages of this reaction are that predators lose the visual cue of motion or are deterred by the defacation accompanying the catatonia. It may have evolved to prevent aggression within the species.

VI. INTERPRETIVE INFORMATION:
Marsupials are thought to have originated in North American more than 100 million years ago, then spread to other regions of the world. Today they are largely confined to Australia and South America. Opossums are the only marsupial that range north of Mexico. Captain John Smith of Virginia's Jamestown Colony first recorded the Algonquin Indian word "opossum" meaning "white beast" in 1612. One of the few animals that has prospered with the advent of man, it has extended its range north and west with settlers as land was cleared for agriculture.

VII. STATUS IN WILD:
Hunted for food, sport, pelts, and as a predator of poultry but unlike many marsupials, the opossum is flourishing. Because it is extremely adaptable and able to eat a wide variety of foods, it can live very well in the urban areas. Although it is attacked by a large number of predators, especially man, it breeds rapidly and individuals that are killed are soon replaced.

VIII. BIBLIOGRAPHY:
1. Austad, Steven. "' Possums are Survivors", National Wildlife. Dec/Jan, 1985.
2. Nowak, Ronald. 1991. Walker's Mammals of the World. Johns Hopkins University Press, Baltimore, MD. Vol. 1, pp.19-20.
3. Opossums Society of the United States, P.O. Box 16724, Irvine, CA 92713. Written handouts. 1993.
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