California Department of Fish and Game "Harvest Species"

Life History

Opossums are active year-round and inhabit moist woodlands and brushy habitats at low elevations. They are common to abundant throughout California west of the Sierra Mountains. The preferred habitats include riparian, moist woodlands, brushy habitats, wetlands, agricultural areas, and residential areas that provide abundant food and cover. Water is required for species success so higher concentrations may be found near water sources, especially during dry years. Dense conifer forests and grasslands do not seem to support large numbers.

Activity occurs throughout the night from dusk to dawn, peaking at midnight. During periods of extreme cold they are far less active and may be active during the day. They may also remain inactive for several days in their burrows during the winter. Fat is accumulated in the fall and used as energy during these cold periods when food may be limited.

Rough nests of leaves and other material is constructed in hollow logs, snags, rocks, piles of brush, or in the burrows of other animals. They have also been documented using man-made structures such as buildings and culverts.

The opossum is a highly opportunistic feeder eating a wide variety of animal and vegetable foods. Carrion and insects are usually the principal food items, but fruits, berries, grains, green vegetation, earthworms, and fungi may also be important. Food may be obtained on the ground or in shrubs or trees. The availability of food in the winter is an important limiting factor.

Home ranges vary in size and are usually oblong or elongated following a watercourse. Night movements are erratic and because they are somewhat nomadic, den sites are changed often. Opossums are not territorial but they are solitary and aggressive.

Mating occurs from January to February and June to July. Gestation is 12.5 to 13 days when a litter of 6 to 25 young may be born. There are two peak periods of litter production, January to March and May to July. Two litters are born every year and should the first be lost, the female will immediately return to estrous and breed again. The female has 13 nipples in a pouch on her underside where the young climb after birth. If more young are born than she can support, some do not survive. The young that do make it to the pouch are extremely altricial and remain attached to a nipple for 50 to 65 days. Weaning of the young occurs at 90 to 105 days. Females reach maturity at 5.5 to 7 months but probably do not breed in their first year. Males usually reach sexual maturity at about 8 months. Females usually have two years of reproductive activity. Although they live three to five years in captivity, their life expectancy in the wild is 1.3 years or less. Populations are usually composed of young of the year.

Natural predators include owls and dogs. Motor traffic and severe winter conditions are also important sources of mortality.