Behavior

Nearly all species in the family are nocturnal, although occasionally diurnal sightings of mouse opossums and water opossums have been reported, and some species of Monodelphis are reportedly primarily diurnal. Many scansorial species take to the trees when threatened, whereas terrestrial species run with a characteristic gait. No species is particularly fast during escape behavior. One species, the Virginia opossum, feigns death when threatened by a predator, lying on its side, gaping its mouth spasmodically, and emitting a strong musky smell. Other defense behaviors found in the family include gaping and snapping at intruders while hissing loudly and secreting musk from

A southern opossum (Didelphis marsupials) wards off a dog. (Photo by Joe McDonald. Bruce Coleman, Inc. Reproduced by permission.)
A red mouse opossum (Marmosa rubra) shows aggressive behavior. (Photo by Art Wolfe/Photo Researchers, Inc. Reproduced by permission.)

the anal region. The water opossum dives under the surface and then propels itself with strong strokes from the hind legs.

All opossums are primarily solitary, avoiding contact with each other. After dispersal, juveniles do not keep contact. Males and females come in contact only during the female es-trus for a short period of time. Individuals generally remain in a home range, but this is almost never defended. Instead, when two animals coincide in space and time, they avoid each other. At least in the bare-tailed woolly opossum, Caluromys philander, social dominance is clearly established on the basis of age and body mass. Older, heavier males dominate younger, lighter ones, and agonistic behavior is exacerbated by the presence of females. Interspecific aggression may occur only as a result of the generalized opportunistic behavior to procure food; one Didelphis reportedly attacked, killed, and partially consumed a Philander opossum after an encounter.

Opossums are silent animals the vast majority of the time; sounds are produced only when they are threatened and these are only hisses and explosive gasps. Foraging behavior is exploratory and continuous. Opossums use primarily their sense of smell to locate food. Stalking is seldom used to capture animal prey, but sight and hearing are continually used in the search for food. Young opossums, particularly mouse opossums, emit a loud chirping cry when detached from the female's nipple. This induces the female to approach and grasp the young, and push it under the venter, where it reattaches itself to the nipple.

Predators of opossums include a variety of snakes, foxes, owls, ocelot (Leopardis pardalis), puma (Puma cencolor), and jaguar (Panthera onca). Indigenous human groups in the Neotropical region often include the larger species of opossums in their diet. Didelphis albiventris has been shown to have an antibothropic biochemical factor in its blood and milk that neutralizes the venom of poisonous snakes.

Longevity records in the wild rarely reach two years, with many species barely surpassing one year. In captivity, longevity is extended with reports of three to five years for species such as Marmosa robinsoni, Caluromys philander, and Chironectes minimus. The record is seven years for a captive Caluromysiops irrupta.

A murine mouse opossum (Marmosa murina) eats fruit after dark on a branch 15 ft (4.6 m) above ground in the lowland Amazon rainforest of northeast Peru. (Photo by Gregory G. Dimijian/Photo Researchers, Inc. Reproduced by permission.)
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