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If threatened, an opossum will either flee or take a stand. To appear threatening, an opossum will first bare its fifty teeth, snap its jaw, hiss, drool, and stand its fur on end to look bigger.[1] If this does not work, the Virginia opossum is noted for feigning death in response to extreme fear.[2] This is the genesis of the term "playing possum", which means pretending to be dead or injured with intent to deceive.[3] The reaction is involuntary and triggered by extreme fear.[2] In this inactive state it lies limp and motionless on its side, mouth and eyes open, tongue hanging out, and feet clenched.[1] Fear can also cause the opossum to release a green fluid from its anus whose putrid odor repels predators.[2][4] Heart rate drops by half, and breathing rate is so slow and shallow it is hardly detectable.[1] Death feigning normally stops when the threat withdraws, and it can last for several hours.[1][4] Besides discouraging animals that eat live prey, playing possum also convinces some large animals that the opossum is no threat to their young.[2] "Playing possum" in response to threats from oncoming traffic often results in death.[5]
Opossums are omnivorous and eat a wide range of plants and animals such as fruits, grains, insects, snails, earthworms, carrion, snakes, birds, mice, and other small animals.[6] Insects such as grasshoppers, crickets, and beetles make up the bulk of animal foods.[7] Small animals include meadow voles, mice, rats, birds, and frogs.[8] Attracted to carrion on the side of the highway, opossums are at an increased risk of being hit by motor vehicles.[4] Plant foods are mainly eaten in late summer, autumn, and early winter.[7] These include raspberries, blackberries, apples, acorns, beechnuts, and vegetables.[7] Opossums in urban areas scavenge from bird feeders, vegetable gardens, compost piles, garbage cans, and food dishes intended for dogs and cats.[7][8] Opossums eat up to 95% of the ticks they encounter.[5][9] Opossums are estimated to eat up to 5,000 ticks per season and help prevent the spread of tick-born illnesses, including Lyme disease and Rocky Mountain spotted fever.[9] The Virginia opossum has been found to be very resistant to snake venom.[10][9] Persimmons are one of the opossum's favorite foods during the autumn.[11] Opossums in captivity are known to engage in cannibalism, though this is probably uncommon in the wild.[12] Because of this, placing an injured opossum in a confined space with its healthy counterparts is inadvisable.
The Virginia opossum is most active during the spring and summer.[7] It does not hibernate but reduces its activity during the winter.[6][13] It may not leave its den for several days if the temperature drops below -7 to -4 degrees C.[7] Both males and females are at greater risk of injury during breeding season.[14] Males extend their range in search of mates which puts them at greater risk of injury from motor vehicles and predators due to unknown territory.[14] Females carrying young are slower moving and have to forage earlier in the evening and later into the night, also increasing their risk of injury from motor vehicles and predation.[14]
The breeding season for the Virginia opossum can begin as early as December and continue through October with most young born between February and June.[14] A female opossum may have one to three litters per year.[14] During the mating season, the male attracts the female by making clicking sounds with his mouth.[14] The female's estrus cycle is 28 days and lasts 36 hours.[14] Gestation lasts 11-13 days and the average litter size is 8-9 infants, although over 20 infants may be born.[14] Opossums have a very high mortality rate of their young; only one in ten offspring survive to reproductive adulthood.[15] Newborns are the size of a honeybee.[7] Once delivered through the median vagina or central birth canal, newborn opossums climb up into the female opossum's pouch and latch onto one of her 13 teats.[14] The young remain latched for two months and in the pouch for 2 1/2 months.[14] The young then climb onto the mother's back where she carries them for the remainder of their time together.[14] It is during this time that the young learn survival skills.[14] They leave their mother after about four or five months.[16] Like all female marsupials, the females reproductive system is bifid, with two lateral vaginae, uteri, and ovaries.[17] The male's penis is also bifid, with two heads, and as is common in New World marsupials, the sperm pair up in the testes and only separate as they come close to the egg.[17]
Compared to other mammals, including most other marsupials except dasyuromorphians, opossums have unusually short lifespans for their size and metabolic rate.[18][19] The Virginia opossum has a maximal lifespan in the wild of only about two years.[20] Even in captivity, opossums live only about four years.[21] The rapid senescence of opossums is thought to reflect the fact that they have few defenses against predators; given that they would have little prospect of living very long regardless, they are not under selective pressure to develop biochemical mechanisms to enable a long lifespan.[22] In support of this hypothesis, one population on Sapelo Island, 5 miles (8 km) off the coast of Georgia, which has been isolated for thousands of years without natural predators, was found by Dr. Steven Austad to have evolved lifespans up to 50% longer than those of mainland populations.[22][23]
Yellowmouth Rockfish | |
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Threatened(COSEWIC 2010). | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Scorpaeniformes |
Family: | Scorpaenidae |
Genus: | Sebastes |
Species: | S. reedi |
Binomial name | |
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