Thursday, March 20, 2008

Playing Possum?

Sometimes when opossums are cornered, they will simply keel over into a dead faint. Many predators, such as dogs, don't quite to know what to do with a dead opossum, and will walk away. If the predator does leave, the opossum will eventually raise up its head, look around, and if danger has passed, scurry off to cover.

Research indicates that "playing possum" is not really an act. Instead, the possum suffers a kind of nervous collapse. Since opossums aren't well equipped for fighting, their "delicate nervous system" has adaptated by creating an "over ride" mechanism that pushes them into a kind of temporary catatonia which, ironically enough, can help keep the possum alive.

The reason "playing possum" works is that the attack response in many dogs and other predator is also genetic -- it has nothing to do with being "angry" or being "hungry". The reason a fox will kill as many chickens as it can is that the jerky and fluttering movement of the chicken triggers a "mass murder" response within the fox. If chickens simply "played dead," like a possum often will, a vixen would pluck off one hen and be on her way.

Ironically, another animal that will occassionaly go into catatonic shock when cornered is the red fox. A fox bolted into a net will sometimes slip into a kind of momentary catatonia as it's nervous system shuts down, the body stiffens, and a kind of nervous shock sets in. Again, this is a kind of defense mechanism. It must work well enough, for it is employed by two very different animals that are very successful. The red fox is the most widely distributed carnivore in the world, and the possum is one of the oldest animals on the planet.
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4 comments:

YesBiscuit! said...

Years ago I worked in a vet clinic where someone brought in a possum that had been hit by a car and killed. We took the opportunity to open the mouth and look at all the sharp teeth - real horrorshow. That memory has helped maintain my sense of respect for possums all these years.

Anonymous said...

I wonder if this technique would work on my manager?

icr said...

A few weeks ago a 3-foot long lizard lay perfectly still (this was about 5AM) just on the other side of the fence. My Siberian Husky went crazy and dug like a maniac to get at the lizard.

After a few triumphant(forgive the anthropomorphizing-that's the way it seemed) head shakes she dropped the dead lizard to the ground. I threw the lizard over the fence and tranquility returned.

Just needed to kill something I guess.

retrieverman said...

When foxes and dogs go into predatory motor patterns, their brains release endorphins. It's that way with virtually every predator. Those motor patterns are separate from the dissect and consume motor pattern. They have to learn to eat what they kill.

That's why dogs surplus kill.

Most predators will surplus kill if given the opportunity.

There is another theory that surplus killing is of an evolutionary advantage. If a predator can kill more than it needs to eat right then, it can cache what it doesn't eat.

However, I think the latter requires planning on the level that I don't think that species other than humans have demonstrated.

The reason why surplus killing hasn't been seen as often in wild wolves (although it exists) is that it's much harder for wolves to kill wild game species, even in packs. They are successful only between 15 and 26% of the time:

http://www.npwrc.usgs.gov/resource/mammals/severity/index.htm

If wolves have to expend that much energy just to kill one elk, then they aren't going to be in any condition to do surplus killing. But occasionally they do get a into a situation in which they can surplus kill.