Porcu-power: chemical warfare

Defense-minded mammal deploys odor to ward off foes

Posted: Sunday, February 18, 2007

Porcupines have more in common with bees and skunks than most people realize.

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A bee sting, a stinky blast from an angry skunk, or a swat from a porcupine are memorable experiences.

These animals all prefer to avoid confrontation, and they all use their weapons for self-defense. Their ideal world is one where would-be predators have a single bad, unforgettable experience and learn never to harass them again.

That's why they have built-in warning systems. The bright yellow and black coloration of bees and wasps makes it easy to remember what they look like. The same is true of the skunk's distinct black and white markings. The image becomes associated with the consequence.

Animals that are poisonous to eat also use conspicuous colors. The vivid poison dart frogs of Central and South America are a good example. So are Southeast Alaska's own poisonous rough skin newts.

A predator that eats one of these toxic meals may survive after getting violently ill. The visual image of those conspicuous colors becomes connected with the bad dining experience. Next time the animal sees those visual cues, it's reminded that the newt isn't meal material.

The porcupine has a similar strategy, but it uses an olfactory signal, not a visual sign. Its distinctive smell reminds predators not to mess with it. Porcupines broadcast their pungent warning when they are alarmed and their quills are bristled erect.

The odor is generated by a patch of skin on the porcupine's lower back called the rosette. Volatile compounds are secreted by the skin in the rosette. These compounds coat specialized quills growing out of the rosette, which help broadcast the smell.

Biologist Uldis Roze, a professor at Queens University in New York, identified a compound called delta-decalactone as the key element of the warning smell. He did his chemistry, but he used his nose as well.

He described it as similar to the smell of a goat or an exotic cheese.

Roze is a porcupine expert who has written books and papers on the big rodents. He suggests the warning odor, in connection with an initial quill strike, produces what's called a conditioned aversion in predators.

For an animal that's had a bad experience with a porcupine, the smell, like warning coloration, is a reminder that this animal is trouble.

Humans aren't generally aware of the odor, but we don't have a particularly gifted sense of smell compared to most other mammals.

And unlike the dog, coyote or wolf that tries to jump a porcupine, we don't stick our faces right up against the porcupine's back and tail.

• Riley Woodford is the editor of Alaska Wildlife News and producer of the "Sounds Wild" radio program. He writes for the Division of Wildlife Conservation at the Alaska Department of Fish and Game. He can be reached at riley_woodford@fishgame.state.ak.us.

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