(I did a quick search but did not find this question. Please forgive me if it’s been asked before…I think it’s pretty obvious, but who knows?)
There is nothing I enjoy more on warm, summer nights than to take Poochie on a nice stroll through the neighborhood. However, I’d guess that we average about two skunk sightings during each outing. We haven’t been sprayed yet but I think we’ve come pretty close. (I thought Poochie was sniffing a trunk at one point; I didn’t see the skunk behind it, about two inches from Poochie’s snout!)
Each skunk sighting is more or less the same…I’ll catch a quick flash of white out of the corner of my eye, confirm it is indeed a skunk by the tell-tale waddling, and then Poochie and I will steer clear.
Here’s my question: why aren’t skunks just black in color? Why in the world would Mother Nature allow a big white stripe (which might as well be a neon sign) to evolve on the back of a nocturnal rodent? If I’m so quick to pick out the creature, then surely its predators are even better, yes? Does the stripe have some evolutionary benefit? And wouldn’t an entirely black skunk be more fit for survival?
Mind, Poochie and I are not complaining. But we are damn curious.
The stripe is a warning to stay away or you’re going to get sprayed.
It’s not like Pepe Le Pew, by the way, the spray doesn’t come out of the tip of their tail but out of a gland near their anus. Right before they spray their tail sticks straight up and the hair on the tail sticks straight out like a Christmas tree.
Notice what you did–you saw it was a skunk, and you steered clear. And this is the reaction of most predators when they see a skunk. So the white stripe protected the skunk better than camouflage would have.
[nitpick]Skunks aren’t rodents. They were once thought to be mustelids (like ferrets, otters, and badgers) but zoologists now place them in their own family, Mephitidae. Both mustelids and skunks are in the order Carnivora, along with cats, dogs, bears, and seals. Rodents are in the order Rodentia.[/nitpick]
It’s warning coloration, like the black-and-yellow coloration of wasps, the orange-and-black of monarch butterflies, or the red-yellow-and-black of coral snakes. Animals that look harmless but which actually have highly potent defenses benefit by being easy to recognize.
Since skunks are active at night, when colors are less apparent, and since most of their potential predators are mammals, which generally have poor color vision, they rely on high-contrast black-and-white coloration as a warning, rather than the bright coloration used by diurnal animals that are preyed on mainly by birds, which have good color vision.
Also skunks are carnivores (Order Carnivora), not rodents.
[OT] I’ve never seen a skunk run away from anything. I’ve stopped at a safe distance and thrown rocks at them to chase them off the trail and a few have raised their tail at me. Even when approached buy a curious dog, it never seems to enter a skunks mind to run away. [/OT]
They could of course be neutral colored, and spray everything that gets near. The drawback is that it takes time and energy to make more spray, and so they would rather scare predators away rather than confront them, hence the easy fix.
Yeah the stripe serves as a warning unless you were my dog. I had me a dog when I was little and he got skunked, not once, not twice, but THREE times in one summer.
You think he’d have learned. But no…Did you know a dog can actually spit?
I had to clean Mr Dog and that’s no pleasant task, that skunk odor gets everywhere, from between the toes to in this gums.
You can read some good info about the adaptive strategy in this wikipedia article under the “Warning and signalling (semantic colours)” and the “Mimicry or pseudo-sematic colours” sections.
I’ve always been rather interested in the species that have carved a niche out for themselves by posing as the species that actually have the arsenal that the coloring/morphology/smell/taste is usually associated with, and such mimicry is testimony that the warning system is a very successful evolutionary strategy.
It’s been speculated that the Giant Panda’s black-and-white coloration may also be for warning purposes. Although it’s a slow-moving herbivore, it has powerful jaws and teeth and can give a serious bite. The pattern may warn tigers and bears that it’s more dangerous than it looks.
To expand on what’s already been said, the deterrent effect of a skunk’s chemical defense requires less energy output and is easier on the skunk if predators learn and remember it – and associate it with skunks in the future. So being instantly recognizable actually helps make the deterrent more effective. Skunks don’t want to be jumped on and possibly wounded; they want predators to see them coming and stay the heck away.
How does a predator know that a skunk can spray? How common is it for a random predator to have previously been sprayed, or even seen a skunk in action?
Well, even if we create a Mephitidae to hold skunks, the Mephitidae would be a sister taxon of the Mustelidae. In other words, whether skunks are a subfamily of mustelids, or whether mephitids and mustelids are sister families of a larger superfamily is a matter of taste.
From being young and stupid. Generally young mammal predators start getting bolder and bolder as they age but are still mostly attached to their mother. Skunks won’t really run in most cases and are easily cornered by young and curious predators who are still learning to hunt. They don’t stay curious for long and they don’t forget what that white stripe means.
Oddly, domesticate dogs can’t learn this it seems. At least in my horrible experiences.