Monday, November 23, 2009

Why do chipmunks change their mind when they cross the road?

Here's an experience we all have on the highway:

"I was driving with a friend of mine once when a chipmunk ran out into our lane. He must have thought he didn't have enough time to get across so he turned around and ran in the other direction. Then he changed his mind again and ran back towards the median. He continued this running back and fourth until we hit him." Source

Squirrels and rabbits do the same thing. But the reason they "zigzag" has nothing to do with changing their minds. It's a predator defense--and your car is the predator!

The main predators of these small animals and rodents are:
  • In the air--eagles, hawks, and owls.
  • On the ground--coyotes, foxes, weasles, etc.
Both kind of predators, and especially the birds, are limited in how fast they can turn. The prey, being smaller, can turn faster. So the predator tries to compute the prey's course, and aim for where it expects the squirrel to be a second later. By constantly changing directon, the squirrel confounds the hawk. It worked wonderfully for squirrels for millions of years, until autos came along.

So the squirrel isn't changing its mind. It's just an automatic reaction--an instinct.

"Hold on!," you say.  "If it's a predator defense, it didn't work too well with my car."  True, but your car wasn't acting like a predator, trying to pursue the chipmunk.  If anything, you were trying to avoid it.  In this case, the zigzagging works in reverse.  As you turn away from the chipmunk, it randomly turns your way.  Squish!

Wait, it gets better

If zigzag is a good defense, even better is... pretending to zigzag! That's right, some animals have flags that make it look as if they are turning. The cottontail rabbit in the US has a white tail, like a flag, that it waves this way and that as it runs. To the predator in hot pursuit, the white tail is the most obvious thing in sight. When suddently it seems to turn, the predator is confused for a split-second. This may be enough to allow the rabbit to escape.

The white-tailed deer uses the same defense. The tail shows the brown backside when it's down, contributing to the deer's overall camouflage. But when alarmed, the tail comes up in an instant, and wags randomly from side to side as the deer runs off. A deer can run very fast, and any pursuing wolf or cougar is going to have to leap onto it--but how can they compute the trajectory, with that tail is creating confusion?

Some species of small birds seem to use a similar defense. You can see them bobbing this way and that as they feed on a branch. When a predator approaches, a bird is going to take flight--the approaching hawk will have to aim for somewhere besides where the bird is at the moment. But where? So the bobbing creates uncertainty. Perhaps the best example is the spotted sandpiper. It feeds in the open, where it's very vulnerable, and it constantly bobs in a very amusing manner.

...And still better

So, if turning is your defense, then being able to turn "on a dime" is better. Rabbits take this kind of defense to its logical conclusion. Rabbits have eyes positioned on the tops of their heads, so they can see almost in all directions at once. Their ears are large and sensitive, and swivel in all directions.

And, they can leap and start to run in any direction. Picture how the rabbit is built. Its large hind legs are positioned under its center of gravity, not in the rear, as in a dog. So while the rabbit sits muncing on some greens, it is prepared to dart in any direction. If you've chased a rabbit, you know that they usually wait till the last second, before they dart off. They force you to show your hand, then react unpredictably.

This is all a long winded-way of saying that roadkill is the classic example of... unintended consequence. Neither we nor the animals want it to happen.  Technology out of control.  It's time to give more thought to how animals can get across our highways safely.   

Inventors needed.... rodent radar?  Wildlife experts are working on the problem.  There are underpasses for grizzlies and salamders.  There are warning sysgtems to alert drivers when deer are near the highway.  But the percent of highways protected is miniscule.  Just a token, really.

Find out more
Thinking anew about a migratory barrier: roads (with great photo)
As Cars Hit More Animals on Roads, Toll Rises

In Banff National Park in Canada, "the growing number of cars and other vehicles in the park is claiming the lives of an increasing number of elk, bears and other animals.  Road building and other development has artificially divided the herds of animals, raising the problem of inbreeding."  Source

"Citing estimates that put the cost of cars slamming into deer on American roadways at $1.4 billion a year, including property damage and bodily injury — not to mention the 200 human deaths each year from such crashes — officials and researchers from a number of states are pooling their resources to find ways to keep deer off the highway."  Source

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