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Monday, November 22, 2004 - Page updated at 12:00 A.M.
Squirrel behavior is not so nutty
By Steve Grant
Those little gray piles of fur, flesh and blood are as numerous on roads this time of year as pumpkins on doorsteps.
These would be your squirrel roadkills.
Every motorist is familiar with the sad scenario: A squirrel dashes out into the road, stops, zigs, then zags and zigs again, right under one of the wheels.
Your street, you say, is a furlong of fur.
Given that most drivers are not aiming for squirrels, and given that squirrels often could avoid eternal rest by running across the road without stopping, the question is: Are they as stupid as they seem?
Stephen Hawking they are not, but scientists are discovering that squirrels are far craftier than we've given them credit for. Squirrels know which acorns are most perishable and eat those first, and they are capable of what may be consciously deceptive behavior to protect food they have cached.
Michael Steele, a professor of biology at Wilkes University in Wilkes-Barre, Pa., says his research indicates "they are, on a daily basis, making very careful behavioral decisions that are critical for winter survival."
Sylvia Halkin, a professor of biology at Central Connecticut State University, is studying deceptive behavior in squirrels, following up on a student's observation that squirrels sometimes buried an acorn then moved nearby and pretended to bury another acorn, behavior that might confuse another animal attempting to find the cache.
She and some of her students conducted an experiment in which they gave squirrels peanuts and then watched them bury them. Then the students dug up the peanuts.
Subsequently, they found that when they gave the squirrels peanuts, the squirrels would bury a nut, then pretend to bury other nuts nearby. Or the squirrels would dig many holes before burying a single nut in one of them. Or they might try to bury the nut under a bush where the researchers could not see it. Or the squirrel would climb a tree and put the nut in a nest.
What surprised the students was that they were expecting only one kind of deceptive behavior, but the squirrels demonstrated a whole bag of tricks to confuse creatures, human or otherwise, who might steal their stash.
"Deceptive behavior has been documented in a number of species of animals," Halkin said. But overall "it is rare. It gives us a glimpse into the kinds of mental processes that may be going on in their heads."
Steele and Peter Smallwood of the University of Richmond determined that squirrels selectively bury those acorns that are least perishable, such as those from red oaks, ensuring a food supply during winter, while immediately consuming acorn species that are most perishable, such as those from white oaks.
When they do bury a white oak acorn, they first bite out the embryo, which prevents the acorn from sprouting. Experiments indicate that by doing so, the white oak acorn will remain edible for six months, Steele found. If they did not do that, the acorn would put out a taproot and become inedible.
A recent experiment, not yet published in the scientific literature, involved young squirrels raised in captivity who had never seen acorns before. The squirrels showed a strong tendency to remove the embryo from white oak acorns (they did not always do so cleanly), suggesting there is an innate tendency toward that behavior.
The reason squirrels are plentiful in many places this year is that acorn crops have been good in recent years, said Peter Good, a wildlife biologist with the Connecticut Department of Environmental Protection.
Unfortunately, the best documentation of the bountiful squirrel population is the growing number of them run over by cars. Several factors are at work in the roadkill boom. This is what biologists often call the "fall shuffle," when young squirrels especially are moving around in search of food, often crossing roads to find acorns or other food, Steele said.
Compounding the situation, squirrels are particularly active just after dawn and just before dusk, which coincides this time of year with morning and evening rush hours, a convergence that is bad news for squirrels.
That zigzag behavior, of course, is a defensive response to throw off predators.
But a car is another matter.
"They move at a speed not encountered by many things in nature," said Halkin.
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