WASHINGTON -- When wolves and grizzly bears returned to parts of the Yellowstone basin of Wyoming, they feasted on the innocence of moose that had not seen such predators and didn't know to run.
It took only a few bloody encounters, however, for the moose to learn to fear the marauding meat-eaters, according to a study appearing Friday in the journal Science.
Joel Berger, first author of the study, said when the wolf was reintroduced into the Yellowstone areas and the bears started migrating into areas where they had long been absent, they could easily catch, kill and eat moose that had not seen such predators for 10 to 15 generations.
Initially, said Berger, the study's first author, the wolf and bear could easily approach a moose because the animal made little attempt to run.
"We were like forensic scientists" in studying the kills, said Berger, a professor at the University of Nevada, Reno, and researcher for the Wildlife Conservation Society. He said it was clear from tracks and other evidence that the moose were easy prey.
"We got direct evidence of grizzlies killing 10 adult moose," said Berger. An adult moose can weigh almost 1,000 pounds.
Other evidence was found of younger moose standing almost still as they were approached and killed by the wolves that ate them.
That quickly changed. Within a season after the killing began, moose became alert and wary, startling at wolf howls and moving quickly on when they sensed danger.
Berger and his colleagues tested the predator alertness of the Yellowstone moose and compared it with that of moose in Alaska, where wolf and bear have been historic predators.
Before the Yellowstone moose had developed their wariness, Berger said, the animals would pause for only 30 seconds when researchers played recorded wolf calls, then nonchalantly return to their feeding.
After the predator attacks began, however, recorded wolf calls caused the moose to become alert and restless. Often they left a feeding site and retreated from the sounds. Moose mothers who had lost calves to wolves, for instance, became five times more alert, as measured by the time spent looking for danger, than unmolested moose mothers. The reaction of the mothers that had lost calves was very much like that of Alaskan moose who have never known the absence of predators.
"Wyoming moose that have lost even one of their offspring to predators may become as savvy as their Alaskan cousins within a single generation," said Berger.
The finding is reassuring for many conservationists who had worried that the return of predators could lead to the extinction of whole herds of prey.
Such an eradication, called the "blitzkrieg theory," is what some researchers believe happened when humans first arrived in North America some 50,000 years ago. About half of the American animal species weighing more than 100 pounds -- including the camel, horse, mammoth and some types of sloth -- became extinct after the arrival of man.
It could be, said Berger, that the eradicated animals were simply not smart enough ever to learn that humans were dangerous.
"Our data are consistent with the idea that some prey species may not recognize certain kinds of predators," said Berger. "This is total speculation, but it may be that the animals that went extinct in the Americas when humans appeared were those that were not as smart as the moose."
Berger said that bears also have been reintroduced in parts of Scandinavia, and researchers there also found that the moose, after a bloody season, quickly learned to avoid the new predators.
Researchers now are studying the reaction of elk, caribou and deer in areas where predators have been introduced in recent years. Berger said the elk is now the major menu item for wolves in the Yellowstone basin, but it, like the moose, seems to be learning either to avoid or to fight the wolf.
John L. Gittleman, a professor of biology at the University of Virginia, said Berger's study "is an important work" that lays to rest some worries that prey animals would be wiped out by reintroduced predators. Understanding this risk is important, he said, because predators are being reintroduced in at least 173 locations worldwide.
On the Net: Science magazine: http://www.eurekalert.org
Wildlife Conservation Society report of study: http://wcs.org/home/wild/northamerica/725
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