Prey animals can lose and regain very easily the fear of predators

Jun 21, 2007 09:48 GMT  ·  By

When the cat's away/The Mice will play. Prey animals, like the moose, caribou, bison and elk can lose their fear of predators if they are not constantly hunted by them, as found by Joel Berger of the Wildlife Conservation Society (WCS) in New York. But they were also found to "relearn" their fears very quickly, in just one generation, a good news for programs trying to reintroduce predator species into their natural habitats. This is translated into an initial plummeting of the prey populations when a predator is re-introduced after a long absence, but equilibrium will be restored shortly after.

In his 10-year research, Berger traveled from Greenland (where wolves do exist), the Arctic archipelago of Svalbard (with only polar bears) and Norway (where wolves and brown bears were exterminated) to Yellowstone and Grand Teton National Parks (where wolves have been re-established after periods of absence), but also in Eastern Siberia, Boreal Canada and Alaska, where predators are still found: wolves, brown bears and in Eastern Siberia, tigers, also.

In each location, Berger recorded wolf howling or tiger roaring and tracked the reactions of the prey. Animals living in places where the predators had been exterminated displayed lower levels of vigilance, clustering behavior and flight responses than those living under constant threat of being preyed upon. Siberian elks reacted five times faster to the recordings than those in Colorado's Rocky Mountain National Park, where top predators have been missing for about 90 years.

The prey animals were also exposed to recordings of calls made by howler monkeys, whose vocalizations vary in frequency and therefore sound like howling wolves. The prey animals, even those hunted by wolves, ignored the howlers of howler monkey, resembling wolf vocalizations, showing they could tell the difference between sounds emitted by known threats and other sources.

In a single generation, fear can be restored: bisons in Yellowstone National Park, where gray wolves were reintroduced in 1995 after a nearly 70-year absence, reacted more alertly than those from Boreal Canada, where natural wolf populations still exist. "It's good news [for] northern temperate and arctic fauna that they figure it out pretty fast," Berger told LiveScience.

"Because initially they may get hit hard, but they will learn. When gray wolves were reintroduced into Yellowstone, some people said 'Ten years from now, we will not have elk.' Well, there's still a lot of elk there. The same is true for Wyoming." The lack of top predators affects severely the ecosystems from overgrazing.

"If prey species become afraid, they tend to move around more and not concentrate on vegetation in certain areas. There's a release, the vegetation is given a reprieve, and all the species that rely on vegetation, like migratory birds, do better when these large carnivores are back in the system. But allowing predator species to repatriate their natural environments is not enough. They must also be allowed to breed, so their populations grow large enough that their presence is felt once again." said Berger.

This is one program concerning crucial problems: at a time when over $23 million have been spent to re-introduce wolves in the northern Rocky Mountains, the animals' federal protection is going to expire and the states of Wyoming and Idaho have already come with proposals that would decrease by as much as 85 % of these once-protected wolves.

"There's a density effect. If you have just a few wolves that are put into a system, they're still far below what the number should be when the system is balanced. They're unlikely to create this effect where the species are moving about." said Berger.