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Can Moose Learn to Fear Predators?

In wildlife parks around the world, recent carnivore reintroduction programs have left scientists and wildlife officials wondering: what happens to animals who have never known predators?

A recent report in the journal Science suggests that formerly "predator-naive" moose can learn to be wary of reintroduced wolves and grizzly bears—quickly.

Disguised as a moose, biologist Joel Berger and his research partner can get close enough to toss urine-scented snowballs at thier subjects and play wolf howls to test the moose's reaction to the scent of predators.

Photo by Joel Berger

Pleistocene Extinctions

The report likens the naivete of moose in predator-free zones to conditions that existed at the end of the Pleistocene era, approximately 10,000-50,000 years ago.

As human hunters spread around the globe in those years, they unleashed a blitzkrieg on prey species that had never learned to fear them. The result of this, plus a possible change in the climate, was the extinction of more than half of the world's large animal species.

The circumstances surrounding the post-Pleistocene extinctions are similar to the present conditions in carnivore-free zones in many areas in the "lower 48" United States and western Europe, where wolves and bears have been hunted to extinction, or forcibly removed to protect other species.

"One consequence of predator extinction is that the prey may lose knowledge of its predators," says Joel Berger, a biologist and one of the authors of the report.

However, the "fact that at least one prey species [the moose] quickly learns to be wary of restored carnivores should negate fears about localized prey extinction," write the scientists.

Learning to Fear

Berger and his colleagues studied the responses of moose to predator sounds and scents in areas where predators were present, predator-free zones, and areas where predators had recently been reintroduced after several decades of absence.

Naive moose—who had not been exposed to predators in decades—were less sensitive to traditional predator cues. In some cases, when presented with the scent of wolf or bear, they casually approached the scent, and did not depart the area.

In comparison, moose in Alaska accustomed to living among wolves were 250 times more likely to bristle at the sound of a wolf howl, say the scientists. Even the call of a raven, a scavenger whose presence often signals a fresh carcass and possibly a nearby predator, was likely to make the moose more alert.

Where predators had been recently reintroduced, such as Yellowstone National Park, the moose seemed to be showing signs of learning fear.

"The moose are still non-responsive to odors—relative to those in Alaska," says Berger. "However, they are learning to respond to howls."

"The response is somewhat puzzling because wolves don't howl when they are hunting. Fearing the wolves' howl appears to be just the first tier of learning," he says.

Some females who had lost their young to predators seemed to develop a "hypersensitivity" to howls. The magnitude of their reactions exceeded those of predator-experienced moose in Alaska, says Berger.

Scientists in a Moose Suit

Berger uses an unorthodox method to get up close and personal with his subjects.

He dons a moose suit, created by a costume designer who worked on Star Wars. With the help of a research partner who makes up the "rear," the two imitate the lumbering gate of their subjects, which allows them to move within observation distance.

To test a moose's response to predators, Berger lobs snowballs soaked with wolf, bear and human urine at the moose. He also plays recordings of wolf howls.

While he can't speak for other species, Berger says that the moose observations are encouraging. Their ability to learn to fear introduced predators suggests a survival instinct that may not have been present in post-Pleistocene animals that became extinct.

"Moose are smarter than we think they are," he says.

Berger hopes to study the response of other prey species in environments where carnivores have recently been reintroduced.

"We'd like to see how bison, caribou, and elk respond to reintroduced predators," he says.

A caribou costume doesn't seem to be in Berger's future, however. "We've found a relationship between body size and ability to tolerate approaches," says Berger.

"The caribou are just too small," he adds sadly.


More Information
Related Websites

Return of the Wolf Read an interview with biologist Douglas Smith of the National Park Service about the recent wolf reintroduction program in the park.

Geoguide: Wolves Explore the natural and human forces that affect the wolf's survival.

Destinations: Yellowstone National Park Find information about visisting the world's first national park.

Fantastic Journeys: Yellowstone In this national Geographic Kids feature explore Yellowstone's fantastic natural phenomena and make the famous geyser, Old Faithful, blow its top!