02/24/2012 10:31 am ET Updated Feb 24, 2012

Elephant Rampages Blamed On Old Bulls, Bad Role Models For Juveniles

Elephants may give birth to live young, but they can still be bad eggs. A new study shows how seemingly good elephants turn rotten, at least from a human viewpoint, by stealing into farms and wolfing down crops. In Kenya, young males seem to be learning their problem behavior from older bulls, an insight that may influence how conservationists manage clashes between humans and the large animals.

It's a frequent occurrence along the farms surrounding Amboseli National Park, just north of Mount Kilimanjaro in Kenya: Locals wake up to find that their carefully sown tomatoes and onions have been pulled up and their fields mangled—with a few tracks and some scat identifying elephants as the perpetrators. Scientists know that such "crop raiding" is almost exclusively a male endeavor. But why these elephants do it isn't clear.

Most elephants, in fact, never go on raids, says study co-author Patrick Chiyo, a behavioral ecologist at the University of Notre Dame in South Bend, Indiana. He and his colleagues previously estimated that only about 35% of the adult males living in Amboseli regularly gorged on cultivated fruits and vegetables. To get to the bottom of this behavior, Chiyo turned detective.

When an elephant went on an eating binge near the grassy preserve, farmers would contact Chiyo. He'd show up, then follow the tracks back to where the bulls were recouping after their raid. Because all of the roughly 1400 elephants living in the preserve are known by unique marks—such as notches in their ears or missing tusks—Chiyo could tell who was who.

Raiding isn't a young elephant's game, Chiyo's team discovered. Some 20- and 30-year-old elephants did sneak over fences, but bulls over 45 were twice as likely to do so, he and colleagues report online this month in PLoS ONE. Chiyo says this may have to do with musth, prolonged periods of heightened testosterone and aggression levels, which in most male elephants begins when they reach their full reproductive potential around 45 or 50. Males entering musth don't just go looking for mates; they rampage. This hyperactivity may sap the bulls' energy, forcing them to turn to potentially dangerous options, such as crossing into farms, to find food.

But that wouldn't explain why some younger males were also raiding crops. With a little digging, the group found that they were following role models. Youngsters that ran mostly in packs with older bulls were also more likely to raid; in other words, they were learning their habits from patriarchs. That wouldn't be unprecedented in the elephant world. Older female elephants, for instance, often instruct young cows on where to find watering holes.

Wildlife managers might try to break this cycle, Chiyo says. He recommends that conservationists focus much of their energy on chasing away older bulls that wander too close to farmland. Elephants soured on the raiding process might be less likely to teach their tricks to younger animals. "If these older males learn that cultivated crops are always protected," he says, "they may influence their younger associates not to raid as well."

Simon Hedges, a conservation biologist at the Wildlife Conservation Society in New York City, says he's happy to see researchers nailing that older elephants, likely driven by musth, are mostly responsible for crop raiding. Many researchers had long suspected as much but couldn't prove it definitively.

The study "is pioneering in delving into the behavior of crop raiders," adds Lisa Naughton, a geographer at the University of Wisconsin, Madison, who focuses on interactions between human societies and animals. But, she adds, "tweaking behavior" might not be enough to manage problem elephants. Instead, conservationists should strive to limit the temptation of agriculture. That could include fencing off farms or encouraging locals to grow cash crops that aren't as delicious for elephants as a tomato dinner, such as chilies.

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