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Thursday, April 19, 2001

NATURAL SELECTIONS

Intelligent elephant mamas never forget


Elephants form some of the most intimate social relationships seen outside primates. The female-led society provides a high level of care to its members: Little elephants are bathed and carried over obstacles, and mothers frequently touch their young with their trunks. If disturbed, calves and the matriarch leader are protected at the center of the herd.

There are stories of "mourning" behavior among elephants when a family member dies. Elephants have been seen trying to coax dead young back to their feet, burying dead calves under branches and even carrying the bones of dead family members.

Hazel Thompson, a forest warden in Cameroon, once told me the story of a baby forest elephant who had been captured by villagers and kept in a cage of wooden stakes in the village. At night the baby's family group stormed the village and bust the baby out of its prison. The story made the Cameroon papers.

The sudden death of a matriarch can send a herd into what looks like panic, which shows just how important she is. But why is she important?

Scientists based in the U.K. and Kenya think they've answered that question. They found that matriarchs are repositories of social knowledge, and their skill in identifying friends and foes boosts the breeding success of the whole group.

Kenyan elephants are the savanna subspecies of the African elephant, Loxodonta africana (the other subspecies is the forest elephant). Families with matriarchs aged 55 years or over were more likely to show defensive behavior when scientists played the recorded calls of unknown families than when they were played the calls of known neighboring families. Families led by younger females responded far less often to calls from strangers.

Moreover, the results of the seven-year study, reported in today's issue of Science, show that the older the matriarch, the higher the reproductive success of her group.

The lead author of the paper, Karen McComb of the School of Biological Sciences, University of Sussex and the Amboseli Elephant Research Project, Nairobi, said: "We believe this to be the first statistical link between social knowledge and reproductive success in any species. The results indicate the disproportionate effect the hunting and poaching of mature elephants may have for elephant populations."

Larger, older animals are more likely to be targeted by poachers. The research shows that the loss of the matriarch through poaching or hunting would have disruptive ripple effects through the whole family group for years to come. Elephants are an endangered species.

Female elephants become sexually mature at around 14 years, males a little later, but they both continue to grow throughout their lives. The leader's crown often passes to the oldest daughter of the matriarch when she dies. When they become sexually mature, young males are driven out of the group by the dominant male. They start mating at around 25, but are not strong enough to monopolize a group until they are about 35.

The evolution of social intelligence is a hot topic among evolutionary biologists. Dolphins, nonhuman primates and elephants are the top candidates for a form of social intelligence that involves complex communication and behavior, but even parrots and crows are thought by some scientists to qualify. The topic also interests computer scientists working on artificial intelligence. If we can figure out how animals become socially aware, goes the reasoning, maybe we can reproduce it in machines.

Despite all this, says McComb, "we still know little about how wild animals gain and store information about social companions or whether the possession of superior social knowledge enhances fitness."

McComb and her coworkers recorded the calls of elephants and played them back through a custom-built hi-fi system in the back of a Land Rover. Elephants bunch together when danger threatens, so the researchers measured how the diameter of the group changed when different calls were played. They also noted whether the matriarch used her trunk to smell, as experienced leaders use smell to gather extra information on callers' identity.

They confirmed that their results were due to the age of the matriarch, and not to some other factor such as the number of other females or calves in the group. In the Amboseli study population, a single family encounters on average 25 other families during a year, representing around 175 adult females.

Family groups may merge after the spring rains to migrate and feed on the lush new grass. Unfriendly females from other groups may start harassing the calves or start disputes, so it is important the matriarch determines friends from enemies and signals the information to her family. She'll build up this information throughout her long life. Senior elephant matriarchs, at least, never forget.

E-mail Rowan Hooper at rowan@japantimes.co.jp


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