Elephant Elders Know Better

August 21, 2008

A WCS study suggests that the experience of matriarchs may help herds survive in the age of climate change, when animals may have to contend with increasing drought

Experience breeds wisdom, especially for elephants. On the East African savannah, where wildlife must contend with regular famine and drought, elephant matriarchs rely on their long-term memories of distant sources of food and water to help their groups get through the worst of times.

According to a recent study by the Wildlife Conservation Society (WCS) and the Zoological Society of London (ZSL) published in The Royal Society’s Biology Letters, old female elephants seem to give their family groups an edge in the struggle for survival.

“Understanding how elephants and other animal populations react to droughts will be a central component of wildlife management and conservation,” said WCS researcher Dr. Charles Foley, lead author of the study. “Our findings seem to support the hypothesis that older females with knowledge of distant resources become crucial to the survival of herds during periods of extreme climatic events.”

Researcher Dr Nathalie Pettorelli of ZSL, a co-author of the study, added that climate change will likely lead to increased drought in Africa. “These grand dames of the elephant kingdom might become increasingly important,” she said.

The researchers examined patterns of calf mortality in Tanzania’s Tarangire National Park during the drought of 1993, the region’s most severe drought in the past 35 years. During a nine-month period, 16 out of 81 elephant calves in the three groups studied died, a mortality rate of 20 percent. The mortality rate of calves during non-drought years is a mere 2 percent.

Researchers found that calf survival correlated with their groups’ movements, and in particular, with the ages of the female members within those groups. Two of the groups left the park to find food and water, and were able to keep their young alive. These two groups had matriarchs that were 45 and 38 years of age. The group that remained in the northern portion of the park throughout the drought suffered 63 percent of the mortality for the year. This group had a matriarch only 33 years of age.

The researchers pointed out that the groups that left the park may have benefited from the specific experiences of their oldest matriarchs, which perhaps were able to draw upon memories of surviving an earlier drought. Some of the oldest matriarchs in these groups were five years or older during the drought of 1958–61. The group that remained in Tarangire in 1993 had no individuals old enough to remember the event.

“It’s enticing to think that these old females and their memories of previous periods of trauma and survival would have meant all the difference,” said Foley.

During the 1970s and ’80s, many of eastern Africa’s largest elephants fell victim to waves of poachers eager to exploit the black market for ivory. They targeted older females with large tusks.

“Hopefully, this study underlines the importance of how crucial older matriarchs are to the health of elephant populations,” added Foley. “Protecting the leaders of elephant herds will be even more important in what may be an increase in droughts due to climate change.”

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