Experienced female elephants act as guardians of social knowledge, listening to other elephants' calls and then signalling to their families who is friendly and co-operative and who might present problems by harassing calves or starting disputes. If these senior pachyderms can't immediately recognise friends versus foes, their families may spend too much time being defensive and not enough time reproducing. The results of a seven-year study are reported in the 20 April 2001 issue of Science. The UK and Kenya-based researchers also showed conclusively that the breeding success of elephant families is linked to the age of matriarchs, the females who lead family groups.
This finding has important implications for conservation as older, larger elephants are more likely to be targets for hunters and poachers, and killing these individuals is likely to weaken entire family units for years to come.
Using data on African elephants at the Amboseli Elephant Research Project in Kenya, the researchers showed that families with matriarchs aged 55 years or over were several thousand times more likely to bunch together defensively in response to calls from families they rarely encountered than families with which they often associated. In contrast, families with matriarchs aged 35 years were only 1.4 times more likely to respond to strangers than acquaintances. If senior elephants were simply more confident and relaxed overall, they would have been less responsive to all calls. In fact, the study suggests, their social skills are better and they recognise allies more easily.
The results were gained using high powered hi-fi equipment. Elephant calls were recorded to digital audio tape and then played back through custom-built bass box loudspeakers in the back of a Land Rover. The researchers then noted whether the elephants bunched together-meaning the diameter of the group reduced in terms of elephant body lengths. The researchers also recorded whether the elephants used the tip of their trunk to smell. Like bunching, elephant families with experienced matriarchs showed greater discrimination in smelling to confirm the identity of callers than families with younger leaders.
To be sure the observations were the result of the matriarch's knowledge, the researchers also noted the number of females in the group, the average age of females other than the matriarch, the number of calves, the age of the youngest calf and the presence or absence of adult males. None of these was found to be statistically significantly linked to bunching.
The superior discriminatory abilities of older matriarchs were linked to reproductive success for the family unit, with the age of the matriarch a significant predictor of the number of calves produced by the family per female reproductive year over the course of the study.
Lead Science author Karen McComb said: "We believe this to be the first statistical link between social knowledge and reproductive success in any species. The results highlight the disproportionate effect the hunting and poaching of mature animals might have for elephant populations. Other large mammals, such as whales, dolphins and chimpanzees also live in 'fluid' social systems where an ability to recognise friends amongst many acquaintances might be expected to have an impact on reproductive success."
Female African elephants live in matrilineal family groups led by the oldest female or matriarch. Within the Amboseli study population, a single family unit encounters on average 25 other families during a year, representing a total of around 175 adult females.
The major funding for this work was provided by the Biotechnology and Biological Sciences Research Council (BBSRC). Additional support came from the University of Sussex, the Amboseli Elephant Research Project, the Zoological Society of London, and the Tusk Trust.
Karen McComb's team included researchers from the University of Sussex, the Institute of Zoology at the Zoological Society of London, and the Amboseli Elephant Research Project, Nairobi, Kenya.
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