Friend or Foe? Old Elephants Know.
The quality of this grandmotherly know-how correlates with the number of calves in elephant groups, Karen McComb of the University of Sussex in Brighton, England, and her colleagues report in the April 18 SCIENCE. Herds with especially wise elders enjoy the brightest future, the team found.
"Our findings imply that the removal of older, more experienced individuals, which are often targets for hunters because of their large size, could have serious consequences for endangered populations of advanced social mammals," the researchers warn.
To learn the social connections among elephants, the researchers drew on 28 years' of data from the Amboseli Elephant Research Project, which is directed by study coauthor Cynthia Moss. The records track family patterns and encounters among some 1,700 elephants in Kenya's Amboseli National Park.
Each female African elephant roams with her mother, sisters, and other female relatives. The oldest female leads. In Kenya, such a group typically encounters 25 other families, or about 175 other elephants, each year.
Strangers might spark disputes or harass calves, so unfamiliar calls send a herd into a defensive huddle and inspire much trunk waving, presumably for sniffing the air, explains McComb. In contrast, a herd of familiar neighbors doesn't pose much of a risk.
Elephants can sort their friends from strangers by identifying so-called contact calls. (To hear the calls, check www.sciencenews.org/2010421/fob1.asp) The calls include both sounds audible to humans and lower-frequency rumbles that carry great distances. According to earlier research, a female typically recognizes about 100 peers by their calls.
McComb and her colleagues approached 21 families and trumpeted recordings of contact calls from a loudspeaker mounted on a four-wheel-drive vehicle. The researchers used responses to playback calls from elephants of various degrees of familiarity to predict responsiveness for a family. Matriarchs aged 55 and older proved highly sensitive to the difference between calls from a familiar elephant and those from a stranger.
Bands with these older leaders rarely huddled in response to calls from elephants familiar to the leader. However, these bands were "several thousand times more likely to bunch in response to calls from [complete strangers] than to those with whom they [were most familiar]," McComb and her colleagues conclude from the analysis. In contrast, younger matriarchs' bands were only 1.4 times as likely to huddle for acquaintances than for strangers.
In another analysis, the age of the matriarch turned out to be the best indicator of the reproductive success of the herd as a whole, the researchers report. Earlier work had suggested that the matriarchs know their environment better than younger leaders do and can lead their respective groups to better resources. The social smarts of older elephants may also help boost their herds' success, McComb suggests.
"This study resonates with a study we conducted using elephant warning-call playbacks as a potential deterrent for crop-raiding elephants," says Caitlin O'Connell-Rodwell of Stanford University. That project also showed that herds responded differently to calls from buddies than from strangers.
She now hopes that the "solid result" of McComb's team will convince range managers to prevent the hunting of older female elephants.
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|Article Type:||Brief Article|
|Date:||Apr 21, 2001|
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