FLY SWITCHING BY ASIAN ELEPHANTS - TOOL USE TO CONTROL PARASITES

A type of tool use by Asian elephants alluded to over a century ago by Darwin is their use of branches as a switch, allegedly to repel flies. In a study of Asian elephants used to take tourists for rides into a national park in Nepal the elephants were observed to grab branches spontaneously and switch with them during the rides and to switch frequently with branches presented to them at the stable. A study of 15 adult working female elephants was conducted to determine whether the use of swtiches was related to intensity of fly harassment, and if the behaviour functioned to reduce fly intensity around the elephants. Elephants were presented with switches resembling those they spontaneously picked up during rides. At daybreak (0600 hours), when no flies were present, the median switching rate was about 30 per 10 min. At four other observation times during the day (approximately 0800, 1100, 1500 and 1800 hours), when fly counts ranged from a median of 1·5 to 4·0 flies on and around the elephants, the median switching rate ranged from 150 to 186 per 10 min. A comparison of switching rate with daytime temperature changes and feeding schedules indicated that switching is not a manifestation of confinement stereotypy or a behaviour related to cooling the body. In an experiment on eight elephants conducted during the time of day when fly activity was most intense (approximately 1100 hours), fly counts were conducted for 10 min when no branch was available and immediately thereafter for 10 min when the elephants were presented with branches. The median fly count was significantly reduced by 43%. Elephants of the study sometimes modified the branches by removing side stems or shortening the branch. The frequency of fly switching by wild Asian elephants is not currently known. However, among the captive elephants of this study, fly switching would appear to be one of the most frequently employed instances of tool use. © 1993 The Association for the Study of Animal Behaviour.