Health and Sexual Signals of Male Asian Elephants (Elephas maximus) in Nagarahole National Park, Southern India

Abstract

Male Asian elephants (Elephas maxim us) were studied at Nagarahole National Park, southern India from November 1998 to May 1999. Information was collected on at least 30 identified individuals for investigation of the possible use of musth and tusk length by males as signals of health and genetic fitness to female elephants. This study followed an earlier study by Watve and Sukumar (1997) which showed a significant negative correlation between tusk lengths and parasite loads in male elephants of the Mudumalai Wildlife Sanctuary, southern India. In this project, musth was studied in . addition to tusk length as a possible indicator of good health. It was hypothesised that musth and tusk length in male elephants would be related to better health and body condition and hence could potentially be considered as signals of better genetic quality, within the framework of Zahavi's theory of honest signaling (1975, 1977) and Hamilton and Zuk's theory of heritable true fitness (1982), respectively. The indicators of better health and body condition used were a subjectively scored body condition index (SCI) and a quantitative assessment of intestinal helminth parasite density (parasite load). Individuals were identified by a combination of several physical features, photographic records were obtained for height and tusk length measurement and information was collected on body condition, parasite loads, musth intensity and social interactions. The following interesting results were obtained: 1. Individuals exhibiting signs of early musth had significantly better body conditions and lower parasite loads than individuals exhibiting no signs of musth. 2. Longer tusks were not significantly correlated with better body condition, lower parasite loads or musth in this study.3. Dominance behaviours recorded in dyadic interactions among male elephants indicated that dominance was associated with musth, height of the animal and tusk length in a high percentage of interactions (100%, 89% and 78%, respectively).The significant association between early musth and better body condition as well as between early musth and reduced parasite loads indicates that male elephants may require better health in order to attain musth. Hence musth appears to be a potential honest signal of better than average health, in males which are able to attain this condition. This information may be used by female elephants in choosing mates. Social interactions among males corroborated this speculation by showing that musth and height in male elephants may be important determinants of dominance, which in tum may influence female choice and reproductive success. Limited samples of male-female interactions suggested that females discriminate between different males, and that male-male dominance interactions may influence female choice. However, small sample sizes limited the extent to which these findings could be extrapolated in this and other elephant populations.