Intrasexual chemical communication and social responses of captive female African elephants, Loxodonta africana

In matrilineal societies, competition between females can occur within and between social units. Dominance hierarchies reduce costly conflicts when reliable cues of status are available, and reproductive condition may alter individual or group status. Female African elephants live in matriarchal groups with linear dominance hierarchies occurring within and between groups; elephants use chemical signals to mediate social interactions. If reproductive condition has important implications for inter- or intragroup behaviour, then females should discriminate between chemical signal sources that reveal reproductive condition. We examined whether trunk-tip contacts between females within a social group were related to phase of oestrus. Observations were conducted on 21 reproductively viable females at nine zoological facilities in North America. Females in the follicular phase received contacts to the urogenital region at a higher rate than did luteal phase females, and contacts increased with approaching ovulation. This supports the existence of an oestrous signal. We also examined whether an oestrous signal was evident by female investigation of urine collected from the luteal and follicular phases of unfamiliar conspecifics. Elephants responded to unfamiliar urine more than to the control, but response rates to the urine types did not differ. Females within a social unit detected differences in oestrus, but they did not show such discrimination to urinary signals from unfamiliar females. Further evaluation of the existence of a female-to-female oestrous pheromone requires assessing responses to urine from familiar individuals. Understanding the relationship between oestrous condition and dominance status can shed light on the adaptive value of sociality.