African elephant vocal communication I: antiphonal calling behaviour among affiliated females

Abstract

African elephants, Loxodonta africana , are well known for their use of a low-frequency ‘rumble’ vocalization, which is thought to function in long-distance communication. Less work, however, has been conducted on short-distance communication within groups, and on spontaneously occurring vocal exchanges among identified individuals in particular. This is due in part to the fact that low-frequency rumbles are difficult to assign to individual callers. We collected vocal data on a group of six female African elephants housed at Disney's Animal Kingdom to determine whether they exchange rumbles in alternating sequences (also known as antiphonal calling). Subjects wore collars outfitted with microphones and radiotransmitters that allowed identification of individual callers, and behavioural and endocrine data were collected so that vocal activity could be examined in the context of social behaviour and reproductive state. First, we found that females did not produce rumbles at random, but were nearly twice as likely to produce rumbles shortly after rumbles from other group members. Second, the relative dominance rank and reproductive state of callers did not affect the probability of vocal response, but affiliative relationship with the caller had a strong influence on rumble response. Females were most likely to respond in kind to the rumbles of their most affiliated partners compared to less affiliated group members. Third, video analysis showed that rumble exchanges occurred in variable contexts, including when animals were out of contact, during reunions, and while in close proximity. Also, affiliated partners often vocalized in sequence when approached by dominant individuals. The results of these analyses show that affiliated female African elephants exchange rumbles antiphonally, and imply multiple functions for such vocal exchanges.