Long-distance communication of acoustic cues to social identity in African elephants.

Research on long-distance vocal communication in mammals has tended to focus on the maximum distances over which a vocal signal might be physically detectable. For example, because elephants and some whales communicate using infrasonic calls, and low frequencies are particularly resilient to attenuation, it has often been assumed that these species can communicate over very long distances. However, a wide range of acoustic characteristics typically carry information on individual identity in mammalian calls, and frequency components crucial for social recognition could be distorted or lost as distance from the source increases. We used long-distance playback experiments to show that female African elephants, Loxodonta africana, can recognize a contact call as belonging to a family or bond group member over distances of 2.5 km, but that recognition is more usually achieved over distances of 11.5 km. We analysed female contact calls to distinguish source- and filter-related vocal characteristics that have the potential to code individual identity, and rerecorded contact calls 0.53.0 km from the loudspeaker to determine how different frequencies persist with distance. Our analyses suggest that the most important frequency components for long-distance communication of social identity may be well above the infrasonic range. When frequency components around 115 Hz become immersed in background noise, once propagation distances exceed 1 km, abilities for long-distance social recognition become limited. Our results indicate that the possession of an unusually long vocal filter, which appears to incorporate the trunk, may be a more important attribute for long-distance signalling in female African elephants than the ability to produce infrasound.