Chimpanzees make an extra effort to warn neighbours that seem ignorant of danger.
Catherine Crockford and Roman Wittig at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and Klaus Zuberbühler at the Budongo Conservation Field Station in Masindi, Uganda, tested whether chimpanzees (Pan troglodytes) adjust their alarm calls according to whether their listeners seem aware of a nearby hazard.
Wild chimps heard recordings consisting of either an alarm call — indicating that the unseen caller had noticed danger — or a rest call, implying ignorance. After they heard the recordings, they were presented with a hazard in the form of a model snake. Chimps that saw the snake after hearing rest calls issued more warnings than chimps exposed to alarm calls, suggesting that they were taking their compatriots’ perceptions into account when deciding how strongly to raise the alarm.
These cognitive abilities in apes might have laid the foundation for the evolution of language, the authors say.