Chimpanzees moving through the forest take into account other chimps' ignorance or knowledge of a threat when they decide to raise the alarm.
Apes were more likely to make warning calls when they spotted a venomous snake if others in their troop had not seen the danger, researchers found. As chimps in the know arrived on the scene, they passed the warning on to others who lagged behind but were still within earshot.
Video footage of wild chimps foraging in Uganda's Budongo forest show apes at the front of their groups jumping with surprise on spotting a model snake lying camouflaged in the undergrowth. When the chimps regain their composure, they call out with repeated “hoos” to alert those behind them that a threat lies ahead. They were seen to make calls less often when other chimps already knew of the danger.
The behaviour suggests the animals knew what their companions knew and made decisions on what warnings to give based on that information.
Catherine Crockford, who studies ape communication at the University of St Andrews, said: “Lots of animals give alarm calls and are more likely to do so if there's an audience, but these chimps are more likely to call if the audience doesn't know about the danger. It's as if they're picking up on differences in ignorance and knowledge in others. The chimps would sometimes jump when they saw the snake, but they didn't call then. They would only call after going back for a second look. So there's a dissociation between their emotional reaction and the vocalisation. The call is not a knee-jerk reaction to the snake, it's intelligent behaviour.” Ms. Crockford worked with researchers at the Max Planck Institute for Evolutionary Anthropology, in Leipzig and the Budongo Conservation Field Station, in Uganda, to investigate 33 wild chimps.
When confronted with danger, chimps scream or bark if the threat is serious, such as an ambush by a leopard. But they respond to less serious threats with gentle hoos. Ms. Crockford said the study suggests humans are not alone in knowing the minds of others, an ability possibly pivotal in the evolution of language as it allowed humans to share information and boost collective knowledge. “More of the essential ingredients needed to kickstart complex communication are evident in chimpanzees.” — © Guardian Newspapers Limited, 2011
