The experiments showed that honeyguides in the Kidero Hills, Tanzania are over three times more likely to cooperate with people giving the local Hadza whistle, than people giving the ‘foreign’ Yao trill and grunt. And the honeyguides in the Niassa Special Reserve, Mozambique are almost twice as likely to cooperate in response to the local Yao trill and grunt, than the ‘foreign’ Hadza whistle.
The phenomenon seems to be self-reinforcing: honeyguides learn to recognise that a specific call indicates a good honey-hunting partner, and humans are more successful in attracting the birds if they use this call.
People who use a different call are less likely to attract a bird to guide them to the honey – so it’s in their interests to stick to the sounds used locally.
“Once these local cultural traditions are established, it pays for everyone – birds and humans – to conform to them, even if the sounds themselves are arbitrary,” said joint lead author Dr Brian Wood, an anthropologist at the University of California, Los Angeles.
The researchers compare this to different human languages, in which the sounds of words are arbitrary, but everyone has agreed on their meaning.
Spottiswoode added: “Just as humans across the world communicate using a range of different local languages, people across Africa communicate with honeyguide birds using a range of different local sounds.”
Like language, these culturally determined calls convey an underlying meaning – signalling a desire to partner with the bird to find honey.