On Easter Monday I dropped in to see my parents and dragged the Northerner with me (he wasn’t kicking and screaming, I should add). My mother who is an ace cook and has the love-handles to prove it, made us a wonderful meal: masala chicken; daal; rice and parathas. Unlike me, the Northerner likes to focus his attention on every morsel and rarely utters a word, unless it’s for second helpings. Must be a chef-thing. I on the other hand am happy to continue rabbiting while still being able to appreciate the delicate flavours and textures of every mouthful. And my best mate, Mamma Afrika (MA), likes to make ‘umming’ sounds of delight while eating (almost like a hum, but not). It’s so subtle you can only just make it out if you’re within earshot, but it’s her barometer of how good the food is. If there’s silence, then you gotta worry.
In fact MA’s response to food quality is not too dissimilar to how bonobos (also known as pygmy chimpanzees) react. In a study published today Dr Zanna Clay and Professor Klaus Zuberbühler of St Andrew’s University, examined the behaviour of captive bonobos at Twycross Zoo in the East Midlands after they were played the recorded calls of other bonobos who had found different types of fruit and then measured their reaction.
Dr Clay said: “Studies on language-trained bonobos have revealed their remarkable abilities in representational and communication tasks, but there hasn’t been much research on their natural communication. Bonobos produce five different types of sound when they find food: a bark; a peep; a peep/yelp; a yelp and a grunt. We found that individual calls were relatively poor indicators of food quality, but bonobos also mix calls together into longer sequences. The test we carried out was to see whether food quality could be derived from these sequences.”
The authors trained four captive individuals to find two types of fruit, kiwi (preferred) and apples (less preferred) at two different locations, the left and the right hand side of the enclosure. Dr Clay says she also cut the fruit up into tiny pieces so the apes would have to actively forage for it through the long grass (enrichment); she wasn’t going to make it easy for them, this extra effort would also help to stimulate them and “keep them guessing”. This was done for more than a month in the run up to the tests. Then during the test days, just before being let out into the enclosure, the apes were played different recordings of bonobo calls after they had found either kiwis or apples. The authors found how they behaved depended on what they had heard.
Dr Clay said: “We found that subjects put more effort into foraging according to which call sequence they had just been played. It’s the first time that a playback experiment has been done with bonobos. We were hopeful that they would respond but there wasn’t a guarantee. Apes are infamous for being difficult to work with in these sorts of experiments because they are much harder to convince than monkeys. These results provide the first empirical evidence that bonobos are able to extract information from listening to the vocal sequences of other individuals; which is very important if they’re in the forest.”
I love the idea of “barking or yelping” about food quality, but I think if I did that on my next meal out, I would probably be frogmarched to the door rather than being rewarded with a treat.
The paper, Bonobos Extract Meaning from Call Sequences is published in PLoS One now.