How to speak chimpanzee: Researchers find their 'hoo' sound has multiple meanings

  • A study examining animal alarm calls found that chimpanzee's 'hoo' sound means three different things: alert, travel and rest, depending on variation
  • Need to stay together in low visibility habitat may have caused evolution of calls
  • Call informs receivers how to behave so signaller and receiver can stay together

By MOLLIE CAHILLANE FOR DAILYMAIL.COM

Published: | Updated:

A new study examining animal alarm calls has found that chimpanzees' 'hoo' sound means three different things: alert, travel and rest.

Previous studies suggested that species which needed different escape responses from different predators were more likely to have different alarm calls, but little research had been done on what caused calls to vary in less urgent situations. 

To address this gap in knowledge, the Max Planck Institute for Evolutionary Anthropology examined different sounds chimpanzees make.

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Previous studies suggested that species which needed different escape responses from different predators were more likely to have different alarm calls, but little research had been done on what caused calls to vary in less urgent situations

Previous studies suggested that species which needed different escape responses from different predators were more likely to have different alarm calls, but little research had been done on what caused calls to vary in less urgent situations

'We examine a quiet contact vocalization of chimpanzees, the 'hoo'', said Catherine Crockford.

'We found that chimpanzees have at least three acoustically different 'hoo' variants, each given in a different behavioral context: alert, travel and rest.'

In order to maintain cohesion, chimpanzee receivers need to respond differently to sounds in each context.

When a rest sound goes out, receivers must stay in the vicinity of signallers. But in travel contexts, receivers must approach signallers. 

And in alert contexts, receivers will still approach signalers, but more slowly. 

'Chimpanzees benefit from cooperating with bond partners, and are thus particularly likely to gain from staying close to cooperation partners', said Crockford. 

'However, chimpanzees live in low visibility habitat, such that even when separated by short distances visual signals or non-specific vocal signals are likely to be unreliable in maintaining cohesion. 

Thus, encoding contextual information in quiet 'hoos' may facilitate cohesion - and therefore cooperation.'

The researchers also found there is low emotional arousal associated with their production.

They reseachers also discovered that the acoustic properties of the various sounds couldn't be easily explained by emotional state, unlike for most other non-human animals

They reseachers also discovered that the acoustic properties of the various sounds couldn't be easily explained by emotional state, unlike for most other non-human animals

They also discovered that the acoustic properties of the various sounds couldn't be easily explained by emotional state, unlike for most other non-human animals.  

The need to stay together in low visibility habitat may have facilitated the evolution of different calls, with each call informing receivers how to behave in order for signaller and receiver to stay together. 

'One factor driving the evolution of call diversification may have been the demands of cooperative activities,' said Crockford.

WHICH ARE SMARTER: CHIMPS OR CHILDREN?

Most children surpass the intelligence levels of chimpanzees before they reach four years old.

A study conducted by Australian researchers in June 2017 tested children for foresight, which is said to distinguish humans from animals.

The experiment saw researchers drop a grape through the top of a vertical plastic Y-tube.

They then monitored the reactions of a child and chimpanzee in their efforts to grab the grape at the other end, before it hit the floor.

Because there were two possible ways the grape could exit the pipe, researchers looked at the strategies the children and chimpanzees used to predict where the grape would go.

The apes and the two-year-olds only covered a single hole with their hands when tested.

But by four years of age, the children had developed to a level where they knew how to forecast the outcome.

They covered the holes with both hands, catching whatever was dropped through every time.

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