The clever calls of nature
Scientists have discovered that birds are capable of recognising calls that other species use to warn each other about predators.
Not only that, but certain species are able to tell one warning call from another, learning to ignore those which did not indicate a danger to them.
The biologists at the University of St Andrews have found a particular bird species that recognised and responded to threatening noises from a potential predator as well as warning calls from other animals under threat from the same predator.
Hugo Rainey spent eighteen months in West Africa studying wild hornbills, in collaboration with fellow biologist Professor Peter Slater and primatologist Dr Klaus Zuberbühler.
The key to Hugo’s research lay in the interaction between the hornbill and the Diana monkey, a brightly coloured species which is extremely observant and therefore an excellent look-out for predators. Dr Zuberbühler first noticed that large hornbills were often present in the vicinity when he studied the alarm calls of the Diana monkey. With their loud calls carrying for around two kilometres, they often came close to obscuring the monkey calls on his recordings.
The Diana monkey is preyed upon by the crowned eagle and the leopard and has a distinct warning call for each. It only shares one of these predators – the crowned eagle – with the hornbill, raising the question of whether the birds respond to one of them but not the other.
To answer the question, Hugo tested different flocks of yellow- casqued hornbills – a near- threatened species – in the Ivory Coast’s Taï Forest to see how they responded to the monkey calls. He found that not only did the hornbill respond to shrieks from the eagle itself, but it only responded to the eagle warning calls from the Diana monkey. It did not respond to the threatening growls of the leopard or to the Diana monkey’s leopard warning call.
“We presume that the hornbills did not respond to the Diana monkey’s warning call about the leopard, because the leopard is not a threat to them. This demonstrates how capable birds are of obtaining relevant information about predators from the calls of other species,” said Hugo.
The hornbills responded by increasing the number of calls they make, which are likely to act as a warning to fellow hornbills. They may also benefit from warning the monkeys and from indicating to the predator that it has been spotted. This may pay dividends, as predators tend not to return to the same place if they have been unsuccessful.
The results of Hugo’s research are thought to be the first time that a bird species have been found to distinguish between threatening noises from different animals and the first time that a bird has been shown to distinguish between the alarm calls of a mammal species. Some mammals can distinguish between and respond appropriately to the alarm calls of other mammal and bird species, for example Campbell’s monkeys in Ivory Coast to different Diana monkey alarm calls and vervet monkeys in Kenya to the different alarm calls of superb starlings. However, the ability of birds to distinguish between mammal alarm calls has not been previously investigated.
To add further challenge to Hugo’s task, halfway through his PhD in early 2002, he found out that the hornbills he had been tracking had migrated somewhere else. This phenomenon, which was unheard of, caused him a few problems.
“Instead of finding 3-4 groups a day, I was finding one every 3-4 days. This made my work much harder as you might expect. So much harder that I exhausted myself walking 25 km in the forest every day looking for them and also fell ill with malaria in May 2002,” he said.
“I planned to return in October 2002 and on the day in mid-Sept I was booking my flight out, Ivory Coast descended into a civil war in which thousands of people were killed. On top of that, opportunistic rebels invaded from Liberia into the area around Taï Forest. Unsurprisingly, it was unsafe for me to return. This caused a few problems for my work, but luckily I had enough data to complete this particular study.”
Hugo, now back in St Andrews, will complete his PhD in spring this year and following that hopes to work in Central Africa managing a national park.
PICTURE CAPTION: Top row (L-R): The Hornbill and the Diana monkey Botton row (L-R): Leopard and crowned eagle. CREDIT: Ben Wang, Dr David Jenny and the Peregrine Fund.
NOTE TO EDITORS:
THE RESEARCHERS ARE AVAILABLE FOR INTERVIEW:
The paper ‘Hornbills can distinguish between primate alarm calls’ by Hugo J. Rainey, Klaus Zuberbühler & Peter J.B. Slater will be published in the April edition of Proceedings of the Royal Society B.
It will be available online from 3rd March at: http://www.journals.royalsoc.ac.uk/ openurl.asp?genre=issue&eissn=1471- 2954&volume=preprint&issue=preprint
NOTE TO PICTURE EDITORS:
EXCELLENT QUALITY JPEGS OF HORNBILLS, DIANA MONKEYS, LEOPARDS AND CROWNED EAGLES ARE AVAILABLE FROM THE PRESS OFFICE – CONTACT DETAILS BELOW.
SOUND FILES OF THE HORNBILLS AND THE DIANA MONKEYS ARE ALSO AVAILABLE FROM THE PRESS OFFICE. SOUND FILES OF LEOPARDS AND CROWNED EAGLES ARE AVAILABLE FROM http://www.bl.uk/collections/sound- archive/wild.html Tel 020 7412 7402/3, Fax 020 7412 7441, Email: [email protected]
Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050 103, or email [email protected] Ref: Hugo Rainey bird call 030304 View the latest University news at http://www.st-andrews.ac.uk