New insight into monkey warning calls
Pic caption – Diana monkey in the Tai Forest, Ivory Coast.
Forest monkeys warning their offspring of an impending attack use similar techniques to humans to affect the meaning of some of their warning calls.
During a study in the Tai National Park on the Ivory Coast,
the largest remaining area of primary forests in West Africa, Dr Klaus Zuberbuhler from the University of St Andrews’ School of Psychology monitored two species of monkey – the Campbell’s monkey and the Diana monkey – both of which are under threat of poaching, deforestation and, ultimately, extinction.
Dr Zuberbuhler revealed that, in potentially dangerous situations, the male Campbell’s monkeys produce a “boom” noise before giving a distinct alarm call. The alarm call given depends on the nature of the suspected predator – for example, different calls are given for a suspected leopard or crowned-hawk eagle, two of their main predators.
This “boom” devalues the alarm call and is used in situations where the monkey is unsure of the exact nature of the attacker but still wishes to alert its offspring. It is thought that the use of the “boom” could be compared to man’s use of the word “maybe” or “perhaps.”
The study, published in the latest edition of “Animal Behaviour”, was undertaken through playback experiments – recording different alarm calls and playing them back in the absence of the predator to test the monkeys’ response.
Dr Zuberbuhler said, “Judging from the Diana monkeys’ responses to the playback stiumuli, the booms actively modified the meaning of the subsequent alarm call series and transformed them from highly specific predator labels, requiring immediate anti-predator responses, into more general signals of disturbance that do not require any direct responses. There are interesting parallels between their communication system and some human linguistic phenomena. For instance, terms like “maybe” or “kind of” have comparable semantic effects on subsequent sentence structures as the booms have on the subsequent alarm calls. Although the analogies to human language remain suggestive, the results show that monkeys can understand and implement the same sentence structure rules that humans use.”
Dr Zuberbuhler, who believes that the ability to take preceding signals into account is probably widespread in the animal world, hopes to embark on another species from the Tai National Park later this year, the Sooty Mangabeys (Cercocebus atys).
Covering over 450,000 hectares, the Tai National Park has a mean annual temperature of 240C, a mean annual rainfall of 1,830 mm and a distinct dry season from December to January and is classified as a tropical moist forest.
Campbell’s monkeys are a drab- coloured, well-camouflaged monkey based in the lowest level of the rainforest where they feed on fruits and insects. Group sizes are small – between 8 and 15 individuals – and include a single adult male, a handful of adult females and their offspring.
Diana monkeys, on the other hand, are brightly coloured, handsome and noisy and are the most active foragers in the forest and the most distinctive species at Tai. Groups consist of approximately 20 individuals – one adult male, a number of reproducing females and their offspring. Because of their foraging behaviour throughout all forest layers as well as their high vigilance levels, these monkeys are extremely observant and excellent look-outs for predators.
For further information on the Tai Monkey Project, visit website – http://www.mpi- seewiesen.mpg.de/~knauer/noe/taan.h tml.
For further information on the School of Psychology – recently awarded a 5*(a) rating in the 2001 Research Assessment Exercise – visit website – http://psy.st- and.ac.uk/.
NOTE TO EDITORS – To contact Dr Zuberbuhler, please call 01334 462080. Emailable photographs of the monkeys/forest are available from Claire Grainger – contact details below.
Issued by Beattie Media on behalf of the University of St Andrews For more information please contact Claire Grainger on 01334 462530, 07730 415 015 or email [email protected] Ref: monkeys/standrews/chg/18feb2002