In this week’s Nature a report from Kate Arnold and Klaus Zuberbühler from the Scottish Primate Research Group demonstrates that the putty-nosed guenon can combine vocalizations in order to convey different meaning. The meaning is is found between alarm calls for different situations and contexts.
From the article:
Like most forest guenons, male putty-nosed monkeys (Cercopithecus nictitans) produce two acoustically distinct loud calls (‘pyows’ and ‘hacks’) in response to a range of disturbances. Males also call spontaneously, especially during morning foraging and evening travel to sleeping sites. In addition, these calls can function as alarm calls to warn the group of an approaching predator and to discourage attack: pyows are used primarily when a leopard (Panthera pardus) is in the vicinity, and hacks are produced mainly in response to crowned eagles.
In addition to these calls, the researchers found that males often combine the same two calls into a third structure, a ‘pyow–hack’ (or P–H) sequence. The P-H sequence was emitted either to threats of leopards or eagles. In response to these calls the group of guenons respond by beginning to move. So, calls for either P or H did not significantly get the group moving. But P-H calls did.
Arnold and Zuberbühler went further on by playing different sounds to the groups (there were 17 guenon groups studied in all). Each group consisted of several adult females and one male (…hmm…).First, leopard growls were played to the group. In over half of the groups the male responded with P-H calls. In the other groups the males did call, though not with the P-H sequence.
Now wait a minute! Is this really something worth reporting in Nature? Evoking specific alarm calls in only half of the groups is not normally seen as powerful statistics. But hold on; here’s the neat part of this study. The researchers used a GPS to locate where the groups were as they moved (they are easy to locate by the calls, then move to that location and look up the GPS location). Here it was found that the groups in which males expressed the P-H combination moved for significatly longer distances. Furthermore, the groups “response to P–H sequences was not confined to the predator context, but was generally related to whether the group moved”.
In other words, this study demonstrates that not only do these putty-nosed guenons display differential vocal expressions (in males) to threats. The expressions are interpreted differently according to the context (movement). Altough it is known that syntax sets human language apart from other natural communication systems, it is also agreed that the evolutionary origins of human language are obscure. The study by Arnold and Zuberbühler sheds light on the evolutionary building blocks of language.
If you have access to Nature, you can also listen to the calls (single or combined form) through the supplementary material.