While it makes sense for an animal to be able to communicate well with other members of the same species, it is a little more unusual for the same to occur between species. This can be observed in some animals, especially if they form mixed-species associations, like in West African Diana monkeys (Cercopithecus diana) and Campbell’s monkeys (Cercopithecus campbelli). Both of these species have males that sound out alarm calls that differ for leopards and crowned eagles. A study was carried out to observe the ability of Diana monkeys to respond to Campbell’s alarm calls and if they can interpret the information being given by the calls.
An article published in May 2000 by Klaus Zuberbühler described the methods and findings. The monkey subjects inhabit the Tai forest of Cote d’Ivoire, where the research subsequently took place between June 1996 and February 1999. The experiments were field playback experiments that were divided into two large questions: “do Diana monkeys respond to Campbell’s alarm calls?” and “do Diana monkeys understand the meaning of Campbell’s alarm calls?” (Zuberbühler, 2000, 714).
The research involved playing out shrieks of a crowned eagles and growls of leopards in the vicinity of the monkeys. The responses of the monkeys to the calls were then recorded, usually in the form of their own resulting alarm calls.
Experiment 1 compared the responses of Diana monkeys to Campbell monkeys alarm calls. The researchers played out vocalization of Campbell monkeys reacting to crowned eagle shrieks and leopard growls. The playback of the Campbell monkey called were controlled for the number of calls and the duration. According to Zuberbühler (2000) Diana monkeys responded to recording of Campbell monkey’s leopard or eagle alarm calls accurately. They responded to eagle alarm calls by emitting their own eagle alarm calls but no leopard alarm calls. Similarly they responded to leopard alarm calls by emitting leopard calls and not eagle calls.
The second experiment investigated the ability of Diana monkeys to interpret the content of the Campbell monkey alarm calls. These monkeys heard Campbell monkey alarm calls, 5 minutes of silence, and then eagle shrieks or leopard growls. The monkeys had been previously primed with the corresponding alarm calls, and should thus have reacted weakly to the same call if they understood the meaning, just as they would if they had been presented with the same predator twice. Zuberbühler (2000) found that the monkeys were able to utilize the meaning in the Campbell monkeys alarm calls and appropriately gauge the threat of a predator.
The results of this study supported the hypothesis that, “non-human primates are able to use acoustic signals of diverse origin as labels for underlying mental representations” (Zuberbühler, 2000, 717). Also that this inter-species communication arises as a result of predatory pressures. While it is often assumed that members of the same species or group have effective communication, there is a great advantage to communication between hetero-specifics, which is why anti-predator behaviour can be observed following alarm calls between them. This study was also able to illustrate how the meanings of certain calls can be based on arbitrary signals, quit like how humans assign words to different meanings. This study emphasized the importance of the meaning over the acoustic features of cues in how a subject would react, supporting the idea that humans are not outstanding in their ability to do as a species.
Works Cited:
Zuberbühler, Klaus. (2000). Interspecies semantic communication in two forest primates. Proc. R. Soc. Lond. B (267), pg.s 713-718. DOI: 10.1098/rspb.2000.1061
