Long term projects like ours allow us to follow individuals as they grow, and mature over time. One aspect of animal growth we have recently turned our attention towards is the development of our vervet’s vocal repertoires. Vocalizations are interesting in this respect, because as humans, our vocal repertoires often change as a result of learning. As children, we learn different words in whatever language(s) we are exposed to, and we subsequently learn to link those words into sentences. Because vocal learning is so important to how humans communicate verbally, it’s easy to assume that non-human animals “learn” how to communicate vocally as well.
Alternatively, it’s likely that a lot of the sounds produced by non-human animals are basically pre-programmed at birth. This being the case, the gradual changes in the sounds we observe as researchers are likely the product of something much simpler than learning; namely growth. When an animal is born, it is much smaller than it will be as an adult, and compared to an adult, the muscles in its vocal tract are relatively undeveloped. These differences put physical constraints on a young individual’s ability to produce the sounds that an adult does, and it is therefore very likely that a lot of the differences in the vocal repertoires of young versus adult animals can be explained without the need to evoke “learning” as a mechanism.
Because the structure of a vocalization is largely influenced by the size of the animal that is producing it, we Verveteers can broach a somewhat complex question; do our vervets’ vocalizations change as they grow because they are learning to communicate vocally, or because they are simply growing in size? On Samara, we take regular measurement of our subjects’ weights as a means of tracking their physical development. Using this data, we can compare a vervet’s body size to audio recordings of their vocalizations we make as they grow. Basically, if the changes we hear in vocalizations of vervets at different life stages can be explained by physical development, we should see a predictable relationship between body size, and the sounds an animal can produce. If however body size and vocal structure are not predictably related to one another, it is possible that other mechanisms, such as learning, may play a larger role. Pretty cool, eh?
Until next time,
Colin and the Verveteers
The Vervet Monkey research project is a collaboration between a number of international universities. The project has been based at Samara Private Game Reserve in the Great Karoo since 2008. The aim of the project is to investigate the adaptations of these fascinating monkeys to climatic changes.
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