Like most animals, vervet monkeys make a lot of different noises. As researchers, we often lump different vocalizations into various different signal “types”, eg., screams, barks, grunts, etc. Still, it’s difficult for researchers to determine whether all signals of a given “type” are created equally. For instance, does an infant’s scream always affect the behaviour of their mother in the same way, or, are there different screams that have a greater or lesser impact on a mother’s behaviour? A human example may make this concept a little easier to understand. For example, it’s likely that many mothers would agree that something about the sound of their own child’s cries gives them a clue as to the severity of their child’s situation. A human toddler that is simply screaming for more attention likely sounds different to a human toddler that is screaming because it has hurt itself, or is in some sort of danger.
While it is pretty clear that this sort of non-linguistic communication exists in human vocal signaling, it’s interesting to consider whether or not it exists in other animals. One way of addressing this question is to use what’s called a playback experiment. Over the course of the last several months, we have been making audio recordings of the vocalizations produced by our vervets on a daily basis. Using these recordings, we can play back vocal signals with different acoustic properties to the vervets to determine whether, for instance, a mother is more likely to attend to her infants screams when they are louder and longer, or whether these features of the signal are irrelevant. This experimental procedure can be extended to explore all sorts of vocal signals, including alarm calls, calls made when two groups meet, or even the casual grunts given between different monkeys as they pass each other. What’s most exciting about this is that it can give us some insight into to the early origins of non-linguistic communication in humans. We’ve only just started with our playback experiments here on Samara, but we’re excited to see what we can find by experimentally “talking” to these animals.
Until next time,
Picture: A baby is crying while being ignored by their mother.
