Vocal production and auditory learning in the genus Chlorocebus
Final Report Abstract
A central objective fueling research on the vocal communication of nonhuman primates is to reveal the origins of semantic communication. A second influential research stream aims to characterize the biological function of animal vocalizations and thus seeks to comprehend which advantages are conferred to signalers who produce a particular call types in certain contexts. Vervet monkeys (Chlorocebus pygerythrus) have been an important model system for both research streams and their alarm call system has become the paradigmatic case of semantic communication in animals. While ample research has probed what ‘meaning’ these calls have for individuals and how this meaning is acquired, we know little on how individuals vary in their call usage. Our project filled this gap with a two year field study on free-ranging vervet monkeys. In our first study, we focused on the loud calls of adult males that were assumed to be predominantly produced towards land predators like leopards. We investigated whether males differed in how often they called, whether call rates changed in the mating season and whether loud calls occurred outside of predator contexts. We found that loud calls were most frequently produced by the highest-ranking males, were uttered more often during the mating season and often occurred in aggressive contexts, indicating that loud calls do not exclusively indicate predators but also signal individual competitive ability. Our study thus illuminated a previously overlooked function of this call type and thereby also enriches our understanding of the possible meaning these calls may have for other monkeys, contributing to ongoing research on the semantic content of primate vocalizations. Our second study focused on the monkeys´ responses to snakes, a constant threat in their natural environment. We investigated whether demographic factors like age and sex affect individual responses and whether monkeys discriminate among different snake species. We found that adult males were less likely to approach snakes compared to adult females and juveniles of both sexes. We further found that monkeys, on average, responded more strongly to pythons compared to other snake species. Since pythons are the only confirmed snake predators of vervet monkeys, our result thus suggest that the monkeys primarily distinguish predatory from non-predatory snakes and are not strongly sensitive to whether snakes are venomous or not. Our third study used drones as predator models to probe how monkeys categorize novel threats. This project had to be abandoned half way due to the Covid-19 pandemic, but we conveyed our experience in form of a review article on the use of drones to study animal behavior, in which we also discuss their use for population monitoring and conservation.
Publications
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Alarm barks of male vervet monkeys as vocal displays of male quality. Talk presented at 114th Meeting of the German Zoological Society, Bonn
Schad, L., Dongre, P., van de Waal, E. & Fischer, J.
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Alarm barks of male vervet monkeys as vocal displays of male quality. Talk presented at International Society for Behavioral Ecology Congress 2022
Schad, L., Dongre, P., van de Waal, E. & Fischer, J.
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Opportunities and risks in the use of drones for studying animal behaviour. Methods in Ecology and Evolution, 14(8), 1864-1872.
Schad, Lukas & Fischer, Julia
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Alarm barks of male vervet monkeys as displays of male quality.
Schad, Lukas; Dongre, Pooja; van de Waal, Erica & Fischer, Julia
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Alarm barks of male vervet monkeys as indicators of male quality. Talk presented at Behaviour 2023 conference, Bielefeld
Schad, L., Dongre, P., van de Waal, E. & Fischer, J.
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Animal Alarm Calls. Evolutionary Biology. Oxford University Press.
Schad, Lukas & Fischer, Julia
