Have you ever adopted a local accent so people can understand you better? Some tamarin monkeys in the Amazon rainforest do something similar if they share living space with a closely related species.
Red-handed tamarins seem to have changed their calls to sound more like those of pied tamarins, so that the two species can warn each other away from their respective territories.
Tamarins use long, high-pitched whistles to alert other individuals to their presence and deter them from getting too close. “Nobody wants to get into a fight. You scream and shout a bit first to warn each other,” says Jacob Dunn at the University of Cambridge, who was involved in the research. “It’s a means of maintaining space between groups.”
Pied tamarins (Saguinus bicolor) have a pure-sounding note, while in most of the Amazon, the calls of red-handed tamarins (Saguinus midas) are similar but span a wider frequency range.
Tainara Sobroza at the National Institute of Amazonian Research in Manaus, Brazil, wondered if the two species’ calls would sound even more similar in the patch of forest where they overlap. Her team recorded calls from the monkeys at 15 sites that were either in overlapping habitat or in places where only one species lived.
In the shared territory, although the pied tamarins hadn’t changed their calls, the red-handed tamarins had shifted to a slightly purer whistle, a difference that could be measured when the sounds were translated into a spectrogram, a visual representation of sound. “It is like an accent because they’re giving the same message, but saying it in a slightly different way,” says Dunn.
The change in calls is seen only among tamarins living in pristine old-growth forest, not in places where trees have previously been cut down and the regrowing vegetation is less mature, with fewer thick tree trunks, and so transmits sound differently.
Convergence of animal calls has previously been seen among different birds that share habitats, but this is the first such case recorded in primates.
Journal reference: Behavioral Ecology and Sociobiology, DOI: 10.1007/s00265-021-03028-x
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