Can Monkeys Yodel? Exploring Animal Vocalizations
The question of whether animals, particularly monkeys, can yodel is not straightforward and hinges on how yodeling is defined. Tecumseh Fitch, a bioacoustician at the University of Vienna and co-author of a recent study, notes that many animal vocalizations, including those of birds and toothed whales, exhibit sudden changes in pitch. A 2023 study highlighted that toothed whales can create various vocal registers using their nasal passages for both echolocation and communication purposes.
Research into vocal registers among non-human primates has been less extensive. However, findings suggest that certain calls made by primates share similarities with human vocal ranges. For instance, the “coo” of the Japanese macaque resembles a human falsetto, while the Syke monkey’s squeal aligns with what is known as the human “modal” voice. Additionally, the Diana monkey emits alarm calls that are comparable to the human “vocal fry” register.
Non-human primates possess an anatomical feature that has been lost in humans as evolution progressed: lightweight, thin vocal membranes situated just above the vocal folds. This anatomical attribute has sparked curiosity among scientists regarding its function. A 2022 study suggested that these membranes play a vital role in sound production. The authors of the current study aimed to investigate whether these membranes serve as an additional oscillator, potentially allowing non-human primates to replicate the diverse vocal registers observed in humans. This capability could hypothetically enable them to produce a wider array of vocalizations—possibly even yodels.
The research team examined various species, including black and gold howler monkeys, tufted capuchins, black-capped squirrel monkeys, and Peruvian spider monkeys. They utilized CT scans of removed larynxes from monkeys preserved at the Japan Monkey Center, along with two larynxes from tufted capuchins obtained at Kyoto University. Additionally, they captured live recordings of monkey vocalizations at the La Senda Verde animal refuge situated in the Bolivian Andes, employing non-invasive electrogoniometry to monitor the vibrations of the vocal folds.
