Monkeys are the best yoderers in the world, find “voice break” analysis

New research has found that the world’s most incredible yodelers are not from Austria or Switzerland, but from the tropical rainforests of Latin America.

Published in the Journal Philosophical Transactions of the Royal Society B and led by experts from Anglia Ruskin University (ARU) and the University of Vienna, the study provides important new insights into the diverse sounds of voices of nonhuman primates, revealing for the first time how certain calls are generated.

Apes and monkeys have special anatomy in their throats, known as the vocal membrane. This disappeared from humans through evolution to allow for more stable speech. However, the exact benefits these offer to non-human primates were previously unknown.

A new study found that these vocal membranes are very thin and sitting on the folding of the voices of the larynx, allowing monkeys to introduce “voice destruction” to their calls.

These speech cuts occur when a monkey switches sound generation from voice folding to vocal membranes. The generated calls have the same rapid transitions at frequencies heard by the famous cry of alpine yodel or Tarzan, but cover a much wider frequency range.

This study included CT scans, computer simulations and fieldwork analysis at the La Senda Verde Wildlife Refuge in Bolivia. There, the researchers recorded and studied the invocations of various primate species, including the black and gold Howler monkey (Alouatta Caraya), Tufted Capuchin (Sapajus Apella), Black-Capped Squirrel Monkey (Saimiri boliviensis), and Peruvian Spider Monkey (Ateles chamek).

The range from Mexico to Argentina has been found to have evolved the largest vocal membranes of all primates, suggesting that these thin tissue ribbons play a particularly important role in the repertoire of vocal production and calling.

This study revealed that the “super yodel” produced by these monkeys can jump five times more frequencies than the frequency changes possible in a human voice, allowing human yodels to exceed three musical octaves while human yodels are usually less than one octave.

“These results demonstrate how monkeys utilize the evolved features of the larynx in various ways,” said Dr. Jacobdan, an associate professor of evolutionary biology at Anglialuskin University (ARU) in Cambridge, England.

“This could likely be used to enrich the animal’s repertoire of appeal, as it could be used to change attention, diversify, or identify oneself.”

“This is an attractive example of how nature offers a means to enrich animal vocalization despite the lack of language,” said Christian T. Herbst, PhD, lead author of the Faculty of Behavior and Cognitive Biology at the University of Vienna.

“The production of these complex vocal patterns is mostly possible in a way in which the larynx of an animal is anatomically shaped and does not require the complex neural control produced by the brain.”

Professor Tecumse Fitch, an expert on the evolution of human voices at the University of Vienna and a co-author of the study, said, “Our research shows that the vocal membrane not only expands the pitch range of monkeys, but also destabilizes its voice. They may have been lost during human evolution and promoted the stability of the pitch of song and speech.”

Experts from Anglia Ruskin University and the University of Vienna, Osaka University, Ritumaikan University in Japan, KTH Royal Institute of Technology in Sweden, and La Senda Verde Wildlife Sanctuary in Bolivia contributed to the research.