Black howler monkeys (male left, female right) are known for the piercing call with which they attract attention at dawn.
Thanks to specialised membranes in their larynx, New World monkeys in particular turn out to be masters at incorporating voice breaks into their calls.
The best yodellers come not from the Tyrol, but from the rainforests of South America. New World monkeys produce ‘ultra-yodels’ that can encompass frequency jumps up to five times greater than those of human yodels. Whilst human yodellers reach at most one musical octave, South American monkeys achieve more than three octaves. This emerges from an analysis of CT scans, computer simulations and fieldwork led by British evolutionary biologists on the calls of primates in the Bolivian nature reserve La Senda Verde (Philosophical Transactions of the Royal Society B, 3 April). The species studied include the black howler monkey (Alouatta caraya), the tufted capuchin (Sapajus apella), the Bolivian squirrel monkey (Saimiri boliviensis) and the black-faced black spider monkey (Ateles chamek).
It was already known that monkeys and apes possess specialised vocal membranes that have been lost in humans, probably to enable more stable speech. This study has established for the first time that these extremely thin membranes, situated above the vocal cords in the larynx, allow monkeys to introduce voice breaks into their calls by switching their sound production from the vocal cords to the vocal membranes. The resulting call has the same rapid frequency transitions as those of yodellers in the Alps or the famous jungle call of Tarzan, but spans a far greater frequency range. It has likely evolved to enrich the monkeys’ vocal repertoire and to attract attention or signal identity.
See also:
–Yodeling Monkeys: The Surprising Vocal Range of New World Primates – website of the University of Vienna, 3 April 2025
–Monkeys are world’s best yodellers – new research – website of Anglia Ruskin University – 3 April 2025