Monkeys and apes are the closest relatives to humans in the animal kingdom. While they cannot speak, some of them have special structures in their larynxes, enabling them to produce frequency jumps that sound similar to yodeling. This comparison to the Alpine cultural phenomenon is drawn by an international research team in the journal Philosophical Transactions of the Royal Society B, which analyzed the basis for this ability in certain species of monkeys.
With a range of up to three octaves, their frequency range is larger than that of humans, according to the findings. The study’s focus was on New World monkeys, such as tamarins, capuchins, and squirrel monkeys. These primates have thin, light membrane tissues at the top edges of their vocal cords that allow for these vocalizations, explained lead author Christian T. Herbst from the University of Vienna.
Monkeys Master Two Ways of Sound Production
“Humans have likely lost these membranes during evolution,” Herbst said. Their exact function had been unclear in previous research, and yodel-like sounds were only briefly mentioned. “For the first time, we have shown the link between anatomy and acoustic output,” said Herbst, a voice researcher.
The study used various methods, including non-invasive sound recordings taken at the La Senda Verde wildlife sanctuary in Bolivia. Experiments were also conducted on the larynxes of monkeys that had naturally passed away, and computer models helped further the analysis.
Benefits of the “Ultra-Yodeling” and Open Questions
Two types of vocalization were identified in the monkeys. The first involves only the vocal cords vibrating, similar to human vocalization. The second method involves the membranes vibrating as well, allowing for higher frequencies, leading to abrupt, yodel-like frequency jumps. While humans typically produce one octave of change, monkeys can span more than three octaves.
These findings could be beneficial for monkeys, as the irregular vibrations allow for more complex vocalizations and the communication of information without complex neural structures. In contrast, humans need a simple and stable sound source for complex communication.
The findings raise new questions about the use of “yodel-like” sounds in monkeys, which remain open for future research. The study suggests that these sounds are essential for primates with complex social lives and diverse communication needs.
