Orangutans have so much in common with humans that their name, as Malaysians know, literally means “forest person”. One of these is their ability to produce several sounds simultaneously, not unlike songbirds as well as some human musicians.

Researchers at Britain’s University of Warwick made this discovery after tracking two groups of orangutans on the islands of Borneo and Sumatra over 3,800 hours. They found that these apes, which are native to Asia, sometimes produce several vocal sounds at the same time.

For example, large male Bornean orangutans have been seen to produce sounds called “chomps”, which are described as “bubbly calls”, in combination with “grumbles”, which sound like a starting engine.

These two types of vocalisations are produced in combination in combative situations to intimidate opponents and assert dominance, the biologists explain in their study published in the journal “PNAS Nexus”.

Female Sumatran orangutans were observed making “kiss-squeaks”, which sound like a human kissing noise, at the same time as long, low “rolling calls”. They produced these two sounds simultaneously to alert other orangutans to the presence of a potential predator.

This discovery highlights the complexity of orangutan language. Biphonic behaviour – the ability to produce two sounds simultaneously – is an acoustic phenomenon rarely observed in the animal kingdom. Horses, elk and songbirds have this ability, as do human beatboxers.

“Humans use the lips, tongue and jaw to make the unvoiced sounds of consonants, while activating the vocal folds in the larynx with exhaled air to make the voiced, open sounds of vowels,” explained lead study author Dr Adriano Lameira.

Researchers believe that the vocal-control and -coordination abilities of apes have been underestimated, unlike those of birds. While birdsong resembles human language in some respects, their anatomy differs greatly from ours, which makes it difficult to establish direct links between birdsong and the evolution of human language.

The fact that orangutans are able to produce two sounds simultaneously suggests that this vocal ability is part of great ape behaviour and, therefore, of our common ancestors.

“Now that we know this vocal ability is part of the great ape repertoire, we can’t ignore the evolutionary links,” Lameira added.