RESEARCH: Orangutans scratching is contagious

Contagious behaviour occurs when someone sees a behaviour and then does the same behaviour involuntarily as a reflex action. For example, if we see someone yawn, we yawn. We say that yawning is contagious. 

Scientists have found that orangutans scratch as an involuntary reflex when they see another orangutan scratch. 

Scientist Daan Laméris and a team of researchers studied Bornean Orangutans (Pongo pygmaeus).

Bornean Orangutan

They found that in Bornean Orangutans scratching is contagious when they see another member in the group scratch themselves. Orangutans were more likely to conduct contagious scratching if they see a stranger do it—that is, if the scratcher is not a member of their family. Also, Bornean Orangutans were more likely to scratch when seeing a stranger scratch in a tense situation. The researchers found that Bornean Orangutans scratch within 90 seconds after the triggering scratch. 

This is different from human yawning experiments because humans yawn more easily when they see family and friends yawn. 

The scientists observed 9 adult Bornean Orangutans (3 males and 6 females) ranging from 7-52 years old at the Apenheul Primate Park in The Netherlands from February to May 2017. 

Orangutans showed increased scratching rates after seeing a group member scratch, indicating behavioural contagion. The finding that scratching contagion was stronger when seeing strangers scratching than when seeing family members or friends scratching is a new observation for scientists. They think it occurs to promote group coordination and social cohesion.

Usually scientists have observed scratching contagion between a mother Orangutan and her infant to signal coordinated joint travel. It also occurs in family and friend groups to perhaps signal social distress, which reduces aggression. 

In this current experiment, the researchers know that stressed individuals often behave unpredictably, especially strangers. Therefore, increased awareness of a stressed stranger nearby, through scratching behaviour contagion, might be a way of preparing the observing Orangutans for unpredictable behaviour. Copying the scratching behaviour might suggest emotional contagion, and might lead to increased social cohesion and decreased aggression.

However, the scientists think that scratching is a complex behaviour in Bornean Orangutans, and that the degree of scratch contagion may depend upon many factors and types of social relationships. 

Bornean Orangutan
Bornean Orangutan
Bornean Orangutan

Reference: Low relationship quality predicts scratch contagion during tense situations in orangutans (Pongo pygmaeus), Daan W. Laméris, Evy van Berlo Elisabeth H. Sterck, Thomas Bionda, Mariska E. Kret, 24 April 2020.

[Location of photographs: Paris Zoo, France]

Photographer: Martina Nicolls


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