Since the birds in the study did not join in play that was already underway, the researchers do not think the call is an instruction to become frisky. Instead, they concluded that it induces playfulness due to its acting as a positive emotional contagion. This, in turn, could promote tolerance and sync up moods when an individual is interacting with others.
Since many other birds and animals play, it is possible that other species produce emotionally contagious laugh-like calls too. Some of the sounds may even be out of a range that humans can hear. Rats, for example, produce laugh-like vocalizations in ultrasound.
Laughter can come with a price, however. Playful animals are usually inattentive, so emitting sounds would draw even more attention to them at a time when they are already vulnerable to predators. Kea are vulnerable to extinction due to habitat loss and other human-related problems, but these birds actually have few other predators. This could help to explain why they evolved their own form of laughter.
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Emotionally contagious sounds are not always happy ones, though.
"Negative emotional contagions have been found in many more cases than positive ones," Schwing explained. "Alarm calls and aggressive growls, for example seem to have an emotionally contagious effect on the receiver."
Even sadness can be contagious, at least in humans. He noted that people might tear up watching others cry, or while listening to sad music at a movie. The shared misery perhaps helps us to empathize and therefore bond more with others, helping to explain the evolutionary benefit.
The scientists hope to determine more specifically how play and related calls help social animals, be they parrots or humans.
"If the theory holds true that they increase tolerance in groups," Schwing said, "then one could argue that humans could learn from this by adopting play and/or laughter as a form of social facilitation."
Top Photo: Two juvenile kea tussle playing on the ground. Credit: Raoul Schwing