New Zealand's highly intelligent kea parrot has a human-like infectious laughter - a 'play call' that puts other birds around them into a playful mood, a new study has found.
The findings make kea the first known non-mammal to have such an "emotionally contagious" vocalisation, joining the ranks of humans, rats and chimpanzees.
Kea are known for their intelligence and curiosity, both vital to their survival in a harsh mountain environment.
"We were able to use a playback of these calls to show that it animates kea that were not playing to do so," said Raoul Schwing of the Messerli Research Institute in Austria.
"The fact that at least some of these birds started playing spontaneously when no other birds had been playing suggests that, similar to human laughter, it had an emotional effect on the birds that heard it, putting them in a playful state," said Schwing.
Schwing and his colleagues got interested in this particular call after carefully analysing the kea's full vocal repertoire.
It was clear to them that the play call was used in connection with the birds' play behaviour. That made them curious to know how kea in the wild would respond to the recorded calls.
The researchers played recordings of play calls to groups of wild kea for a period of five minutes. They also played other kea calls and the calls of a South Island robin as controls.
When the birds heard the play calls, it led them to play more and play longer in comparison to the other sounds.
"Upon hearing the play call, many birds did not join in play that was already underway, but instead started playing with other non-playing birds, or in the case of solitary play, with an object or by performing aerial acrobatics," the researchers said.
"These instances suggest that kea were not 'invited' to play, but this specific call induced playfulness, supporting the hypothesis that play vocalisations can act as a positive emotional contagion," they said.
While it might be a bit anthropomorphic, researchers said, the kea play calls can be compared to a form of infectious laughter.
The researchers said that they now plan to explore the effects of play and play calls on kea social groups more generally.
Earlier studies had made similar findings for chimpanzees and rats, they said.
The study was published in the journal Current Biology.