For this New Zealand parrot, 'laughter' is contagious

The findings make kea the first known non-mammal to have such an "emotionally contagious" vocalization, the researchers say. Earlier studies had made similar findings for chimpanzees and rats.

"We were able to use a playback of these calls to show that it animates kea that were not playing to do so," says 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."

Schwing and his colleagues got interested in this particular call after carefully analyzing the kea's full vocal repertoire. It was clear to them that the play call was used in connection with the birds' play behavior. That made them curious to know how kea in the wild would respond to the recorded calls.

To find out, the researchers played recordings of play calls to groups of wild kea for a period of five minutes. The researchers 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 write. "These instances suggest that kea weren't 'invited' to play, but this specific call induced playfulness, supporting the hypothesis that play vocalizations can act as a positive emotional contagion."

While it might be a bit anthropomorphic, they continue, the kea play calls can be compared to a form of infectious laughter. The researchers say that they now plan to explore the effects of play and play calls on kea social groups more generally.

For the rest of us, the findings come as an intriguing reminder: "If animals can laugh," Schwing says, "we are not so different from them."