New Zealand's endangered kea has an infectious laugh that influences the behaviour of its feathered friends, New Zealand scientists have discovered.
Its "play call" puts other members of its species in the mood for fun, research has shown.
When deadpan parrots heard recordings of the distinctive "ha-ha" calls, they spontaneously started to party - performing aerobatics, playing chase games, tossing objects around and kicking up their feet.
"We were able to use a playback of these calls to show that it animates kea that were not playing to do so," said lead researcher Raoul Schwing, currently at the Messerli Research Institute in Austria.
He carried out the research while at the University of Auckland, co-supervised by Ximena Nelson of the University of Canterbury and Stuart Parsons, who was at the University of Auckland at the time.
"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."
Kea, the world's only alpine parrot, have a range of calls, but one in particular appears to be used in connection with the bird's complex play behaviour. It also sounds remarkably like a laugh.
The scientists recorded the sound and played it back to wild birds in Arthur's Pass National Park.
The call had an immediate and dramatic effect. Keas of both sexes spontaneously began playing.
Play included chase games on the ground and in flight, mock fights and tussles, foot-kicking and repeatedly tossing the same object in the air.
"Control" sounds in the form of calls from a South Island robin, two other types of non-play kea call, and an artificially produced tone did not elicit the same response.
"As with human laughter, the kea's play call could act as a positive emotional contagion towards conspecifics (other members of the same species)," the scientists wrote in the journal Current Biology.
"In anthropomorphic terms, kea play calls act as a form of infectious laughter."
Contagious "laughter" has also been reported in non-human primates, such as chimpanzees, and rodents.
Play is thought to strengthen bonds between social animals, which has benefits such as food sharing.