A playful parrot has an infectious laugh that influences the behaviour of its feathered friends, scientists have discovered.
The "play call" of the kea parrot, from New Zealand, 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.
Transformed by the sounds, the birds performed joyful aerobatics, played chase games, tossed objects around and kicked up their feet.
Scientists believe it is evidence of the kind of emotional contagion normally associated with irrepressible young children.
Lead researcher Dr Raoul Schwing, from the Messerli Research Institute in Austria, said: "We were able to use a playback of these calls to show that it animates kea that were not playing to do so.
"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.
"If animals can laugh, we are not so different from them."
Kea parrots 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.
To carry out their investigation, the scientists recorded the sound and played it back to wild birds at Arthur's Pass National Park, on New Zealand's South Island.
Hearing the call had an immediate and dramatic effect. Keas of both sexes spontaneously began playing on their own or with each other.
Examples of 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.
Often, one or more of the birds would launch into a display of aerial acrobatics that involved high-speed dolphin dips, loops and spirals, or showed off their skill at hovering in updrafts.
"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.
The scientists wrote in the journal Current Biology: "As with human laughter, the kea's play call could act as a positive emotional contagion towards conspecifics (other members of the same species)..
"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.
Previous research has shown that deaf rats are less likely to play than rats with normal hearing, but not being able to see does not have the same effect.
Play is thought to strengthen bonds between social animals, which has benefits such as food sharing.
Adult play between males and females is also linked to courtship in primates and dogs.