Hearing laughter can make people laugh, and it seems that kea parrots react similarly, displaying play behaviour after hearing a particular call from fellow birds. This makes them the first non-mammals known to experience 'contagious' merriment.
Raoul Schwing, now at the University of Vienna, and his colleagues studied kea parrots (Nestor notabilis; pictured) in the wild in New Zealand. They played a warbling sound that is made by the birds and associated with playful behaviour, for five minutes at a time. The researchers found that the animals played more often and for longer periods of time when they heard the warble than when they heard non-play kea calls, the tweets of a local robin or an artificial tone. Play stopped shortly after the sound ceased.
The authors conclude that the call is not a courtship invitation but stimulates playful emotion.