Some rats giggle when their bellies are tickled. Dogs wag their tails.
Animals express joy in different ways. But it's not always easy to figure out what animal expressions mean.
You can’t ask the animal, and you can’t look for those telltale signs in humans – a smile or crinkle around the eye – especially if the animal has completely different facial muscles, as is the case for kea.
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Professor Ximena Nelson from the University of Canterbury observed kea playing in the mountains – her first clue that New Zealand's alpine parrots can be joyful. From there, she and her team investigated the different calls that kea made, and then analysed the different behaviours of the kea as they made these calls, to try to discern their functions.
This proved extremely difficult, but one call did seem to be strongly linked to play – the warble call, or kea laughter as it is called.
Listen to the full episode to learn about kea laughter, as well as the how and the why of studying positive emotions in animals.