Bird contagionThis week, scientists report that New Zealand parrots can spread positive emotion, too — or at least behaviour that could indicate their state of mind. The researchers recorded the play calls of keas (Nestor notabilis) and played them back to groups of wild keas. When the birds heard the sounds, they played more vigorously and longer — certainly more than when they heard the calls of a South Island robin (Petroica australis). The calls did not, however, seem to act as an invitation to join existing birds at play. Some keas that heard them preferred to start their own play — typically embarking on feats of aerial acrobatics. With self-confessed anthropomorphism, the scientists suggest that the play calls of these birds act in the same way as infectious laughter in people (R. Schwing et al. Curr. Biol. 27, R213–R214; 2017). In its homeland, the playful kea is called the clown of the mountains. And as every good clown knows: cry and you cry alone. But laugh and the world laughs with you.