Keas are large alpine parrots from New Zealand. Intelligent and social, they have olive-green plumage, a red rump, and a long, curved beak. Keas produce a distinct warbling call, a “play call,” that sounds — and functions — much like a human’s contagious laughter. Scientists made recordings of captive Keas making warbling calls, then played them for wild Keas. They began playing harder and even engaged birds that hadn’t been playing. Hearing it seemed to put them in a playful mood, even when they were alone.

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