the pair plans to test kea to find out whether warbling might shift the birds’ mental state to make them more optimistic, as laughter does for us. This may seem like anthropomorphizing, projecting human experience onto an animal’s behavior, but it turns out there is a solid, well-established test for optimism in animals. Here’s the kea version: The bird is taught that a big box always contains food and a little one does not. Then a midsize box shows up. “An optimistic animal will take a ‘glass half-full’ perspective,” says Taylor, “and assume that the medium box is like the big one and will
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