Back then, he was working as a research assistant in the Galapagos Islands, and he'd often pass by nests on the ground made by large white and black seabirds called Nazca boobies. He'd invariably see nests with two chicks inside, a big chick and a little chick but then the little one would disappear. 'Always. And I would frequently find it a meter, half-meter away from the nest site, just dead on the ground, apparently unrescued by the parents,' says Anderson.
These deaths turned out to be siblicide, the murder of one sibling by another. And in this species, the killing was the kind of routine practice that researchers now call 'obligate' siblicide, to distinguish it from the kind of less-frequent intra-nest murder that can occur in some species when food is scarce.
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