Observed: Spotted hyena Crocuta crocuta
Counts: The number of hyenas on the recording, according to the study, which is the first to show that hyenas can distinguish one intruder’s whoop from another’s.
Calculates: Its odds before approaching the intruders or fleeing. “They’re more cautious when they’re outnumbered and take more risks when they have the numerical advantage,” says Sarah Benson-Amram. Hyenas join lions and chimpanzees as animals that demonstrate the ability to compare their own to their opponents’ numbers.