 However, Bullinger, Melis, and Tomasello showed that chimpanzees actually exhibit a preference for working alone, unless cooperation is associated with higher pay-offs .Captive spotted hyenas ("Crocuta crocuta"), social carnivores that hunt in groups, have cooperated to obtain food rewards by pulling ropes in an experimental setting.Mimicking the natural choice hunting hyenas face when deciding which of many prey to jointly attack, researchers Drea and Carter set up two devices instead of one, as previously used in all cooperative pulling tasks with other species.