The concept of counting is beyond most animals - but not hyenas, new research shows.Sarah Benson-Amram and colleagues from Michigan State University played recorded calls of unknown hyenas to members of hyena clans in Masai Mara National Reserve in Kenya. Unknown hyenas are seen as potential intruders, so the ability to count their numbers and understand the size of the potential threat would be useful in determining whether to fight or back down.Wild hyenas responded differently to the playback of one, two, or three unknown hyenas. The authors suggest that this counting ability, unusual in the animal kingdom, evolved as a way to keep tabs on their social groups.Hyenas are fascinating and complex animals that live in sophisticated, hierarchical societies. Hyenas are able to keep track of the social statuses of the up to 90 members of their clan,  and remember which hyena belongs to which distinct subgroup. The size and complexity of hyena societies are similar to those of some primates. Researchers are looking to hyenas to test the social intelligence hypothesis, the idea that complex societies necessitate the evolution of increased intelligence.