Ability suggests intelligence evolved to keep track of social interactions :

Hyenas can count like monkeys

Hyenas can count up to three. Researchers playing recorded calls to the wily carnivores found that wild spotted hyenas (Crocuta crocuta) responded differently depending on whether they heard one, two or three individuals.

The result adds numerical assessment to the list of cognitive abilities that hyenas share with primates, and supports the idea that living in complex social groups - as both primates and hyenas do - is key to the evolution of big brains.

Sarah Benson-Amram, a zoologist at Michigan State University in East Lansing, and her colleagues played recordings of hyena calls, or whoops, to members of two hyena clans in the Masai Mara National Reserve in southwestern Kenya1.

The recordings were made in Tanzania, Malawi and Senegal, so the calls were unfamiliar to the Kenyan clans, and would have been interpreted as belonging to potential intruders.

The recordings each consisted of three bouts of whooping, from one, two or three different animals. In 39 trials involving resting adults mostly lone females - Benson-Amram measured how vigilant the animals became while the recordings were playing by comparing the amount of time they spent facing the speaker with the amount of time they spent looking away or resting.

Although some females became equally watchful in response to all of the recordings, most of the animals distinguished between one, two or three intruders, their attentiveness increasing with the number of unique calls they heard.

The finding is published in Animal Behaviour.

A similar ability has been shown before in lions (Panthera leo)2, chimpanzees (Pan troglodytes)3 and black howler monkeys (Alouatta pigra)4. But in most of those studies, the calls were all played at once, so the animals could simply have been responding to the total amount of noise in the chorus.

To avoid that, Benson-Amram played the calls consecutively - either repeating the same call or mixing whoops from two or three

individuals.

To work out how many opponents they faced, the listening hyenas not only had to remember how many calls had sounded overall, but also had to recognize whether they had heard each particular caller before.

Michael Wilson, an anthropologist at the University of Minnesota in Minneapolis who carried out the previous study with chimps, describes the work as "very elegant" and says it makes sense that hyenas should be so adept with numbers.

"Their livelihoods depend on defending group territories and keeping track of how many rivals

Courtesy: Nature News