"We have watched the extended drama of baboon interactions and have a detailed understanding of the hierarchy of their relationships," Seyfarth said. "But this could be just idle anthropomorphism. The big question is whether the baboons themselves have an equally sophisticated view of their society."
Dominant baboons make threatening grunts, which lower ranked baboons answer with supplicating screams. The researchers tape-recorded the calls of known individuals, then used a computer to mix and match the grunts and screams to make it seem as if a lower-ranked baboon was effectively dominating a higher ranked baboon. Then, in a playback experiment, the researchers played recorded interactions to individual baboons to see if there would be a response. Some playbacks mimicked the existing hierarchy, whereas others mimicked a rank-reversal, either between two members of the same family or between two members of different families.
"Rank-reversals run counter to their expectations, and a baboon will momentarily pause and give a look, just as you might if you didn't quite believe what you had just heard," said Thore Bergman, lead author on the paper. "Our results demonstrated that these relationships were real and relevant to these baboons."
By analyzing video of the baboons' responses to various rank-reversals, Seyfarth, Cheney and their post-doctoral colleagues Bergman and Jacinta Beehner found that baboons respond more strongly to recordings mimicking rank-reversals between families than within families.
"Rank reversals within families are surprising, but rank-reversals between families are of potentially much greater importance and we see that the baboons recognize the significance of these events," Seyfarth said. "To do so, they must be astute observers, watching animals interact and deducing a social structure on the basis of what they've seen."
Contact: Greg Lester
University of Pennsylvania