Experimental investigations of cognitive abilities in a socially complex mammal, the spotted hyena (Crocuta crocuta)
The evolution of intelligence is a topic that has fascinated us ever since Charles Darwin first proposed that humans share many mental traits with other animals, and that the differences in cognitive abilities between humans and other animals are a matter of degree, not kind. Currently, the leading theory to explain the evolution of intelligence is the Social Intelligence Hypothesis (SIH), which posits that complex cognitive abilities evolved due to selection pressures associated with life in complex societies. This hypothesis was originally conceived to explain the evolution of intelligence in primates, and most work on this topic has focused on primates. However, if the SIH is correct, then many of the cognitive abilities observed in primates should also occur in non-primate mammals that live in primate-like societies.
In this dissertation, I test this prediction of the SIH by experimentally investigating several previously unexamined cognitive abilities of spotted hyenas (Crocuta crocuta) and then comparing the results of these studies to those from primate systems. Spotted hyenas are an ideal system for testing the SIH as they share many life history traits with cercopithicine primates including complex, stable, and hierarchical societies. Spotted hyenas and primates last shared a common ancestor 90-100 million years ago. Thus, similar cognitive abilities in these taxa could be attributed to convergent evolution and would provide important support for the SIH.
Spotted hyenas live in fission-fusion societies in which individuals travel, rest, and forage in subgroups that change frequently in size and composition. Numerical imbalances duringintergroup conflicts can be more extreme in these societies when compared to more cohesive social groups. Thus, an ability to assess numerical advantage should be highly advantageous for individuals in fission-fusion societies. I used playback experiments to test whether spotted hyenas follow predictions of game theory and assess numerical advantage when presented with calls from varying numbers of simulated intruders. As predicted, hyenas responded more cautiously when they were outnumbered and were more willing to take risks when they had the numerical advantage. Additionally, hyenas showed comparable abilities to those demonstrated in chimpanzees and African lions, both of which live in fission-fusion societies.
I then examined technical intelligence and learning in both wild and captive spotted hyenas by investigating their responses to a novel technical problem. These experiments illuminated the role of the diversity of initial exploratory behaviors, persistence and neophobia in determining innovative problem-solving success. I found that individuals who exhibited a wider range of exploratory behaviors when first confronted with the novel problem, and who approached the novel object faster, i.e., were less neophobic, were more successful in solving the problem. Hyenas showed trial-and-error learning and became significantly faster at solving the problem as they gained experience with it. Lastly, I experimentally demonstrated that spotted hyenas learn from watching conspecifics solve a novel technical problem and that they use the same, relatively simple, mechanism of social learning as vervet monkeys and macaques.
These experiments inform our understanding of the cognitive abilities of hyenas. Moreover, comparing these studies to those from primates helps us understand the selection pressures that have shaped the evolution of intelligence. Generally, these results support the SIH by providing evidence that primates and carnivores with similarly complex social systems have evolved similarly complex social, technical and numerical cognitive abilities.