Mild movement sequence repetition in five primate species and evidence for a taxonomic divide in cognitive mechanisms.

When animals forage, they face complex multi-destination routing problems. Traplining behaviour-the repeated use of the same route-can be used to study how spatial memory might evolve to cope with complex routing problems in ecologically distinct taxa. We analyzed experimental data from multi-destination foraging arrays for five species, two cercopithecine monkeys (vervets, Chlorocebus pygerythrus, and Japanese macaques, Macaca fuscata) and three strepsirrhines (fat-tailed dwarf lemurs, Cheirogaleus medius, grey mouse lemurs, Microcebus murinus, and aye-ayes, Daubentonia madagascariensis). These species all developed relatively efficient route formations within the arrays but appeared to rely on variable cognitive mechanisms. We found a strong reliance on heuristics in cercopithecoid species, with initial routes that began near optimal and did not improve with experience. In strepsirrhines, we found greater support for reinforcement learning of location-based decisions, such that routes improved with experience. Further, we found evidence of repeated sequences of site visitation in all species, supporting previous suggestions that primates form traplines. However, the recursive use of routes was weak, differing from the strategies seen in well-known traplining animals. Differences between strepsirrhine and cercopithecine strategies may be the result of either ecological or phylogenetic trends, and we discuss future possibilities for disentangling the two.