Wild Tibetan Macaques Use a Route-Based Mental Map to Navigate in Large-Scale Space.

Many animals face significant challenges in locating and acquiring resources that are unevenly distributed in space and time. In the case of nonhuman primates, it remains unclear how individuals remember goal locations and whether they navigate using a route-based or a coordinate-based mental representation when moving between out-of-sight feeding and resting sites (i.e., large-scale space). Here, we examine spatial memory and mental map formation in wild Tibetan macaques (Macaca thibetana) inhabiting a mountainous, forested ecosystem characterized by steep terrain that limits direct vision to 25 meters. We used an instantaneous scan sampling technique at 10-min intervals to record the behavior and location of macaques on Mt. Huangshan, Anhui Province, China, from September 2020 to August 2023. Over 214 days, we obtained 7180 GPS points of the macaques' locations. Our study revealed that the macaques reused 1264 route segments (average length 204.26 m) at least four times each. The number of feeding and resting sites around the habitual route segment, terrain roughness, and dense vegetation areas significantly influenced the use of route segments by our study group. In addition, we found evidence that the monkeys reused 48 nodes to reorient their travel path. We found that monkeys approached a revisited foraging or resting site from the same limited set of directions, which is inconsistent with a coordinate-based spatial representation. In addition, the direction in which the macaques left a feeding or resting site was significantly different from the straight-line direction required to reach their next feeding or resting site, suggesting that the macaques frequently reoriented their direction of travel to reach their goal. Finally, on average, macaques traveled 24% (CI = 1.24) farther than the straight-line distance to reach revisited feeding and resting sites. From our robust data set, we conclude that Tibetan macaques navigate large spaces using a route-based mental representation that appears to help them locate food resources in dense, rugged montane forests and heterogeneous habitats.