Despite the importance of eye movement analysis in comparative and cognitive studies, the eye movements of great apes have not been examined until recently using the eye-tracking method. This is due to the lack of a non-invasive, unrestrained eye-tracking method, which is appropriate for great apes. In this review, I first show how a recent user-friendly corneal-reflection eye-tracking technique captures their eye movements accurately and stably. I then introduce several comparative studies that examined the eye movements of great apes (chimpanzees, gorillas, and orangutan) and humans when viewing still pictures of scenes and faces under similar conditions. The major conclusion of those studies is that, although the species were similar in their viewing patterns, quantitative species differences existed in those similarities. That is, great apes and humans viewed similar parts of scenes/faces for similar lengths of time. However, great apes and humans differed from each other in that (1) great apes scanned the scene more quickly and more widely than did humans in general, and (2) humans viewed the eye part of faces longer than did great apes. These species differences may reflect their cognitive differences. In future, there are at least three promising directions. (1) Movie presentations about other individuals' actions to reveal how great apes anticipate the others’ action goals. (2) A wearable eye-tracker to reveal how their vision actively interacts with the environment. (3) A correlational analysis to reveal how their basic gaze patterns influence their gaze-related performances such as gaze following and observational learning.

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In this review I introduce the literature concerning variations in the feeding ecology of wild Japanese macaques (Macaca fuscata), for which many Japanese primatologists have collected data for more than 60 years. Specifically, I review 1) temporal, 2) spatial, and 3) inter-individual variations in the feeding ecology of the macaques. Food resources of the macaques in habitats exhibit temporal shifts (in short-term, seasonal change, and inter-annual change), which consequently affect feeding-related behavior, such as ranging patterns, activity budgets, and degree of crop-raiding. On the other hand, temporal changes in feeding sometimes affect inter-specific relationships. Food environment differs regionally, which is attributed to forest productivity and flora, and/or physical conditions such as temperature and snowfall. The feeding ecology differs even between neighboring troops inhabiting different forest structures. A troop of macaques consists of males and females of different ages and social ranks whose nutritional demands vary. Such inter-individual variation within group affects their feeding ecology, which consequently affects population parameters through competition over food resources. Variation in food habits would affect other ecological phenomena, such as seed dispersal and plant community structure. Finally, I discuss several challenges facing future studies of the feeding ecology of Japanese macaques.

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