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Absence of cognitive bias to flanges in orang-utans14961985), a more recent report did not find any colour bias (Sauciuc et al., 2016). It is important to note that both reports concern single-subject observations. A more comprehensive study in rhesus macaques demonstrated a bias towards red food items, but this bias did not extend to non-food objects (Skalníková et al., 2020). In conclusion, we found evidence for the notion that orang-utans have a sensory bias towards red objects, although this seems to conflict somewhat with existing literature on colour biases in primates.In addition, orang-utans were more likely to select the dot associated with flanged male stimuli if it was in the lower portion of the screen, potentially reflecting an energy conservation mechanism. Bornean orang-utans are extremely well-adapted to low fruit availability. This is reflected in their extremely low levels of energy expenditure (Pontzer et al., 2010) and their energy-efficient locomotion style (Roth et al., 2017; Thorpe et al., 2007). This inclination to conserve energy may also manifest in their behaviour during our experiment. In the preference tasks, the locations of the dots was randomized in a circular way between trials, with both dots appearing in exact opposite position equidistant from the center of the screen. While this approach helped to avoid anticipatory clicking by the orang-utans, it did result in differential energy costs associated with the dots. Clicking the dot in the upper portion of the screen required them to lift their arm further compared to clicking the dot in the lower portion of the screen. Consequently, the orang-utans were more inclined to select the dot in the lower portion of the screen. It is important to acknowledge this limitation in our experimental design. Nevertheless, even after accounting for the vertical location of the dots, we found no bias for flanged or unflanged stimuli (Supplementary Table 4). Thus, the strong urge of orang-utans to conserve as much energy as possible may influence their performance during cognitive tasks. Future studies on orang-utan cognition should consider the aforementioned effects of colour and dot location on choices. These biases underscore the need for a biocentric approach to animal cognition, which takes into account a species’ uniquely adapted perceptual system (Bräuer et al., 2020). Interestingly, however, the notion that orang-utans try to conserve energy during cognitive tasks opens up intriguing avenues for further research. If orang-utans are so prone to conserve energy, it might be possible to exploit this tendency by presenting them with an effort task. Previous studies with primates have developed effort paradigms that are relatively easy to use. These paradigms allow individuals to control the presentation of stimuli by holding a button (i.e., exerting effort). For example, Tom Roth.indd 149 08-01-2024 10:41