Visual and olfactory cues provide important information to foraging animals, yet we know little about species differences in sensory reliance during food selection. In a series of experimental and observational foraging studies, we examined the relative reliance on vision versus olfaction in three diurnal, primate species with diverse feeding ecologies, including folivorous Coquerel’s sifakas (Propithecus verreauxi coquereli), frugivorous ruffed lemurs (Varecia variegata spp), and generalist ring-tailed lemurs (Lemur catta). We used animals with known color-vision status and foods for which different maturation stages (and hence quality) are marked by distinct visual and olfactory cues (the latter determined chemically). We first showed that lemurs preferentially selected high- over low-quality foods when visual and olfactory cues were simultaneously available for both food types. Next, using a novel apparatus in a series of discrimination trials, we either manipulated food quality (while holding sensory cues constant) or manipulated the sensory cues available (while holding food quality constant).
Whereas folivores required both senses combined to reliably identify their preferred foods, generalists could use either sense alone and frugivores relied more heavily on olfaction. Moreover, when selecting foods of any quality, folivores and generalists relied significantly more on vision than olfaction whereas, when selecting high-quality foods, frugivores relied equally on both senses. Lastly, we validated the consistency of our findings in a more natural setting by observing foraging behavior under semi-free-ranging conditions. Our results generally emphasize visual over olfactory reliance in foraging lemurs, but show that the relative sensory reliance varies with feeding ecology.