Abstract
Visual and olfactory cues provide important information to foragers, yet we know little about species differences in sensory reliance during food selection. In a series of experimental 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 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) produce distinct visual and olfactory cues (the latter determined chemically). We first showed that lemurs preferentially selected high-quality foods 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 sensory cues (while holding food quality constant). Among our study subjects that showed relatively strong preferences for high-quality foods, folivores required both sensory cues combined to reliably identify their preferred foods, whereas generalists could identify their preferred foods using either cue alone, and frugivores could identify their preferred foods using olfactory, but not visual, cues alone. Moreover, when only high-quality foods were available, folivores and generalists used visual rather than olfactory cues to select food, whereas frugivores used both cue types equally. Lastly, individuals in all three of the study species predominantly relied on sight when choosing between low-quality foods, but species differed in the strength of their sensory biases. Our results generally emphasize visual over olfactory reliance in foraging lemurs, but we suggest that the relative sensory reliance of animals may vary with their feeding ecology.
Highlights
As foraging is a costly behavior, animals enhance their efficiency for detecting differences in food quality via sensory adaptations [1]
Provided that the lemurs were sensitive to the items’ volatile compounds, red and green Photinia and S. lycopersicum should have been distinguishable based on olfactory cues alone
Animals rely on a suite of sensory cues to search for, identify, and acquire appropriate foods, and when food signals are multimodal, their senses can function synergistically to improve foraging efficiency [61], [62]
Summary
As foraging is a costly behavior, animals enhance their efficiency for detecting differences in food quality via sensory adaptations [1]. Animals can adjust their food selection to regulate nutrient intake [2,3,4] or to avoid plant secondary metabolites that may be harmful or difficult to digest (reviewed in [5]). Two main senses involved in food detection and selection by mammals are sight [6,7,8] and scent [9], [10]. Whereas the use of these senses during foraging is well recognized, further work is needed to elucidate the relative contribution of vision versus olfaction in enhancing the food-quality choices of multisensory animals. In a comparative study of Malagasy lemurs (Primates; Strepsirrhini), we use an experimental approach to investigate species differences in sensory reliance. We compare three diurnal species that have different feeding ecologies, including frugivory and folivory, as we expect that dietary specializations may require differential emphasis on these two senses
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