Senses form the interface between animals and environments, and their form and function provide a window into the ecology of past and present species. However, research on the senses used during foraging (e.g. smell, vision, touch, taste) by wild terrestrial frugivores is sparse. Here, we combine 26,094 fruit foraging sequences recorded from three wild, sympatric primates (Cebus imitator, Ateles geoffroyi, Alouatta palliata) with data on within- and between-species variation in colour vision, olfaction, taste, and hand anatomy. We hypothesize that dietary and sensory specialization shape foraging behaviours. We find that frugivorous spider monkeys (Ateles geoffroyi) sniff fruits most often, that omnivorous capuchins (Cebus imitator), the species with the highest measure of manual dexterity, uses manual touch most often, and that main olfactory bulb volume is a better predictor of sniffing behaviour than nasal turbinate surface area. We also identify an interaction between colour vision phenotype and use of other senses. Controlling for species, dichromats sniff and bite fruits more often than trichromats, and trichromats use manual touch to evaluate cryptic fruits more often than dichromats. Our findings help reveal how dietary specialization and sensory variation shape foraging behaviours, and inform methods for investigating relationships between behaviour and anatomy.

We conducted short (1–10 min) continuous focal animal samples following a published protocol (Melin et al. 2018) with strict out-of-site rules, such that we only recorded behaviour when we had an unobstructed view of the focal monkey’s hands and face.  Individuals were sampled opportunistically, based on visibility, but we rotated among sex and age classes in an effort to sample evenly across these variables. We recorded fruit investigation sequences, including each manual touch, sniff, and bite event, and whether the investigated fruit was eaten or rejected. Sniffing was coded as present (yes/no) if fruits were brought close to or in contact with the nose . “Bite” as a sensory assessment was only recorded when the fruit was rejected, as mastication is a requirement of fruit consumption and we cannot tease apart feeding and assessment for consumed fruits. We classified a fruit as eaten if at least two bites were taken. We also recorded fruit species. For each feeding bout for each individual, we calculated the number of foraging sequences that included sniffing, manual touch, bites followed by rejection, and acceptance (i.e., eaten), as well as the total number of foraging sequences per feeding bout. Foraging bouts were restricted to plant species or morphotypes that all three monkey species feed from.

More details are available in these publications:

- Melin AD, Webb SE, Williamson RE, Chiou KL. 2018 Data collection in field primatology: a renewed look at measuring foraging behaviour. In Primate life histories, sex roles, and adaptability - Essays in honour of Linda M. Fedigan (eds U Kalbitzer, KM Jack), pp. 161–192. New York, NY: Springer.

- Melin AD, Fedigan LM, Hiramatsu C, Hiwatashi T, Parr N, Kawamura S. 2009 Fig foraging by dichromatic and trichromatic Cebus capucinus in a tropical dry forest. Int. J. Primatol. 30, 753. (doi:10.1007/s10764-009-9383-9)

- Hiramatsu C, Melin AD, Aureli F, Schaffner CM, Vorobyev M, Kawamura S. 2009 Interplay of olfaction and vision in fruit foraging of spider monkeys. Anim. Behav. 77, 1421–1426. (doi:10.1016/j.anbehav.2009.02.012)

- Sánchez‐Solano KG, Morales‐Mávil JÉ, Laska M, Melin A, Hernández‐Salazar LT. 2020 Visual detection and fruit selection by the mantled howler monkey (Alouatta palliata). Am. J. Primatol. 82, e23186. (doi:10.1002/ajp.23186)

- Sánchez-Solano KG, Reynoso-Cruz JE, Guevara R, Morales-Mávil JE, Laska M, Hernández-Salazar LT. 2022 Non-visual senses in fruit selection by the mantled howler monkey (Alouatta palliata). Primates (doi:10.1007/s10329-022-00984-4)