Olfactory Cues Modify and Enhance Responses to Visual Cues in the Common Marmoset (Callithrix jacchus)

Diurnal primates are generally considered to have a poor sense of smell and a dearth of publications in primate olfaction has done little to correct this view. We know, however, that New World monkeys, such as the common marmoset (Callithrix jacchus), have a well-developed olfactory system and display olfaction-based social behaviour. We have far less certainty as to the role of olfaction in predator- and food- based odours in Callithrichids, and indeed, in many other primate species. We also know very little about the relative importance of multi-modal cues (such as visual and olfactory stimuli combined). If visual perception is dominant, one would expect that adding perceptual cues in other modalities would elicit no or only insignificant changes in behaviour. If, however, olfaction has a greater role to play in foraging, predator detection and anti-predator responses, experimental investigations should be able to confirm this readily. We therefore tested how a colony of captive marmosets responded to a range of predator- and food-based odours and how the presence of a specific odour was expressed in behavioural changes. We found that the predator-naive marmosets responded strongly against faecal odours of predators (withdrawal) and with considerable curiosity (attraction) to favourite food-based odours. Signs of fear and pleasure were also noted. We then combined the most unpleasant and pleasant odours with the corresponding visual stimuli to test whether the addition of olfactory cues changed behaviour in comparison with that shown for visual stimuli alone. We found that there was a reduced latency to approach a food item when its odour was detectable and that vigilance increased markedly when a predator could be smelt as well as seen. These results suggest that marmosets perceive and respond to specific olfactory information and that olfaction may be more important for a broad range of functions not previously considered.