Comparing the sniffing behavior of great apes

Abstract

The importance of smell in humans is well established but we know little about it in regard to our closest relatives, the great apes, as systematic studies on their olfactory behavior are still lacking. Olfaction has long been considered to be of lesser importance in hominids given their relatively smaller olfactory bulbs, fewer functional olfactory receptor genes than other species and absence of a functional vomeronasal organ. Therefore, the aim of this study was to evaluate the use of olfaction in hominids. In particular, we observed sniffing behavior in captive groups of four species (Sumatran orangutans, Pongo abelii; Western lowland gorillas, Gorilla gorilla gorilla; Western chimpanzees, Pan troglodytes verus; bonobos, Pan paniscus) and evaluated in which contexts sniffing was used. Our results show that all investigated species frequently used the sense of smell, and that the sniffing frequency varied with species, sex, age, and context. Most sniffing events were observed in gorillas in comparison to the three other species. Sniffing frequencies were also influenced by sex, with males sniffing slightly more often than females. Furthermore, our results revealed an effect of age, with younger individuals sniffing more often than older individuals. All species mainly sniffed in the non-social context (i.e., toward food and other environmental items) rather than in the social context (i.e., at conspecifics), suggesting that the evaluation of the environment and the nutritional value of food items is of major importance to all great ape species investigated here. In contrast to the other species and female chimpanzees, however, male chimpanzees most often used olfaction to inspect their conspecifics. Together, our study suggests that olfaction is likely to be more important in great apes than previously appreciated.

Comparative chemical analysis of body odor in great apes

“…Future studies should, therefore, evaluate the effect of dominance on body odor variance in great apes, as demonstrated in mandrills where male but not female ranks could be differentiated comparing chemical profiles of scent‐gland secretions (Setchell et al, ). Overall, when comparing these results to our previous study investigating the sniffing frequency of mostly the same great ape individuals in the same setup as here (Jänig et al, ), both chemical complexity and sniffing frequency were highest in gorillas, lowest in bonobos and intermediate in chimpanzees and orangutans. Thus, both sniffing frequency and body odor complexity might resemble the general importance of olfaction for the respective species.…”

“…Gorillas ( Gorilla gorilla gorilla ) produce an individual body odor which could be distinguished by human raters (Hepper & Wells, ), and they use the strength of their body odor as a flexible tool in interunit communication (Klailova & Lee, ). Furthermore, sniffing behavior of four species of great apes was influenced by species, sex, and age (Jänig, Weiß, & Widdig, ).…”

Interdisciplinary challenges for elucidating human olfactory attractiveness

“…Other motor behaviours appear to be relevant, such as odour sampling behaviours, measured indirectly, e.g., by recording the frequency with which someone brings his/her own hand near the face after hand-shaking [53], or directly, e.g., by recording airflow variations in the nostrils (sniffing behaviour [125]). The latter, however, has never been used to our knowledge in the context of social communication in humans (but see [126] for non-human hominids). Ideally, behaviours displayed in real social interactions (e.g., speed dating experiment, see [122]) and indicating attraction or repulsion towards someone would be very informative.…”

“…by recording airflow variations in the nostrils (sniffing behaviour [135]). The latter, however, has never been used to our knowledge in the context of social communication in humans (but see [136] for nonhuman hominids). Ideally, behaviours displayed in real social interactions (e.g.…”

Group and kin recognition via olfactory cues in chimpanzees (Pan troglodytes)

“…Given the importance of olfaction in other primates including humans, the scarcity of research on the sense of smell in non-human great apes (hereafter apes) is surprising and leaves an important gap in our understanding of primate chemical communication. Although observations suggest that they use their sense of smell in various contexts [36], can discriminate between natural odours [37] and detect contaminants [38,39], no experimental investigations yet exist examining which social information apes perceive via odours. Human rater studies suggest, however, that gorillas (Gorilla gorilla gorilla) produce individually identifiable body odours [40] and that wild gorilla silverbacks use body odour as a flexible, context-dependent signalling mechanism to group members and outgroup conspecifics [41].…”