The effects of olfactory stimulation on the behaviour of captive slender lorises (Loris lydekkerianus)

Studies on primate sense of smell are scarce, even though odours represent the main communicative channel for many nocturnal primates such as gray slender lorises (Loris lydekkerianus). Here, we investigate the influence of natural odours on communicative and social behaviours on a group of slender lorises housed at the Frankfurt Zoo. Previously collected chemical marks from unknown conspecifics, urine from a natural predator (rusty-spotted cats) and a control setup were introduced in random order to the group enclosure. We recorded chemical communication behaviours, such as marking and sniffing, social behaviours and general activities. Using generalized linear mixed-effect models, we found that the odours did not have an effect on marking, but on sniffing behaviours of the animals. Conspecific odours decreased the sniffing frequencies of the animals (especially shortly after introduction). When predator odours were introduced, sniffing increased when compared to treatments with conspecific odours, but not in comparison to control treatments. The frequency of social behaviours, feeding and self-grooming did not change in response to predator or conspecific odours. Despite some limitations to our study, the data show a trend that natural odours may trigger some interest in group-kept slender lorises, and further examination of other novel odours may be worth studying (e.g. for potential chemical enrichment in zoos).