Rhesus Monkeys Have Stronger Sense of Smell Than Scientists Previously Surmised, Researchers Say

Rhesus monkeys (Macaca mulatta) rely on their sense of smell to sniff out members of their social groups and to weed out those who don't belong, reveals a new study from the University of Leipzig, Germany. For a long time now, scientists have believed that old world species, such as the rhesus monkeys, possess a poor sense of smell. After their study, scientists now believe that the olfactiory senses (sense of smell) of rhesus monkeys plays a huge role in their social lives, according to the university's news release, which the monkeys use to defend their territories, to find adequate sleeping sites and to select a mate. 

Rhesus monkeys tend to live in large social groups of up to 80 individuals withing an extremely broad geographic range. In fact, living in a variety of habitats, which is one reason why they're regarded as some of the best known old world monkeys in the world. 

For their study, researchers examined rhesus monkeys living on the island of Cayo Santiago in Puerto Rico. These animals do not have distinct scent glands, nor do they exhibit scent markings typical for olfactory communication among social groups. In total, researchers collected body odor samples of 33 adult females that they kept in individual aerated containers. Later, these were presented to 74 rhesus monkeys. All of this allowed researchers to observe behavioral responses and to determine if the monkeys were able todistinguish between members of their own and other social groups by using their sense of smell.

Monkeys of both sexes tended to inspect the female odors belonging to individuals from other groups for much longer than when sniffing the scents of females from their own groups. This suggests the monkeys are able to recognize familiar smells, researchers explained in their study. 

"Our findings for the first time uncover key roles of olfactory communication in a primate species not possessing distinct scent glands and thus may help to shed light into the evolution of primate olfactory communication," Stefanie Henkel, lead researcher from the University of Leipzig, said in a statement.   

Beyond those revelations, the tests proved that these monkeys are even able to sniff out hierarchical status. Each spent more time analyzing odor samples taken from monkeys belonging to groups that were higher ranking than their own.

"However," Henkel adds, "although our results suggest that rhesus macaques are able to distinguish between in-group and out-of-group individuals based on olfactory cues alone, the recognition of conspecifics (members of the same species) might be a more multimodal process also including visual cues or a combination of olfactory and auditory signals. Further research is necessary to fully understand the underlying mechanisms of recognition processes."

The findings were recently published in the journal Behavioral Ecology and Sociobiology.

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