Long-tailed Macaque (Macaca fasicularis fasicularis) - Rinca Island, Komodo National Park, Indonesia.
A pair of long tailed macaques groom each other on Rinca island in Komodo National Park of the coast of Flores in Indonesia. This monkey has the 3rd largest range of any primate species, behind only humans and rhesus macaques, it is found throughout much of southeast Asia and is actually one of a very small number of terrestrial mammals that violate the Wallace line. All my other photos I have posted of this species (so far) have been on one side of Wallace's line and this photo is from the other. Simply put (in the words of Wikipedia): Wallace's line is "a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace that separates the ecozones of Asia and Wallacea". Across its range there are 10 subspecies of this monkey, and i was sure this was a different subspecies than in Borneo as to me these monkeys looked like they had bushier fur and more of a "beard" around the face. However i was surprised to learn that it was the same subspecies as I photographed in Borneo, M. f. fascicularis.
Here we see an example of social grooming which functions as a stress reducing activity among other things in groups of primates. In this species researchers have observed that male crab-eating macaques will groom females in order to get sex. One study found that a female has a greater likelihood to engage in sexual activity with a male if he had recently groomed her. Other than sex, social grooming is used to bond and reinforce social structures, family links, and build relationships.