Ocular displays in macaques (Macaca), part 1: semets (small-scale patterns of conspicuous colouration about the eyes) in the southern pig-tailed macaque (Macaca nemestrina)

@paradoxornithidae @tonyrebelo @jeremygilmore @beartracker @matthewinabinett

Also see https://www.inaturalist.org/posts/54893-ocular-displays-and-what-we-should-call-them-part-2#

Macaca nemestrina (https://en.wikipedia.org/wiki/Southern_pig-tailed_macaque) differs from other cercopithecid monkeys in having eyes with conspicuous colouration.

Furthermore, the pattern of colouration varies greatly within this species, based on age and sex.

In females (https://www.gettyimages.dk/detail/photo/female-southern-pig-tailed-macaque-royalty-free-image/572636219?adppopup=true) and juveniles, the eye is somewhat similar to that in Homo sapiens (https://www.shutterstock.com/video/clip-1018659601-southern-pig-tailed-macaque-macaca-nemestrina-portrait).

The sclera (https://en.wikipedia.org/wiki/Sclera) is unpigmented, and is exposed by the wide configuration of the eyelids (albeit not as wide as in the human species).

Please see https://www.simiansociety.org/nonhuman-primate-species/pigtail-macaque/.

This 'white' sclera is most conspicuous when the animal glances sideways (https://www.istockphoto.com/photo/sad-macaque-macaca-nemestrina-gm508666008-85394433?searchscope=image%2Cfilm and https://www.facebook.com/photo/?fbid=822538356577658&set=pb.100064645033286.-2207520000 and https://www.istockphoto.com/photo/portrait-of-southern-pig-tailed-macaque-macaca-nemestrina-resting-on-a-tree-trunk-gm1418048240-464891924?searchscope=image%2Cfilm and https://www.gettyimages.dk/detail/photo/macaque-wisdom-royalty-free-image/535506761?adppopup=true).

In mature males (https://www.istockphoto.com/photo/male-southern-pig-tailed-macaque-a-medium-sized-old-world-monkey-is-in-natural-gm1016032602-273380979?searchscope=image%2Cfilm and https://www.istockphoto.com/photo/adult-southern-pig-tailed-macaque-or-sunda-pig-tailed-macaque-gm1303623601-395019844?searchscope=image%2Cfilm), a different kind of colouration becomes conspicuous, as follows:

the sclera is downplayed, and
what is instead subject to dark/pale contrast is the iris vs the inner upper eyelid - which is the palest part of the face (https://www.projectnoah.org/spottings/8055423).

The ocular (https://www.merriam-webster.com/dictionary/ocular) colouration in females and juveniles seems to communicate attention and intention, somewhat as in the human species. That in adult males seems instead simply to emphasise the stare, which is fundamentally antagonistic.

At least in part, the eyes of M. nemestrina are among the most human-like among higher primates (https://www.istockphoto.com/photo/male-pig-tailed-macaque-macaca-nemestrina-eating-an-ananas-fruit-gm2143603643-568707765?searchscope=image%2Cfilm and https://www.istockphoto.com/photo/male-pig-tailed-macaque-macaca-nemestrina-eating-an-ananas-fruit-gm2143602589-568707718?searchscope=image%2Cfilm).

Adult females:

https://www.shutterstock.com/image-photo/selected-focus-wild-southern-pigtailed-macaque-1673317477

https://www.shutterstock.com/image-photo/southern-pigtailed-macaque-macaca-nemestrina-portrait-2494296595

https://www.shutterstock.com/image-photo/mother-child-southern-pigtailed-macaque-macaca-1118599595

https://www.shutterstock.com/image-photo/southern-pigtailed-macaque-macaca-nemestrina-known-2163532001

https://www.mediastorehouse.com.au/danita-delimont/malaysia-borneo-sepilok-close-southern-13923309.html

https://www.istockphoto.com/photo/monkey-or-wild-southern-pig-tailed-macaque-gm1299267689-391941426?searchscope=image%2Cfilm

https://www.istockphoto.com/photo/monkey-or-wild-southern-pig-tailed-macaque-gm1299269413-391941448?searchscope=image%2Cfilm

Infants and juveniles:

https://www.istockphoto.com/photo/pig-tailed-macaque-gm462388163-31876366?searchscope=image%2Cfilm

https://www.shutterstock.com/image-photo/juvenile-pigtailed-macaque-macaca-nemestrina-isolated-364021712