Night-time activity of primates discovered
Image: Suneko
Though most primates are active either during the day or night, research involving camera traps has suggested that some monkey and chimp day dwellers are also active during the night.
Chia Tan of the San Diego Zoo Institute for Conservation Research documents her findings in the latest issue of Primates Journal. The Guizhou snub-nosed monkey, Rhinopithecus brelichi, was once thought to be exclusively diurnal but Tan says:
"Our camera trap photos showed Guizhou snub-nosed monkeys moving in trees at night. We believe the monkeys were on their way to search for food."
The Guizhou snub-nosed monkey is endangered, with a population of just 700-800 confined to Fanjingshan in Southwest China. Tan and colleagues Yeqin Yang and Kefeng Niu found that the monkeys were active day and night all year round, but were more active at night in the early spring and autumn.
Tan explained: "We think the monkeys are extending their activity beyond daylight hours to increase feeding, and the highly sought after food items are young leaves in spring and fruit and seeds in autumn.
"It makes sense that the monkeys take advantage of these super nutritious foods to maximize their reproduction and survival. Spring and autumn are critical times for the monkeys; they are the birthing and mating seasons, respectively."
It is suspected by researchers that due to the foggy conditions in their forest home, the monkeys may have evolved the ability to see in low light conditions. They appear to have overcome the dangers that could come with a combination of poor eyesight and night predators such as the clouded leopard.
Guizhou snub-nosed monkeys are not the only primates found to have night-lives, such as the aptly named owl monkey. Another recent camera trap study by Tan and colleagues has also revealed nocturnal behaviour in savanna chimpanzees in Fongoli, Senegal.
Tan's research has been described as a “novel approach to the study of primate activity” by Eduardo Fernandez-Duque, and associate professor of anthropology at the University of Pennsylvania. He adds:
"The article combines the use of some new technology with traditional approaches to learn that the snub-nosed monkeys, traditionally considered diurnal, may show some nocturnal activity under certain circumstances.”
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