Once thought to be omnivores of plants and insects, new research show Japanese monkeys are hunting and eating fish

Japanese macaques who live in the Japanese Alps endure some of the world’s coldest and harshest environments during winter when food scarcity puts them at risk each year for survival.

But a new paper has discovered for the first time that Japanese macques, which typically eat bamboo leaves and the bark of woody plants and the occasional insect in winter, also hunt and eat fish.

That’s right, macaques are pescatarians!

Scientists were suspicious after studying the feces of Japanese macaques collected in the winter and DNA metabarcoding analysis revealed conclusively for the first time consumption of riverine benthos and brown trout.

Using infrared sensor cameras, researchers have now find proof that macaques are hunting. It’s an indication that foraging behavior traits have evolved to secure valuable animal protein for winter survival when food resources are scarce.

While other non-human primates, like the brown bear, can survive the harsh winter season by seasonal migration and/or hibernation, primates aren’t known to hibernate.

Japanese macaques in Kamikochi are known to remain in the subalpine zone during the winter10,14. The winter is typically a bottleneck for food availability potentially resulting in marked energy deficits, and mortality may result from famine2,8.

Japanese macaques are omnivorous, and in addition to plant food resources, such as fruits from spring to autumn, they are known to consume animal proteins, such as terrestrial insects.

However, it is difficult to obtain such animal protein resources in Kamikochi within the subalpine zone under snow cover. Regarding the behavior of Japanese macaques in Kamikochi during the winter, more than 70% of foraging has targeted the bark of woody plants and bamboo leaves protruding from the snow.

Initially, researchers thought the feces showing fish consumption was an accidental event, such as a dead fish found by chance or a dying fish caught in a small stream. They didn’t know until it was caught on camera that macaques were actively searching for the fish.

In the study, scientists observed the behavior of at least three of the four troops of Japanese macaques that inhabit the Kamikochi area. T

The behavior of the Japanese macaques along the river was observed during daylight between 19th January and 30th January 2022, and included typically the consumption of water plants and aquatic insects every day.

Regarding foraging for aquatic insects, the Japanese macaques visually found them by turning over rocks and then grabbing stonefly or mayfly nymphs on the rocks with their fingers. Also, the primates were observed looking for for drifting large stonefly nymphs and subsequently catching and eating them when the Japanese macaques turned over rocks.

In addition to these successful fishing behaviors, the primates were also observed reacting to the sound of fish splashing in the water.

Japanese macaques looked for fish by turning over rocks, and then chased the fish in shallow water. After that, when the fish escaped into a gap between the rocks, the Japanese macaque held the fish down in the stream with both hands and caught the fish with its mouth. In one small stream of groundwater origin, Japanese macaques started looking for fish by standing upright on two feet, then grasped the fish with both hands, and finally bit the fish with their mouths.

It’s likely that the behaviour of catching fish occurred accidentally, according to the researchers. The macaques first began by foraging for insects and then started catching fish.

The fish catching behaviour shown by Japanese macaques in Kamikochi may be a result of the evolution of novel foraging behaviour traits that allowed them to obtain valuable animal proteins for winter survival when food resources were scarce

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