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Now, researchers say they have discovered groups of the silver-haired monkeys in Indonesia that drag.

Groups of long-tailed macaques were observed four times immersing the gone by eight years scooping up slender fish with their hands and eating them along rivers in East Kalimantan and North Sumatra provinces, according to researchers from The Nature Conservancy and the Great Ape Trust.

The species had been known to take food fruit and forage for crabs and insects, but never before fish from rivers.

“It’s exciting that back such a long time you attend new behavior,” said Erik Meijaard, single of the authors of a study on fishing macaques that appeared in last month’s International Journal of Primatology. “It’s each indication of how little we know about the species.”

Meijaard, a senior system of cognizance adviser at The Nature Conservancy, said it was unclear what prompted the long-tailed macaques to go fishing. But he said it showed a side of the monkeys that is fully known to researchers — some ability to adapt to the changing environment and shifting food sources.

“They are a survivor species, that has the knowledge to cope with difficult conditions,” Meijaard said Tuesday. “This behavior potentially symbolizes that ecological flexibility.”

The other authors of the paper, which describes the fishing as “rare and single” behavior, are The Nature Conservancy volunteers Anne-Marie E. Stewart, Chris H. Gordon and Philippa Schroor, and Serge Wich of the Great Ape Trust.

Some other primates have exhibited fishing behavior, Meijaard wrote, including Japanese macaques, chacma baboons, olive baboons, chimpanzees and orangutans.

Agustin Fuentes, a University of Notre Dame anthropology professor who studies long-tailed macaques, or macaca fascicularis, on the Indonesian island of Bali and in Singapore, said he was “heartened” to see the finding published because of the like kind details can offer insight into the “complexity of these animals.”

“It was not wonderful to me because they are very adaptive,” he said. “If you provide them with an chance; fit to get something tasty, they will perform their best to get it.”

Fuentes, who is not connected with the published study, said he has seen similar demeanor in Bali, in what place he has observed long-tailed macaques in flooded paddy fields foraging for the sake of frogs and crabs. He said it affirms his belief that their adroitness to thrive in urban and rustic environments from Indonesia to northern Thailand could offer lessons for endangered species.

“We apply the mind at so sundry primate species not doing well. But at the same time, these macaques are doing very in a proper manner,” he said. “We should learn that which they do successfully in relation to other species.”

Still, Fuentes and Meijaard said further research was needed to understand the full weight of the behavior. Among the lingering questions are what prompted the monkeys to go fishing and by what means low it is among the species.

Long-tailed macaques were twice observed catching fish by The Nature Conservancy researchers in 2007, and Wich spotted them doing it two times in 1998 in which case studying orangutans.