Long-tailed macaque monkeys have a reputation for knowing how to find food — whether it be grabbing fruit from jungle trees or snatching a banana from a startled tourist.
Now, researchers say they have discovered groups of the silver-haired primates in Indonesia that fish.
Groups of long-tailed macaques were observed four times over the past eight years scooping up small fish with their hands and eating them along rivers in Indonesia's East Kalimantan and North Sumatra provinces, according to researchers from The Nature Conservancy and the Great Ape Trust.
The species had been known to eat fruit and forage for crabs and insects, but never before fish from rivers.
"It's exciting that after such a long time you see new behavior," said Erik Meijaard, one of the authors of a study on fishing macaques that appeared in last month's International Journal of Primatology. "It's an indication of how little we know about the species."
Meijaard, a senior science 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 well-known to researchers — an ability to adapt to the changing environment and shifting food sources.
"They are a survivor species which has the knowledge to cope with difficult conditions," Meijaard said Tuesday. "This behavior potentially symbolizes that ecological flexibility."
'They are very adaptive'
The other authors of the paper, which describes the fishing as "rare and isolated" 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 such details can offer insight into the "complexity of these animals."
"It was not surprising to me because they are very adaptive," he said. "If you provide them with an opportunity to get something tasty, they will do their best to get it."
Fuentes, who is not connected with the published study, said he has seen similar behavior in Bali, where he has observed long-tailed macaques in flooded paddy fields foraging for frogs and crabs. He said it affirms his belief that their ability to thrive in urban and rural environments from Indonesia to northern Thailand could offer lessons for endangered species.
"We look at so many primate species not doing well. But at the same time, these macaques are doing very well," he said. "We should learn what they do successfully in relation to other species."
What got monkeys into fishing?
Still, Fuentes and Meijaard said further research was needed to understand the full significance of the behavior. Among the lingering questions are what prompted the monkeys to go fishing and how common 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 while studying orangutans.
Wich said it wasn't until Meijaard told him about his fishing macaques that he realized he had overlooked the unique behavior altogether.
"I was astonished. I thought it was a normal observation," Wich said. "I was really surprised because it indicated to me that you keep on making these observation about primates but you only discover they are interesting when you compare them with others."
Meijaard said the fishing behavior could be prompted by food shortages, droughts resulting in lower water levels that make it easier to catch fish, or habitat destruction that eliminates a key food source.
"There have been studies on macaques from East Kalimantan in the past showing that during especially dry years they run out of food and switch to alternative food sources such as insects, leaves or even bark, which is not normally in their diet," he said.
Meijaard also said he felt the behavior was not isolated to a few macaques, noting that he observed younger monkeys watching their elders fish and then mimicking their behavior. He also said the behavior occurred in two unrelated groups.
Paul Garber, an expert on primate behavior at the University of Illinois who read the study, said there was not enough information to determine whether it was something that was part of the macaques' culture or an isolated event. But he said it warranted further study.
"What I feel is most interesting about the observations of fishing is the possibility of documenting whether and how this novel behavior is passed or transmitted through the population," he said.