MINNEAPOLIS — Orangutans swim about as well as they fly, but research on three Indonesian islands shows that these long-limbed apes nonetheless catch and eat fish.
Orangutans living in Borneo scavenge fish that wash up along the shore and scoop catfish out of small ponds for fresh meals, anthropologist Anne Russon of York University in Toronto reported on April 14 at a meeting of the American Association of Physical Anthropologists. Over two years, Russon saw several animals on these forested islands learn on their own to jab at catfish with sticks, so that the panicked prey would flop out of ponds and into a red ape’s waiting hands.
“If orangutans can do this, then early hominids could also have practiced tool-assisted fishing,” Russon said.
Although orangutans usually fished alone, Russon observed pairs of apes catching catfish on a few occasions. In one case, an orangutan cringed and pulled away as its companion extracted a fish from a pond. Russon suspects that the onlooker was learning — or at least trying to learn — how to nab aquatic snacks.
Observations of fishing by orangutans raise the likelihood that hominids ate meat, including fish, before the emergence of the Homo genus around 2.5 million years ago (SN: 9/11/10, p. 8), said anthropologist David Braun of the University of Cape Town in South Africa. Anthropologists have traditionally held that meat-eating first assumed prominence among early Homo species and fueled brain expansion.
Fish, even more than red meat, contains fatty acids essential for human brain growth. Good archaeological evidence of fish eating goes back no further than about 2 million years ago in members of the Homo genus, which includes modern humans.
Russon and her colleagues monitored daily behavior among orangutans in Borneo from 2004 to 2006. In 2007, the researchers stocked a small pond with catfish and videotaped orangutan visits to the pond over the course of one day.
Seventeen times orangutans scavenged for fish or grabbed fish out of ponds —several times from the prestocked pond — and immediately ate their prey. Apes used sticks to jab at catfish in the prestocked pond and in other ponds as well.
Fishing isn’t common among primates, but it does occur. Chimpanzees occasionally pluck fish out of ponds, Russon said. Some monkeys that swim well, including certain macaque and baboon species, also catch fish with their hands.
What’s impressive is that orangutans spend most of their time in the trees and have no aptitude for swimming, Russon said. “They sink like stones in the water.”
Orangutans’ determined fishing efforts underscore the nutritional importance of marine foods for apes in general, not just people, Russon said. Individual orangutans in Borneo may have discovered by accident that they could grab fish along the shore and in ponds. These animals then adapted sticks to the task of catching elusive pond catfish.
Ancient hominids probably did much the same, Russon said, moving from opportunistic fish gathering to deliberate fishing.
