By Dr. Becker
Most studies of primate body language and vocal communication have been conducted on chimpanzees living in captivity, which presents a very different context than chimps living in their natural habitat.
However, a recent study has revealed that wild chimps communicate with others in their social groups about at least two subjects: their favorite fruits, and the trees where these delectable fruits can be found.
According to Discovery News:
"The study is the first to find that information about tree size and available fruit amounts are included in chimp calls, in addition to assessments about food quality."1
Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany conducted the study, which was published earlier this year in the journal Animal Behaviour.2
Wild Chimpanzees Call Out the Location of Yummy Fruit
The Max Planck research team spent over 750 hours analyzing the food calls of 9 adult chimpanzees living in the Taï forest on the Ivory Coast. Chimps make food calls only when they are foraging and observing the species and size of trees and the amount of fruit on those trees.
Lead researcher Ammie Kalan told Discovery News:
"Chimpanzees definitely have a very complex communication system that includes a variety of vocalizations, but also facial expressions and gestures.
"How much it resembles human language is still a matter of debate, but at the very least, research shows that chimpanzees use vocalizations in a sophisticated manner, taking into account their social and environmental surroundings."3
Kalan's team observed that when the chimps found fruits from the Nauclea orientalis tree, they called out at a higher pitch. The smaller the Nauclea tree, the higher the pitch of the chimps' calls. Bigger trees bearing more fruit elicited calls that were lower in pitch, and other chimps in the area were more attentive to lower-pitched calls because they knew there was more fruit available.
Interestingly, the chimps eat Nauclea fruits while sitting on the ground. This indicates the primates are using the crowns of trees (the fullest part containing the branches and leaves) to gauge the size of the fruit patches below.
According to Kalan, the fruit of these trees, called Nauclea diderrichii, are "quite big and easy to ingest, and we also know that they have a high energy content, which is important for wild animals." 4
Food Calls Seem to Signal Social Sharing Among Chimps
The researchers also observed that when the chimps came upon a large Nauclea tree, as soon as they called out, their relatives would quickly arrive to join in the feast.
This is interesting for a couple of reasons, the first being that the chimps' calls apparently tell the rest of the group something very specific that causes them to take action. Secondly, it illustrates the willingness of wild chimps to share their bounty with others in their group.
"Chimpanzees are incredibly social beings," says Kalan, "and sharing food is just one way of many that individual chimpanzees can solidify relationships within their group." 5
… Or Are Food Calls Simply an Automatic Arousal Response?
David Ludden, a professor of psychology at Georgia Gwinnett College and author of The Psychology of Language: An Integrated Approach, isn't necessarily buying that the food calls of the wild chimps of Taï forest are intended to invite friends and relatives to a fruit feast.
He points out that many primate species give alarm calls to warn others in the group about a predator threat, and they also give food calls to let others know it's chowtime.
"Because these calls appear to refer to specific objects or events," says Ludden, "some researchers believe they may provide clues to the evolutionary origins of human language."6
According to Ludden, alarm and food calls "seem to defy evolutionary logic" because in the first instance, the calling chimp is likely to draw the predator's attention, and in the second instance, making food calls means having to share your stash. That's why other researchers have proposed that the chimpanzees' calls aren't intentional acts of communication, but rather "automatic arousal responses."
"In other words, the caller can't help it," says Ludden, "and the others are just taking advantage of their friend's emotional state."
However, based on the Max Planck study results, Ludden notes that:
"As evidence comes in that alarm and food calls are intentional and not automatic emotional responses, we need to rethink the evolutionary logic behind them.
"It could very well be that the long-term social advantages of sharing outweigh the short-term benefits of being selfish. You could have that cheesecake all for yourself. But if you shared it with me, you'd also gain a friend."
Chimpanzees Are Endangered
Millions of chimpanzees used to live and roam freely in Africa, but today only an estimated 170,000 to 300,000 remain, making them an endangered species.
According to some estimates, the chimp population living on the Ivory Coast has decreased by 90 percent in the last two decades, and their numbers continue to dwindle due to habitat destruction, hunting, and disease.7
According to Save the Chimps:
"The increasing human population is encroaching ever deeper into even protected areas of chimpanzee habitats, and large scale logging is now a major threat to the forest primates of Africa. Subsistence hunting of chimpanzees as a source of meat is nothing new, but there is now a thriving but unsustainable commercial market for bushmeat (the meat of wild animals), including chimpanzees.
"Increased contact with humans, both local people and eco-tourists, has also brought the threat of diseases which may be mild in humans but lethal to chimps." 8
The World Wildlife Federation (WWF) is working in Africa to help manage protected areas and shield chimps from further destruction by:9
- Protecting chimpanzees through anti-poaching and effective law enforcement
- Helping governments establish and manage national parks
- Monitoring chimpanzee populations
- Encouraging sustainable use of forest resources in park buffer zones
- Building trans-boundary collaboration to develop partnerships between neighboring countries
If you would like to get involved, WWF has a (symbolic) "adopt a chimpanzee" program to help support its conservation efforts and protect chimps from extinction.