- Entering agricultural areas to eat crops puts chimps at risk of injury or death, but a growing body of research suggests that the nutritional benefits of cultivated food keep chimps coming back.
- In a recent paper, a team of researchers carefully studied the diets of chimpanzees in Bossou, Guinea, an area where their natural habitat has been partially cleared for farming.
- They found that the crops eaten by chimpanzees were better sources of basic nutrition than available wild foods.
- The research also indicated that chimpanzees’ foraging preferences are highly specific — troops in different areas preferred different crops — indicating that any mitigation efforts must be informed by the realities of both humans and non-human apes sharing a particular landscape.
Eating crops is a risky business for chimpanzees, who run the risk of injury or death if they are caught by farmers protecting their livelihoods. But new research shows that crops grown by farmers can have important nutritional benefits for chimps, which may explain their willingness to put themselves in harm’s way.
“Crops generally offer primates energetic benefits over wild foods,” says Nicola Bryson-Morrison, research fellow at the University of Kent, U.K., and lead author of a recent paper in the American Journal of Primatology about the diets of West African chimpanzees (Pan troglodytes verus) that live within landscapes adapted to suit humans.
“Crops have been selected by humans to be palatable, easily digestible and energy dense,” Bryson-Morrison says. As well as being tasty and providing more energy, they are also convenient. Popping down to the oil palm plantation makes for a guaranteed lunch, far easier than traipsing hours to find a fruiting wild fig tree.
Of course, this does not always go down well with farmers trying to make a living. Bryson-Morrison describes crop foraging as “a principle threat to human-wildlife coexistence within anthropogenic landscapes.” She suggests that to keep the peace, “it would be preferable if chimpanzees were able to meet their nutritional requirements from the surrounding environment without relying on crops.”
But there are clear payoffs for chimps who habitually eat cultivated crops that make this unlikely. They have been found to grow bigger, live longer, lose fewer offspring, begin breeding at a younger age, and be less susceptible to parasites, according to Bryson-Morrison’s review of previous literature on the subject. They also seem to be more chilled out: Chimp populations adapted to eating crops often spend less time looking for food and more time resting.
Understanding crop foraging
Bryson-Morrison’s research compares the macronutrient content (fats, proteins and carbohydrates) of wild foods and farmed foods foraged by chimpanzees in Bossou, Guinea, an area where their natural habitat has been partially cleared for farming.
When this happens, wild food options decrease and are replaced by an abundance of other foods in crop form. This sets the stage for human-wildlife conflict: humans can’t afford to lose crops they have worked hard to grow on slim profit margins. But chimpanzees and other animals still need to eat to survive.
Bryson-Morrison and her team observed what 13 chimpanzees ate during 568 hours of feeding, collecting samples of 24 wild species from the same trees, plants and food patches, and 11 crop species. Before carrying out nutritional analysis, they processed samples as they saw chimps do: removing the skins of some fruits and the tough outer layers of stems, keeping only the fruit pulp and soft inner pith they saw the chimps chewing and swallowing.
The analysis found that crops eaten by chimpanzees contain more easily digestible carbohydrates and less indigestible fiber, making them a higher-quality source of basic nutrition for primates.
Bryson-Morrison also found that chimps in Bossou regularly eat crops, such as pineapple, cassava, rice and maize, that chimp communities in other farmed areas ignore, even though the nutrient content across sites was found to be similar. This suggests chimps aren’t picking what to eat just because of macronutrient levels — something else must be at play.
Chimpanzees may eat crops for many reasons, Bryson-Morrison says: lack of alternative food sources, a need for specific nutrients, easy access to high volumes of food, or even cultural preferences learned from their troop. “Each of these scenarios require very different management strategies in order to implement effective … mitigation techniques and strategic land-use planning,” she says.
In areas where humans and wildlife need to live together, understanding nutritional drivers behind crop-foraging behavior is key to ensuring conservation measures are sustainable for both local farmers and wildlife, researchers say.
For apes and other animals, is always a trade-off between avoiding predation and getting enough food. “The fact that many crops offer primates energy benefits over wild foods means that they may be willing to take greater risks to acquire these foods,” Bryson-Morrison says. For farmers, this can be a headache as “their crop-foraging deterrent methods may not be very effective if the chimps perceive that the energetic benefits outweigh the risks,” she says.
In fact, chimps at Bossou have been observed moving through fields en masse instead of in their usual smaller foraging groups, and they do it on the down-low, making less noise than when foraging wild foods, according to Bryson-Morrison. This, she says, is an indication they find crops worth adapting their foraging strategy for, continuing despite the risk of being caught by farmers.
There is no one-size-fits all solution to conflict over crops, Bryson-Morrison says. Factors influencing crop foraging and the human response to it vary across communities and regions. As a result, mitigation efforts should take local variables into account, and the needs of people and wildlife should be considered as one, she says, advocating for “a more holistic approach to ecological sustainability at the local level.”
“Locals must have an active voice on what effective protection measures should look like,” says Susana Kosta, a researcher at the University of Coimbra, Portugal, and vice president of the Portuguese Association of Primatologists. Kosta, who was not involved in Bryson-Morrison’s research, says that people, often women and children, directly working with crops should be more involved in decision-making on how to protect them. “Their knowledge about wildlife behaviour and dietary habits need to be taken more seriously.”
Kosta says possible solutions include selecting crops that primates find less appealing, expanding plantations to produce extra crops that primates are free to eat, and doing away with compensation plans, which she says are transient.
For Bryson-Morrison, this begins with “understanding foraging decisions and nutrient acquisition within the context of human disturbances,” which she says is “vital for sound management planning that balances the needs of both people and wildlife.”
- Bryson‐Morrison, N., Beer, A., Gaspard Soumah, A., Matsuzawa, T., & Humle, T. (2020). The macronutrient composition of wild and cultivated plant foods of West African chimpanzees (Pan troglodytes verus) inhabiting an anthropogenic landscape. American Journal of Primatology, 82(3). doi:10.1002/ajp.23102
- Warren, Y., Higham, J. P., Maclarnon, A. M., & Ross, C. (2010). Crop-raiding and commensalism in olive baboons: The costs and benefits of living with humans. Primates of Gashaka, 359-384. doi:10.1007/978-1-4419-7403-7_8
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