# Feeding in Forest Chimpanzees: Do Food Type and Canopy Location Predict Positional Behavior?

## TL;DR

Chimpanzees show different feeding postures depending on food type and canopy location, suggesting diverse evolutionary paths for great ape behavior.

## Contribution

The study reveals that food type and canopy location interact to influence positional versatility in chimpanzees.

## Key findings

- Chimpanzees use more versatile postures when eating leaves compared to ripe fruit.
- In the terminal canopy, eating fruit is most associated with increased positional versatility.
- Versatility is higher in small trees and on small branches and decreases with age.

## Abstract

Distinctive aspects of great ape anatomy and positional behavior, including upright torso stability and suspension, are hypothesized to have evolved to facilitate ripe fruit‐eating in the terminal zone of tree canopies at large body size. Fossil discoveries challenge this view, and we test this perspective by investigating relationships among feeding posture, food type, and canopy zone in chimpanzees.

Focal follow data were collected over 10 months on 103 chimpanzees from Ngogo, Kibale Forest, Uganda. Generalized Linear Mixed Modeling was used to examine the effects of food, canopy location, and age on arboreal feeding posture versatility. Branch size and number, and tree size and species were also examined.

When considering all trees, consuming young leaves versus ripe fruit positively affected versatility. When examining only large‐canopy trees, eating leaves versus ripe fruit had no effect, but unripe versus ripe fruit had a negative effect. Terminal zone feeding was associated with an increase in versatility, and in this zone, consuming leaves versus ripe fruit had a negative effect. Versatility was inversely correlated with age, varied across tree species, and was higher on small branches and in small trees.

A positive “terminal zone effect” on versatility was detected in large trees, with behavioral impact varying by food type. Within the forest as a whole, consuming leaves over ripe fruit increased versatility. Thus, food type and availability may, in different combinations, lead to equifinality in great ape positional versatility. Hominoid morphofunctional specializations could thus evolve in many ecological contexts.

Ngogo chimpanzees are most suspensory when eating leaves.But while in the terminal canopy, positional behavioral versatility is higher when eating fruit.Great ape behavioral specializations may have evolved via multiple ecological paths.

Ngogo chimpanzees are most suspensory when eating leaves.

But while in the terminal canopy, positional behavioral versatility is higher when eating fruit.

Great ape behavioral specializations may have evolved via multiple ecological paths.

Ngogo chimpanzees from Kibale National Park, Uganda use versatile postures, like suspension, more when eating leaves than other foods. However, in the terminal canopy, eating fruit is most associated with versatility. Food type and availability, in different combinations, produce similar behaviors. Hominoid morphofunctional specializations could thus evolve in diverse ecologies.