Influence of food physical properties and environmental context on manipulative behaviors highlighted by new methodological approaches in zoo-housed bonobos (Pan paniscus).

Research on manipulative abilities in nonhuman primates, in the context of hominid evolution, has mostly focused on manual/pedal postures considered as static behaviors. While these behavioral repertoires highlighted the range of manipulative abilities in many species, manipulation is a dynamic process that mostly involves successive types of grips before reaching its goal. The present study aims to investigate the use of manual/pedal postures in zoo-housed bonobos in diverse dynamic food processing by using an innovative approach: the optimal matching analysis that compares sequences (i.e., succession of grasping postures) with each other. To characterize the manipulative techniques spontaneously employed by bonobos, we performed this sequential analysis of manual/pedal postures during 766 complete feeding sequences of 17 individuals. We analyzed the effectiveness with a score defined by a partial proxy of food intake (i.e., the number of mouthfuls) linked to a handling score measuring both the diversity and changes of manual postures during each sequence. We identified four techniques, used differently depending on the physical substrate on which the individual performed food manipulation and the food physical properties. Our results showed that manipulative techniques were more complex (i.e., higher handling score) for large foods and on substrates with lower stability. But the effectiveness score was not significantly lower for these items since manipulative complexity seemed to be compensated by a greater number of mouthfuls. It appeared that the techniques employed involved a trade-off between manipulative complexity and the amount of food ingested. This study allowed us to test and validate innovative analysis methods that are applicable to diverse ethological studies involving sequential events. Our results bring new data for a better understanding of the evolution of manual abilities in primates in association with different ecological contexts and both terrestrial and arboreal substrates and suggest that social and individual influences need to be explored further.

Vertical climbing in free-ranging bonobos: An exploratory study integrating locomotor performance and substrate compliance.

OBJECTIVES: Ecological factors and body size shape animal movement and adaptation. Large primates such as bonobos excel in navigating the demanding substrates of arboreal habitats. However, current approaches lack comprehensive assessment of climbing performance in free-ranging individuals, limiting our understanding of locomotor adaptations. This study aims to explore climbing performance in free-ranging bonobos and how substrate properties affect their behavior. METHODS: We collected data on the climbing performance of habituated bonobos, Pan paniscus, in the Bolobo Territory, Democratic Republic of Congo. We analyzed 46 climbing bouts (12 ascents, 34 descents) while moving on vertical substrates of varying diameter and compliance levels. This study assessed the average speed, peak acceleration, resting postures, and transitions between climbing and other locomotor modes. RESULTS: During climbing sequences and transitions, bonobos mitigate speed variations. They also exhibit regular pauses during climbing and show higher speeds during descent in contrast to their ascent. Regarding the influence of substrate properties, bonobos exhibit higher speed when ascending on thin and slightly flexible substrates, while they appear to achieve higher speeds when descending on large and stiff substrates, by using a "fire-pole slide" submode. DISCUSSION: Bonobos demonstrate remarkable abilities for negotiating vertical substrates and substrate properties influence their performance. Our results support the idea that bonobos adopt a behavioral strategy that aligns with the notion of minimizing costs. Overall, the adoption of high velocities and the use of low-cost resting postures may reduce muscle fatigue. These aspects could represent important targets of selection to ensure ecological efficiency in bonobos.