The Forms and Structures of Chimpanzee Algae Fishing.

Variation in the expression of behavior is a critical measure for understanding how socio-ecological factors shape cognitive and behavioral evolution and adaptability. Detailed descriptions of behavioral repertoires and how they are combined and structured into programs of actions is an essential foundation for this work. However, comparisons within and across species are made challenging where there is substantial variation in the level of detail at which behaviors are described. Here, we use a systematic, multi-level framework to describe a recently reported chimpanzee tool use behavior-algae fishing-at three levels of granularity: Functional Behavioral Categories, Behaviors, and Behavioral Elements. We then describe how these units are combined into structured programs of action. Despite variation in the detail at which tool use behaviors are described in the literature, we suggest that chimpanzees' algae fishing repertoire is relatively large, as compared to other forms of chimpanzee tool using, and flexibly deployed at each level of description. The varied use of techniques by adults suggests that there is no single optimal solution for algae fishing, and that chimpanzees benefit from maintaining multiple strategies for this dynamic foraging challenge. We provide an example of a structured framework that can be applied to describe different levels of detail and used to show within- and between-task variation. Systematic frameworks that can be consistently applied across species and contexts are critical for providing the like-with-like comparisons necessary for robust investigations of species-level cognition and behavior.