Studies on the foraging behaviour of New Caledonian crows

Abstract

The evolutionary origins of tool use are puzzling. To understand why it has evolved in certain species and not in others, we need to study the environment in which the use of tools is beneficial over alternative foraging modes. The New Caledonian crow is one of a few animals that routinely uses tools for extractive foraging. This thesis focuses on several aspects of the foraging behaviour of these crows. I compared the potential relative benefits of different foraging modes, and tested ecological factors that may have provided context for tool use to evolve. In an observational study of wild crows, I documented the relative calorific gain of foraging with tools and without (chapter 2), finding that tools allow access to more nutritious prey than those available through extractive bill foraging. Crows adopted a range of foraging modes, and may have varied in their degree of tool expression, though this could be a consequence of human observer presence. I investigated this potential inter-individual variation experimentally with wild-caught crows in captivity (chapter 3). Crows switched flexibly between tool and bill foraging, and diverged in their ability and inclination to use tools. Subsequently, I experimentally tested whether perceived threat level differentially affected the likelihood to forage with and without tools (chapter 4), and found some indication that crows were less likely to use tools in the presence of a proxy predator. Lastly, I investigated whether crows’ morphologies differed as a response to supposedly divergent foraging ecologies, by analysing the most extensive existing dataset consisting of trapping data from > 200 crows from three sites (chapter 5). I detected no significant inter-population morphological differences, indicating that either foraging ecologies did not significantly vary, or their morphologies did not adapt accordingly. This thesis contributes to a better understanding of the natural history of New Caledonian crows, and of the importance of tool use in their foraging behaviour.

Date of Award	27 Jun 2018
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Christian Rutz (Supervisor)