The ecological cultural and cognitive context of tool use in New Caledonian crows

Humans are weird animals. We communicate with a sophisticated language, we make and use tools to transform and exploit the environment, we share knowledge and information with our peers, and we build societies of astonishing complexity. Defining 'intelligence' is a contentious topic, but most would agree that humans are equipped with unsurpassed brain powers -- an observation that only too often leads to an exaggerated perception of 'human uniqueness'. But, what exactly was it that sent us on our unusual evolutionary trajectory? Was it particular ecological circumstances that facilitated one or several key adaptations, like language or tool use, and what role did these traits play in the evolution of culture? It is reasonable to assume that, ceteris paribus, the use of tools and the accumulation of knowledge would have conferred advantages to individuals or groups in other species, yet these traits, and especially their joint presence, are exceedingly rare in the animal kingdom. There are only two species for which cultural transmission of tool technology has been suggested: chimpanzees and, my study subject, the New Caledonian crow. These crows live on a remote Pacific island, where they use tools for extracting grubs from holes and crevices. They use at least three distinct tool types, including the most sophisticated animal tool design yet discovered, and they may even culturally transmit, and progressively refine, aspects of their tool technology (some tools vary in shape). Humans are masters at accumulating cultural information over generations, as evidenced by everyday items like watches or bicycles, not to mention computers or space shuttles. No single person could design and manufacture any of these objects from scratch. We build on the technological heritage of our ancestors, and research suggests it may be this capacity that made our species such an evolutionary success story. In New Caledonia, I investigate how wild crow societies are organised, how juveniles learn their skills, and how much of these birds' daily diet is obtained with tools. I also explore whether there is anything special about these birds' home island that might explain their unusual adaptations. In fact, they may provide a unique window into our own evolutionary past, permitting rare glimpses of what factors may have driven the evolution of tool use and culture in our ancestors. But studying these crows in the wild is not easy, because they are shy and live in dense forest where visibility is limited. My team has developed tiny, animal-borne video cameras that broadcast TV-quality, colour video. These cameras are mounted on a crow's tail, and peek forward through the legs to produce a crow's-eye view of the world. As we recently reported in Science, this novel technology enabled us to hitch a ride with wild crows and obtain intimate insights into their daily lives. It has already changed our understanding of this species' foraging ecology, and it will play a key role in our future work. I complement my fieldwork with controlled experiments with captive crows: (1) to probe their cognitive capabilities (Do they understand basic physical principles? Are they smarter than other animals?); (2) to examine whether they can imitate tutors (the mechanism that would support the cultural transmission of tool technology); and (3) to explore the genetic, social and environmental contributions to the production of particular tool shapes (Do wild-caught adult crows faithfully produce certain tool shapes, and what shapes do cross-fostered juveniles produce?). In the end, I hope my research will produce a much clearer picture of how 'intelligent' these birds really are, and how their unusual behaviour evolved in the first place. It has recently been suggested that Homo floresiensis could not have been a tool user because of its small brain. New Caledonian crows disprove this, and my study of this species may shed further light on our evolutionary roots.

The New Caledonian crow (NC crow; Corvus moneduloides) is endemic to a remote, tropical island in the South Pacific, where it habitually uses tools for extracting invertebrate prey from holes and crevices. NC crows are the most prolific avian tool users, and the sophistication of their tool technology rivals, and in some aspects outshines, even that observed in chimpanzees. NC crows manufacture their own tools, their tools have complex shapes, they use at least three different tool types, and they possess the ability to solve novel problems through innovation of new tool designs. Perhaps most intriguingly, one tool type (strips cut from the edges of serrated leaves) varies in shape and complexity across the island of New Caledonia; it has been suggested that the observed pattern may reflect a single technological invention that was followed by geographical spread, with progressive refinement of the original tool design. I propose a project with three major themes. THEME 1 explores the ecological relevance of tool use in wild NC crows. A suite of novel observation tools (animal-borne video cameras; stable-isotope profiling) will enable me to estimate individual-level tool-use dependence, and its ecological and social correlates. This work focuses on the adaptive significance of tool use and may help unravel this trait's evolutionary roots. THEME 2 examines the genetic, social and environmental contributions to the production of particular tool shapes with captive subjects (cross-fostering and social-learning experiments) and social-transmission dynamics in wild populations (use of vocal dialects to identify transmission modes; social-network analysis to study information flow). Finally, THEME 3 investigates whether the species' tool-use behaviour is associated with an unusual level of general intelligence ('folk physics' experiments) and/or with particular neurological adaptations (brain anatomy; interspecific cross-fostering).