A new study using motion sensitive video cameras has revealed how New Caledonian crows use tools in the wild.

Previous work has shown the sophisticated ways in which crows can use tools in the laboratory, but now a team of scientists from Oxford University and the University of Birmingham have investigated tool use in its full ecological context. The researchers recorded almost 1,800 hours of video footage for the study and published their findings in Proceedings of the Royal Society B.

In the wild, New Caledonian crows use tools for many purposes, including 'fishing out' large beetle larvae from holes in dead wood. In the new study, the team was able to show for the first time that more larvae were extracted by crows using tools than with their beaks.

They also discovered that adult crows appeared to be much more skilled at obtaining larvae than juvenile crows, suggesting that considerable learning -- possibly from copying more experienced 'larvae fishers' -- is required for crows to become competent at this task.

Aside from recording the video footage the team also collected a large sample of tools that crows had left inserted into larvae burrows. By comparing the length of the tools to the burrows, they found that, on average, longer tools are found in deeper burrows -- suggesting that wild crows, like their cousins in the laboratory, are able to match the 'right' tool to the task. The collection also showed that wild crows do not select tools randomly, from debris on the forest floor, but are more likely to choose leaf-stems than twigs, and are more likely to use tools of a certain size range.

The research team included Dr Lucas Bluff, Dr Christian Rutz, Dr Alex Weir and Professor Alex Kacelnik from Oxford University's Department of Zoology, and Jolyon Troscianko from the University of Birmingham.

The work was funded by the UK's Biotechnology and Biological Sciences Research Council (BBSRC).