New Caledonian crows are a fascinating tool-using species. I worked with these birds during my PhD at Birmingham University, where I investigated some of the behavioural, ecological and morphological factors that related to their tool-use behaviour.
These crows often use tools to extract wood-boring beetle larvae from deadwood, but tool-use proficiency can take years to develop in young crows. Using novel filming methods in the wild I found that the crows can vary their tool probing strategies in response to the larva’s orientation and weight, suggesting that this apparently simple tool-use task requires costly investment whilst individuals develop subtle probing strategies. This study also suggested visual feedback could be important during tool-use.
Holding a tool in the bill places awkward physical constraints on watching the tool-tip – a problem that primates don’t encounter. I found that New Caledonian crows have a unique visual field that combines with their peculiarly straight bill, enabling them to see directly down the tool into a small hole. All other corvids have curved bills – which are ideal for probing into substrates and tearing at carrion – but would project the tool down into a narrow area of their visual field so they wouldn’t be able to see what they’re doing. To my knowledge this represents the only case of morphological adaptations for tool-use outside of the human hand, and could provide a simple explanation for the scarcity of tool-use in intelligent corvids.
New Caledonian crows are easy to spot in the wild, but they never go about their tool-using while being watched. That’s why their tool-use behaviour was overlooked by the scientific community for so many years.In order to understand how tool-use evolved in New Caledonian crows we must first ascertain the ecological importance of the behaviour. Stable isotope analysis revealed how larvae and nuts make up a substantial component of their daily nutritional intake, and our previous study using motion-triggered video cameras reveals that the majority of these larvae are extracted using tools. However, observing the tool-use of elusive wild New Caledonian crows is exceedingly difficult away from feeding tables or sites of high activity, indeed we know almost nothing about the tool-use ecology of crows in the humid forests. We therefore use animal-borne cameras that grant us a unique “birds’ eye view” of their candid behaviour.I helped make a new generation of these cameras that save the video footage to an on-board memory card, then we picked up the cameras after they’d fallen off by using VHF radio telemetry.