Caledonian crows have, for the first time, been caught on video camera using hook-shaped tools to extract insects from wood. While scientists have long known that these crows were capable of using tools, not much was known about how they make and use them.
In order to study the behaviour of the Caledonian crows, small cameras were attached to the tail feathers of several crows. The cameras captured the activities of the crows over a 2-week period before falling off to be collected.
The cameras captured tool use in four of the crows used in the study. The videos captured both the foraging activity and the tool making of the Caledonian Crows. According to the study, most of the tool use occurred in trees. The tools were used to to extract mainly insect larva from crevices in wood. However, there was one instance of a crow using a hooked tool to probe for food through fallen leaves.
The making of the hooked tools was also captured on video. The crows seen fashioning hook-shaped tools used their beaks to make cuts in small twigs above and below a branching point. They then striped the bark and leaves from the twig. This process of tool crafting was seen in two crows and took only a minute for the first and three minutes for the second.
In total, tool making and use accounted for about a fifth of total forage time in the crows observed, which the researchers defined as time searching for food.
Most foraging by Caledonian crows is done without the use of tools of which the cameras captured a for a few hours. Crows were frequently seen searching through holes in tree branches in search of insects. In total, foraging accounted for about a quarter of total crow activity.
Several other animals such as primates and other birds have been observed using tools, but the Caledonian crow is one of the few that creates its own.
“They are incredibly special,” said Jolyon Troscianko, one of the authors of the study. “No other crow, pretty much no other bird, manufactures tools like these.
This study marks the first time both the action of creating and using these hook-shaped tools has been directly observed. A video showing both the use and crafting of the hook-shaped tools was released with the study and can be seen below. Several instances of crows using their tools to probe through trees can be seen. The making of sticks is also shown.
Video Credit: Jolyon Troscianko & Christian Rutz