New Caledonian Crows are renowned for using different types of tools for extracting prey from tree holes and other hiding places. While they firmly hold their tools in the bill during foraging, they need to put them down to eat. This is when crows are at risk of losing their tools by accidentally dropping them or having them stolen by other crows.
Past research found that the crows, which are found only their namesake island in the Pacific Ocean, keep their tools safe when not needed. They either securely hold them trapped underfoot or they temporarily insert them into a nearby hole or behind bark. But are crows more careful when handling particularly valuable tools?
A new study says yes.
Researchers from the University of St. Andrews and the Max Planck Institute of Animal Behavior in Konstanz, Germany, have been studying the birds for years. Crows at one of the team’s long-term study sites use two different kinds of stick tools: complex hooked tools and basic non-hooked tools. Hooked tools are painstakingly crafted from a relatively scarce plant species, while non-hooked tools are simply twigs and leaf petioles sourced from the forest floor.
“Hooked tools are not only more costly to obtain, but they are also much more efficient,” explained team leader Christian Rutz. “Depending on the foraging task, crows can extract prey with these tools up to ten times faster than with bog-standard non-hooked tools.”
In a study published in December 2021 in the journal eLife, the researchers report that New Caledonian Crows are more likely to keep valuable hooked tools safe between uses than the more basic non-hooked tools. “It was exciting to see that crows are just that bit more careful with tools that are more efficient and more costly to replace. This suggests that they have some conception of the relative ‘value’ of different tool types,” noted study co-author James St. Clair.
This is the first study to investigate how animals handle and store tools of different kinds, providing an innovative way to measure how much they value the objects.
A version of this article will be published in “Birding Briefs” in the March/April 2022 issue of BirdWatching magazine.