New Caledonian Crows Prefer Hooked Stick Tools, Safely Store Them Underfoot or in Holes

According to a new study, New Caledonian crows (Corvus moneduloides) strongly prefer hooked stick tools made from stems of the ground tamarind (Desmanthus virgatus) over non-hooked stick tools; importantly, this preference is also reflected in subsequent tool-handling behavior, with the birds keeping hooked stick tools safe more often than non-hooked stick tools sourced from leaf litter.

New Caledonian crows live on the tropical archipelago of New Caledonia in the South Pacific.

These birds 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.

“The temporary storage and re-use of tools can significantly enhance foraging efficiency,” said Dr. Barbara Klump, a researcher at the Max Planck Institute of Animal Behavior, and colleagues.

“New Caledonian crows in one of our study populations use two types of stick tools — hooked and non-hooked — which differ in raw material, manufacture costs, and foraging performance.”

Using a large sample of wild-caught, temporarily captive New Caledonian crows, Dr. Klump and colleagues investigated experimentally whether individuals prefer one tool type over the other when given a choice and whether they take better care of their preferred tools between successive episodes of use, safely storing them underfoot or in nearby holes.

They found that the birds 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,” said Dr. James St Clair, a researcher with the Centre for Biological Diversity at the University of St Andrews.

“This suggests that they have some conception of the relative ‘value’ of different tool types.”

“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 these objects,” the authors said.

“The method has huge potential for investigating the behavior of other tool-using animals, including our closest relatives, the chimpanzees.”

A paper on the findings was published in the journal eLife.

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Barbara C. Klump et al. 2021. New Caledonian crows keep ‘valuable’ hooked tools safer than basic non-hooked tools. eLife 10: e64829; doi: 10.7554/eLife.64829