Nature: Crows keep their best tools extra safe – suggesting they have a concept of relative ‘value’

New Caledonian crows are more likely to keep their most special tools safe — the ones which are more effective and took time to fashion — a study has determined.

According to University of St Andrews biologists, the findings suggest that birds can understand the relative value of different items.

The crows are renowned for using various tools, held in their beaks, to extract prey from their hidey-holes in trees and the like — but they have to put them down to eat.

This latest research builds upon the findings of an earlier study that found that crows use two methods to keep their tools safe from theft or loss when they are not being used.

You can keep them underfoot securely, hide them behind bark, and even in holes in the trees nearby.

The team found that such practices are more often employed with hooked tools — which are both more difficult to obtain and can be ten times more effective in use.

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New Caledonian crows are more likely to keep their most special tools extra safe — the ones which are more effective and took time to fashion — a study has determined. Pictured: A crow inserts an efficient hook tool in a hole on a branch.

In tests with 27 New Caledonian crows, the researchers found that the birds employ two different types of tools — complex hooked ones (right), painstakingly crafted from relatively scarce plants, and basic straight twigs and stalks (left) picked off of the ground. Christian Rutz, a University of St Andrews paper author, stated that while hooked tools can be more costly, they also work more efficiently.

The study was undertaken by biologist James St Clair of the University of St Andrews and his colleagues.

‘It was exciting to see that crows are just that bit more careful with tools that are more efficient and more costly to replace,’ Dr St Clair said.

He added that this suggests they understand the relative “value” of different types of tools. 

In tests with 27 New Caledonian crows, the researchers found that the birds employ two different types of tools — complex hooked ones, painstakingly crafted from relatively scarce plants, and basic straight twigs and stalks picked off of the ground. 

Based on observations by the team, it was found that the hooked tools are more often kept safe by the birds, either hiding or standing on them. The ‘ten-a penny’ straight tools, which were easier to replace in the event of loss or theft, were less likely to be protected.

‘Hooked tools are not only more costly to obtain, but they are also much more efficient,’ explained paper author and ecologist Christian Rutz, also of the University of St Andrews.

“Depending on what task they are performing, these tools can be used to extract prey up to tenx faster than non-hooked, standard tools.”

The crows’ behaviour, noted lead author Barbara Klump — who is now based at the  Max Planck Institute of Animal Behaviour in Radolfzell, Germany — is not that dissimilar to how us humans often treat our possessions.

The behavioural expert noted that many people will be fussy about their new phones, trying to make sure they don’t get dropped, scratched or lost.

“But we can handle an old smartphone with a cracked screen fairly carelessly.” 

The crows are renowned for using various tools, held in their beaks (as pictured), to extract prey from their hidey-holes in trees and the like — but they have to put them down to eat

The researchers claim this is the very first study to explore how tools-wielding mammals value various types of implements.

Similar analyses could be applied to other tool-bearing creatures, they added — including our closest relatives, the chimpanzees. 

Full results of the study have been published in the journal eLife.