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Grub-on-a-stick: Crafty crows use tools for nutritious snacking

Captive New Caledonian crow using stick tool to extract mealworm from hole.
[Photo Simon Walker]

For New Caledonian crows, using sticks to dislodge beetle grubs from rotting tree trunks takes a lot of time and practice, but the payoff is that the grubs are extremely nutritious, scientists report.

Tool use is so rare in the animal kingdom that its evolutionary origins have been difficult to study, so researchers have been keenly interested in the wild crows of New Caledonia, in the South Pacific, which use sticks to remove beetle larvae from their burrows.

Scientists know that this type of tool use is the main way that the birds access the larvae, that it requires considerable skill that young birds must acquire, and that it's time-consuming, even for adult birds that are adept with the tools.

Wild New Caledonian crow with beetle larva in its bill.
[Photo: Jolyon Troscianko]

Christian Rutz of the University of Oxford and his colleagues wondered why the birds go to all this trouble.

The researchers analyzed biochemical information from the feathers and blood of wild crows, to estimate how much of the crows' diet consisted of beetle grubs. They used this information to estimate how much energy these diets provided the crows.

The results show that just a few larvae can satisfy a crow's daily energy requirements, highlighting one of the advantages of learning to use tools.

This research appears in the 17 September issue of the journal Science.