Crows, the family Corvidae, are among the most intelligent of birds; and animals of various kinds have been reported as using tools. Mostly this is just a twig to dig things out, or a leaf to scoop things up. Most animal tools, that is, don't require much more forethought than picking up a readily-available object and using it in an obvious way.

But the New Caledonian crow, Corvus moneduloides, shows planning and craft unknown in any other animal but humans and our most recent ancestors. They hunt out particular kinds of plant and work careful, repeated patterns on them, like Homo erectus shaping an Oldowan flint. And they make hooks: even chimpanzees don't use hooks.

They came into the news in 2002 with reports of two birds, Abel and Betty, in an Oxford laboratory. Here they showed inventiveness in conditions never experienced in their New Caledonian forest home: Betty discovered the properties of wire and braced one end against a support and twisted the other with her beak, in order to hook a bucket of food out of a clear plastic well. After this invention she consistently used the technique to solve the task. There are movies of this and other feats at the address below.

A bird that can master the ideas of hooks, wires, and buckets is a menace let loose in a building: a small child, after all, is more likely to try sticking its pudgy finger into an electrical socket than to rip the gaffer tape off the toddler-proof socket, rip the toddler-proof socket off the live socket, and experiment with a specially made poking tool. Betty and Abel, as far as I know, survived, with constant vigilance from the harassed experimenters.

But if, as I did, you heard this news in passing and thought these were specially trained in clever tasks, think again. Their discoveries were spontaneous and repeatable. Given a long clear tube with food at the end and a choice of different-length twigs, they didn't guess, they usually chose one that fit. And the way they use twigs back on New Caledonia, and on the smaller Maré in the nearby Loyalty Islands, is not just as a simple digger or spear, but as a fishing line. One of their food items is the grub of a longhorn beetle. Having dug their way down to where the grubs are lying in a tree, the crows irritate them with the end, the grubs grasp the intruder with their sturdy mandibles, and the crows haul them out for dinner.

In the wild they make three different kinds of hook, by seeking out particular plants with just the right rigidity in their leaf ribs or pliant twigs, and snipping away the unwanted bits. They can work on their own moulted feathers, or on found materials like cardboard, which they can strip into usable pieces.

Their most impressive tool is the stepped pandanus leaf. This leaf is an eminently tough strap, with edges covered in reverse barbs. The crows cut out a tapered tool from one side, to give themselves maximum leverage in wielding it, leaving the other side with all its hooking power. To cut diagonally across the fibres would require a Stanley knife and a steel ruler (give them time), so they snip parallel, stepped pieces off to approximate a diagonal cut. They appear to do this perfectly every time: since the discarded pieces are found in abundance, it is clear they don't waste time in practice. Juvenile crows have been seen closely observing adults using tools, so this might be social learning.

The evidence of the pandanus "flakes" also shows that they have a very strong bias to cutting with the right side of their beak. In fact, the New Caledonian crow has the strongest lateralisation of the brain of any creature apart from humans. The parallel between these two social, tool-making, right-handed animals is intringuing. The specialised left hemisphere confers our ability to do complex sequential tasks: and the planned tool-making of Corvus moneduloides is one of the most complex so far discovered.

New Scientist, 17 August 2002
Commemorated on New Caledonian stamp:

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