It’s certainly something to crow about. New Caledonian crows are known for their ingenious use of tools to get at hard-to-reach food. Now it turns out that their Hawaiian cousins are adept tool-users as well.
Christian Rutz at the University of St Andrews in the UK has spent 10 years studying the New Caledonian crow and wondered whether any other crow species are disposed to use tools.
So he looked for crows that have similar features to the New Caledonian crow – a straight bill and large, mobile eyes that allow it to manipulate tools, much as archaeologists use opposable thumbs as an evolutionary signature for tool use in early humans.
“The Hawaiian crow really stood out,” he says. “They look quite similar.”
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Hawaiian crows are extinct in the wild, but 109 birds still live in two captive breeding facilities in Hawaii. That meant Rutz was able to test pretty much every member of the species.
He stuffed tasty morsels into a variety of holes and crevices in a log, and gave the birds a variety of sticks to see if they would use them to dig out the food. Almost all of them did, and most extracted the food in less than a minute, faster than the researchers themselves could.
“It’s mind-blowing,” says Rutz. “They’re very good at getting the tool in the right position, and if they’re not happy with it they’ll modify it or make their own.”
Rutz also tested young birds, who had never lived with adults or seen them use tools, and found that they too quickly learned how to use the sticks to get at food – hinting that they have a genetic predisposition to such impressive behaviour.
Because both types of crows live on islands, Rutz thinks the unique ecological conditions of tropical islands are the key.
Without many predators around to make it dangerous to focus attention on a tool-using task, or birds like woodpeckers hogging the hard-to-reach food, the crows had the time and space to evolve the complex behaviour.
But that leaves another puzzle, says Alex Taylor at the University of Auckland in New Zealand, who also studies New Caledonian crows. Why don’t other birds that live under similar conditions use tools?
Both the kaka in New Zealand and the Mariana crow in Rota, for example, live in similar environments and exploit niches where tool use would be useful, but don’t use them, Taylor points out. “The mystery of why tool use is so rare in the natural world is still not resolved,” he says.
Journal reference: Nature, DOI: 10.1038/nature19103