Scientists Have Found Another Crow That Uses Tools

In 2013, Christian Rutz travelled to Hawaii, and presented two crows with a log containing several small holes. These had been baited with meat, but were too small and deep for the crows to reach with their beaks. “Within literally seconds, one of the birds came down, looked for a stick, began probing into the holes, and started extracting the food,” he says. The crow had been raised in captivity and had never done anything like this before. And yet, it was wielding the stick like a pro. “I could tell from its dexterity that it wasn’t just a fluke. It was one of those rare moments when you know you’ve made a big discovery.”

You might be thinking that scientists have long known that some crows are exceptional tool users. Let me assure you that, yes, Rutz knows about those crows. He has studied them for a decade in the Pacific island of New Caledonia where they live. He has seen them artfully use sticks to pry grubs from wood. He has seen them care for their tools and fashion new innovative implements. But as far as he knew, their prowess was unique. There are over 40 other species of crows and ravens, and none seem to use tools so readily or skillfully as the New Caledonian crow.

Surely there must be other tool-using crows, Rutz reasoned. The family is known for its intelligence. It’s just that many of them are poorly studied and live in tropical remote islands, where it’s hard to observe their behavior. And then, Rutz realised that he didn’t need to observe their behavior at all. Another way of identifying tool users had been quite literally staring him in the face.

In 2012, he and his colleagues showed that New Caledonian crows have a face for tools. Their unusually straight bills allow them to hold sticks precisely, and their large, forward-facing eyes give them the depth perception necessary to insert those sticks into wood. These features are the crow equivalents of our opposable thumbs—they form an evolutionary signature of precise tool use.

So, which other crows had similar faces? Rutz started casually scanning images and videos, and he quickly homed in on the Hawaiian crow or alalā.

The quest could easily have ended there because the Hawaiian crow went extinct in the wild. Introduced predators, vanishing forests, and emerging diseases all contrived to turn this once-common bird into a memory, and the last wild pair vanished in 2002. Fortunately, some survived in captivity, and conservationists at San Diego Zoo Global have worked tirelessly to raise and breed the animals. As of 2013, 109 crows survived in two centers in Hawaii.  

Rutz called them up. “This might sound crazy but I have a hunch that your birds might use tools,” he said. “Yeah, yeah, we’ve seen that,” they told him.

Sometimes the birds would use sticks to grab food that had fallen outside the mesh of their cages. Also, every year, the zoo staff try to weigh the birds by baiting a weighing scale with fruit—and the crows would often foil them by just raking the fruit off with a stick. Ironically, the staff figured that this was standard crow behavior because they had heard about the New Caledonian crows. Rutz, knowing differently, booked the first flight out to Hawaii.  

He worked with two of the Hawaiian crows at first. After they quickly proved their proficiency, he tested the entire captive population of 109 birds using baited logs. He found that 93 percent of the adults were “very slick tool users”. They would deftly probe the holes with sticks on their first go, and within minutes of getting access to a log. Sure, some of them had used sticks to drag objects, but they had never had to pry food from holes. And yet, they routinely picked the right stick for the job, and some even modified their tools to improve them.

Many animal species can be trained to use tools in captivity even when they don’t do so naturally. That includes the rook—the Hawaiian crow’s closest relative. It can quickly learn to probe holes with sticks (albeit clumsily), but despite decades of regular bird-watching, no one has ever seen a wild rook use a stick tool.

The same could be said of Hawaiian crows, but Rutz says, “I truly believe that in the past, these birds would have used tools in the wild.” The captive adults all did so spontaneously and exactingly. Rutz even tested seven recently hatched chicks, which had never used sticks before and had no chances to observe tool-proficient adults. Their human keepers had been briefed to never use tools in front of them.

And yet, when confronted with a weekly baited log, all the chicks picked up nearby objects and tried their luck at probing. They were clumsy, but four of them became adept over a few months. “I think the evidence is overwhelmingly in support of this being natural tool-using behavior,” Rutz says.

“The discovery of another tool-using crow species is exciting, especially the fact that the birds have a disposition to learn to use tools,” says Sabine Tebbich from the University of Vienna. The New Caledonian and Hawaiian crows are not close relatives, which suggests that their skills evolved independently. And that takes scientists closer to figuring out why tool use arises in some of birds and not others.

It’s notable that the two tool-using species both come from remote tropical islands—New Caledonia and Hawaii. These places have no native woodpeckers, so local birds have plenty of embedded grubs to extract. These islands also have few predators. “We think that matters because using tools forces you into a head-down position that’s incompatible with scanning the sky for hawks or snakes,” says Rutz. A third bird—the Galapagos finch—also uses sticks to remove food from holes, and it also lived on islands that are free of woodpeckers and low in predators. “The plot is thickening,” says Rutz. “Something is happening on these islands.”

It’s possible that the crows’ faces also mattered. Their straight bills and forward-facing eyes might have been adaptations to tool use. Then again, they might have been pre-adaptations—features that were already there in ancestral crows and made them especially suited to using sticks. Maybe that’s why these species, and not others, became tool-users.

Narcissists that we are, we humans like to associate tool use with great intelligence. But the crows tell us that tool use might be a precarious skill, which might only emerge under the right combination of ecological privilege and fortuitous physique.

It wasn’t enough to save the Hawaiian crow. “We speculate that perhaps the last wild Hawaiian crow could no longer profitably use tools because environmental conditions had changed,” says Rutz. “Maybe the insect prey they used to target were not available, or had been replaced by invasive species.”

That’s something he will bear in mind in two months time, when, after 20 years of hard work, San Diego Zoo Global will start reintroducing some of their captive-bred birds to Hawaii. At first, the birds will have access to feeding stations that will supplement their diet if they can’t forage efficiently on their own. Over time, they’ll need to fend for themselves, and perhaps they’ll need to fish insects out of logs as part of their repertoire.

“We’ll be keeping an eye on them,” says Rutz, “and we’ll try to apply our understanding of their ecology to inform their reintroduction. Whenever I’m there in the forest, I’ll try and think like a Hawaiian crow.”

Ed Yong is a staff writer at The Atlantic, where he covers science.

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