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.