Scientists studying New Caledonian crows, which fashion sticks into poking instruments to snag wood-boring larvae, have for the first time captured the birds’ tool use on video — thanks to a little help from the crows.
Two species are known to use hook-shape tools: humans and New Caledonian crows. For the first time, the humans have caught the birds using them on camera.
The camera crew? The crows.
There are crows all over the world, but the species on New Caledonia, a forested island in the South Pacific, is renowned for its ability to make and use tools. Among other things, the crows fashion sticks into sharp poking instruments and use them to “fish” for wood-boring larvae hiding in dead wood or tree trunks.
In a new study, scientists describe how they captured some of the crows’ most complex handiwork on video, thanks to special miniature cameras and 19 avian auteurs.
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“We’d seen it before and other researchers had seen it, but nobody had managed to shoot any videos,” said Christian Rutz, a behavioral ecologist at the University of St. Andrews in Scotland and co-author of the study, published last week in Biology Letters.
Rutz, then at Oxford, and Jolyon Troscianko, then a graduate student at the University of Birmingham in England, created “mini spy cams” specially fitted for birds. In late 2009, the researchers put them on 19 wild New Caledonian crows in hopes of documenting the birds’ unusual behavior with hooked stick tools.
“Some people think you need a large brain to use tools. These crows disprove that,” Rutz said. “They show incredibly complex tool behavior. The big question is: Why and how? What is special about the crows on this island?”
Other bird species are known to use tools. For instance, the Galápagos woodpecker finch uses cactus spines and twigs to hunt for insects, and the Egyptian vulture bangs stones against ostrich eggs to crack them open.
But the New Caledonian crow fashions its tools into a hook shape, which is unheard of for any nonhuman species. This gives the crows access to food sources that are hard to reach by using only their beaks.
Difficult island terrain makes it hard for researchers to watch the birds directly. Researchers who have tried have run into problems.
The crows “are so curious as a species that they would start observing us instead of the other way around,” Rutz said. “The bird would approach us and observe our cameras and binoculars.”
Instead, the scientists decided they needed a way to see through the eyes of a crow.
First, they built a camera that could attach to the underside of the birds’ tail feathers. These early crow cams transmitted live video back to a field worker.
But they kept losing reception.
Rutz and Troscianko thought they could get around this by recording onto micro-SD cards inside the cameras. But that meant they’d have to retrieve the cameras after they let wild birds fly away with them.
So they devised a decidedly low-tech solution: They used pieces of cheap birthday-party balloons to attach the cameras to the birds’ tail feathers. After about a week, sunlight would degrade the rubber enough for the balloon to break and the camera to fall to earth.
After that, Rutz and Troscianko used embedded radio transmitters in attempts to track the cameras and pick them up.
“Once you have a stationary signal for quite a while … chances are you either have a sleeping crow or the (camera) has fallen off,” Rutz said.
Altogether, the two were able to retrieve 10 of the 19 cameras.
Most important, four of the crows filmed themselves using tools. Those four birds spent 19 percent of their foraging time using their tools. (The rest of the time, they used their beaks.)
That only four of the 10 crows were seen using tools raises some tricky questions.
Were cameras not recording when the other birds were using tools? Or is it a sign that some New Caledonian crows don’t use tools at all?
Either way, Rutz hopes his videos can provide some insight into bigger questions about how tool use evolved and why it’s so rare in nature.
“That seems to be an evolutionary puzzle,” he said. “Why do so few animals use tools, and why are we humans so good at it?”