Clever crows have long been known to use tools. But one species is particularly technologically advanced: New Caledonian crows actually make their own hook-shaped tools, which they use for foraging.
Biologists have known about the shrewd tool-use of the South Pacific island-dwelling crows for a decade, but they had seen the birds make tools only in laboratory experiments. Sure, the crows built tools in that artificial setting, scientists reasoned, but how skillful were the feathered engineers in the wild?
Despite hundreds of hours of observing New Caledonian crows in their natural habitat, scientists had only glimpsed the behavior and still had questions about how the crows did it. So two biologists in the United Kingdom devised a way to catch the resourceful birds in the act.
The duo built tiny cameras that they attached to the birds' tail feathers to capture video of the wild crows' natural foraging behaviors.
And it worked. The crows were caught on film making and using a hook-shaped tool to pull grubs, insects, larvae, and other tasty morsels from crevices in logs and from beneath leaf litter, according to a paper published Wednesday in the Royal Society's journal Biology Letters.
At first glance, the researchers couldn't tell if they'd captured the crows' behavior on film or not.
"The first time you go through the footage, it just looks like a wobbly mess because the cameras are bouncing all over the place," Jolyon Troscianko, one of the study's authors, tells The Christian Science Monitor in an interview.
But, the University of Exeter behavioral ecologist says, when they slowed the video down and looked at it frame-by-frame, they were able to spot the crow shaping a stick into a hooked tool.
A crow uses a twig with a V-shape in it to make the tool. The bird snaps the stick in two places, just above the joint where the twig branches and just below it. That joint then forms a small hook at the end of a long, handle-like stick.
To shape the tool, the bird peels bark off the stick, removes any leaves attached, and will work the end to fashion it into a sharp hook.
This process takes the crows about a minute, says Dr. Troscianko. But it's an ongoing process.
"If it's not working very well, they might nibble at the end of it to try and sharpen it," Troscianko says. So they "modify the tool as they go."
Other animals' tool use is generally simple. An animal might poke around with a stick to investigate its surroundings or smash a nut with a rock to get a snack. In those scenarios, the animal is not making its own tool, making the New Caledonian crows stand out as toolmakers.
"Tool use is fairly rare in the animal kingdom, but manufacturing tools is exceedingly rare. There are very few animals, apart from humans, that actually manufacture anything that resembles a complex tool," Troscianko says.
Chimpanzees, one of humans' closest living relatives, are one of those animals. "But even what the crows can make is, in terms of complexity, is almost on par with the chimpanzees," Troscianko says. "It just shows that you don't necessarily need a big brain to be adaptive and adept at making tools."
But other species of crow may be more bird-brained than the island-dwelling crows filmed in this study.
"They are incredibly special," Troscianko says of the New Caledonian crows. "No other crow, pretty much no other bird, manufactures tools like these."
Sure, other crows use simple tools. But, Troscianko says, "they might just be picking up a bit of rubbish and throwing it against another bit of rubbish."
Although these crows' behavior does seem to be special, they aren't alone in regularly fashioning tools for foraging. "There is one other bird that habitually uses tools and that's the Galápagos woodpecker finch," Troscianko says. "It uses cactus spines to get insects out of crevices."
Other birds have been observed using tools in other, albeit more simple, ways. In a recent study, researchers observed parrots in an aviary using pebbles and date pits to grind up shells to create calcium powder for a nutritious snack.
Complex tool use is thought to set humans apart from other animals.
"Humans are really odd in that we fashion the world around us with amazingly complex tool use," Troscianko says. Studying other animals that use tools "might help us understand how tool use might have evolved."
"It's fascinating to know more about what evolution can throw up," Troscianko says. "If nothing else, it's just fascinating to know the limits and abilities of other nonhuman animals."