Scientific Method / Science & Exploration

New videos prove crows can make complex tools that only humans have made before

Tiny cameras attached to the birds' tails give a clear view of corvid intelligence.

Enlarge / New Caledonian crow uses a tool to grab insects deep inside a piece of wood.

Though we've long known that crows use tools to get food (and occasionally to amuse themselves), scientists have lacked definitive evidence. Which is why two intrepid researchers invented the crow tailcam, to record the inventiveness of these birds in the wild.

UK researchers Jolyon Troscianko and Christian Metz had observed crows making tools in the wild, as had some of their colleagues. But none of them ever caught this amazing feat of intelligence on video. A couple of years ago, Metz co-authored a paper about how crows make hooked tools, carefully fashioning them out of branches, in order to get at hard-to-reach grubs inside a piece of wood. But he was quick to point out that those feats of tool-making were done in captivity—where animals often develop a penchant for tool-making that they wouldn't have in the wild. In a paper out last week from Biology Letters, however, Troscianko and Metz describe how they finally caught wild crows making their hooked tools on video.

Not to put too fine a point on it, they put cameras on the crows' butts. More precisely, they used biodegradable rubber to attach tiny cameras to the birds' two strongest tail feathers, giving the researchers a below-the-belly view of the crow's activities. Because crows often lower their heads to foot level to eat and make tools, this was also an excellent vantage point to capture tool-making in action.

Video of crows foraging, tool-making, and socializing, taken via cameras that the researchers attached to the birds' tail feathers.

To preserve batteries, the cameras only took footage for minutes at a time over the course of roughly a week. After that, the rubber attachments degraded enough that the cameras fell off the birds, and the scientists retrieved the devices from the forest floor. In these videos, above and below, you can see the range of activity that they captured. We can see the birds feeding just using their beaks, interacting with baby crows, and using tools. What's especially remarkable is that we now have solid evidence that crows make hooked tools. Humans are the only other animal on Earth to make these kinds of tools, which require several steps of preparation before they can be used. The crow must find a branch of the right dimensions, trim leaves and bark from it, and shape the hook itself. Only then can the bird insert the hook into rotted wood, snaring larvae and insects for a delicious meal. Crows also appear to use the hooks to muck around in the leaves on the forest floor, hoping to uncover more bugs.

Elsewhere, researchers have described crows making barbed tools that are carefully crafted by stripping the edges off large, serrated leaves.

More video of crows using the tailcam, analyzed by the researchers for their paper.

Troscianko and Metz estimate that the birds they observed used tools for foraging about 19 percent of the time. Generally the crows alternated between using their beaks and using tools. They filmed only among a group of crows that inhabit the island of New Caledonia. This frequently studied group is known for its sophisticated tool use, which appears to be a skill that is handed down within the birds' social groups. That New Caledonian crows use tools differently from other crow groups is a tantalizing hint that perhaps crows, like humans, may possess something like cultural groups with different social practices.

Scientists who study animal tool use have suggested that the practice arises in response to environment rather than something innate. Animals tend to use whatever is available around them to make their tools, which is why New Caledonian crows living in a forest full of diverse plants may have more tools than crows elsewhere. Relatedly, environmental explanations also make it obvious why dolphins use other sea creatures as tools, since there are almost no sticks floating around underwater. In other words, animals make do with what they have when it comes to innovation. It's possible that tool use evolved because it eased resource conflicts between species: the tool-users could eat things that other animals couldn't, thus allowing multiple species to thrive in the same place sustainably.

Regardless of how their tool use evolved, New Caledonian crows have proven themselves to be among the most adept tool-makers on the planet. When it comes to intelligence, opposable thumbs are not required.

Biology Letters, 2015.  DOI:  (About DOIs).

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