Smarter than the average crow, or just equipped with a face for fishing?

By Ed Yong | October 9, 2012 11:00 am

Our intelligence clearly surpasses those of our primate relatives, even though other apes and monkeys also rank within the highest tiers of animal smarts. Likewise, the corvids – the group of birds that includes crows, ravens, rooks, magpies and jays – have very sophisticated brains for birds, but one species reputedly outclasses the rest. It’s the New Caledonian crow.

Found in a Pacific island, this crow wields tools in a way that none of its relatives can match. It uses sticks to “fish” for grubs buried in dead wood, and can chosen the right tool for different jobs, combine tools together, and improvise from unusual materials. These abilities have fuelled the New Caledonian crow’s reputation as the top of the corvid class – an unusually intelligent member of an already intelligent family.

But what if it just has the right face?

If I wanted to fish for a grub, I can use my dextrous hands while moving my face around so I can see what I’m doing. The crow only has its beak, which is attached to its face. But Jolyon Troscianko from the University of Birmingham has shown that it has two features that make the job easier: an unusually straight bill, and an extreme overlap between what both eyes can see. These physical traits set it apart from other crows and corvids, and give it an edge when using tools.

Working with Graham Martin, an expert in bird vision, Troscianko gave an eye test to 6 corvid species, to mark out their zones of binocular overlap – the areas in front of their faces that both eyes can see. For New Caledonian crows, this zone has a maximum angle of 61 degrees. For all its kin, including ravens, rooks and jackdaws, (and indeed all other birds that have been studied), the zone was less than 50 degrees wide.

To see how the crows use their extreme binocular vision in practice, Troscianko captured three wild birds and allowed them to fish for food at the bottom of a special tube. The tube contained an infrared camera that recorded the crows’ strategies.

Each bird typically held its sticks in an angled grip, so it rested against one cheek. This makes the stick more stable, and thanks to its binocular overlap, the crow can stare down the stick towards its tips using both eyes. In the images below, you can see that the far eye has a clear view of the stick and isn’t obstructed by the bill. In fact, it’s virtually looking straight down the stick, giving it a perfect view of whatever the crow is trying to extract.

The crow’s beak helps too. It’s remarkably straight. Most other corvids have a slight curve to their top bill, particularly at its tip. This bend means that other crows have to hold their sticks at a cumbersome jutting angle, like a human hand holding a pen. By contrast, the New Caledonian crow, with its straight bill, can hold its sticks so that they rest just below its eye.

Based on these experiments, it seems that New Caledonian crows have skulls that are well-suited for using tools. In an earlier study, Troscianko and Christian Rutz (a co-author on the new paper) showed that the presence of juicy, nutritious beetle grubs in New Caledonia may have driven the evolution of the crow’s tool-making prowess. Perhaps their skull shape followed suit, or maybe they already had physical quirks that predisposed them for a life of grub-fishing.

But here’s the question: Is the New Caledonian crow’s vaunted talents due to some mental advantage, or simply down to its unusual head. Or to put it another way, if other corvids had the same skull, would they also be able to pull off the same feats of tool use? “That may be spot on,” says Martin. “Certainly we have conjectured among ourselves that this might be the case,  but it would be very difficult to prove.”

The rook, for example, doesn’t use tools in the wild but can do so in captivity. “This suggests that given the right circumstances, rooks have the cognitive ability to use tools, but they do not have the [physical] adaptations which we have identified to enable these cognitive skills to be expressed routinely in the wild,” says Martin.

PS: This is not the first time that Martin’s group has discovered something deceptively simple about bird vision that nonetheless explains a lot. Earlier this year, they showed that vultures crash into wind turbines more often than other species because they have a massive blind spot in front of them when they fly.

Reference: Troscianko, von Bayern, Chappell, Rutz, Martin. 2012. Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows. Nature Communications.

More on corvids:


Comments (7)

  1. ChasCPeterson
  2. Interesting. The 2000 Caffrey paper is discussed in this one (“tool use has so far only been observed once in a single wild subject in this species”) although the 2001 paper isn’t mentioned.

  3. alanborky

    Ed this happened to me a few months back.

    I was looking out on our Liverpool UK back garden and suddenly I saw this bird which was oddly familiar yet strange until I suddenly both recognised it was a starling and realised I hadn’t seen one for over a decade if not longer though once upon a time I used to see hordes of them everywhere in the company of sparrows and pigeons.

    Anyway possibly because I hadn’t seen one in so long I was spellbound which was why I now noticed it doing this rather strange thing.

    One moment it’d have this huge fat purple worm in its beak then it’d flourish its head and suddenly the worm’d shrink and become pale then it’d flourish its head and the worm’d change become larger and red and it kept doing this so many times I found myself speculating was it somehow squeezing the worm in different ways to produce different thicknesses and lengths and colours.

    Then it revealed its secret by suddenly dropping the worm on the ground and scooping it back up except now it had at least ten worms in its beak because what it actuallyseemed to’ve been doing was pulling these worms out the ground then sorting them so as to apparently suit the carrying limitations of the shape of its beak.

    But it then pulled off one last trick.

    It snipped five of these worms in its beak in such a way that half of their bodies now dropped wriggling back to the ground before flying off making me wonder if the starling somehow knew severed worms’re capable of regenerating themselves.

    The point of this story being the only reason I saw all this was because starlings are now apparently rare causing me to pay attention to something once upon a time I’d’ve immediately looked away from.

    Ditto crows.

    When I first started using the internet at the turn of the Millennium I came across a number of scientists stating as a fact Aesop’s fable about the thirsty crow using stones to get at water was a fairy tale meant to illustrate a point about humans not birds.

    Up until I recently checked I was still reading supposed scientists saying the same thing!

    My point being Aesop made his observation over 2000 years ago and for over 2000 years apparently no scientists bothered to use their eyes or if they did they were told by their peers they were clearly mistaken and shamed into keeping quiet.

    Plenty’ll say the same thing about my own starling observation dismissing it as a mere anecdote forgetting that all reports including Darwin’s own works’re ultimately end to end anecdote.

    Even now you’re quite fairly allowing for the possibility the New Caledonian Crow’s purported intelligence might be due to its unique facial characteristics.

    But then surely the same thing could be said when you assume “Our intelligence clearly surpasses those of our primate relatives”. Are we really more intelligent or is it just our hands’re differently shaped though the opposable thumb claim went out the window for me the moment I saw a guy with no arms play a guitar with his feet not to mention a crow usie its beak to make tools by bending wires into hooks etc because otherwise by that logic Stephen Hawking’s less intelligent than a crow.

    I’m not having a go because I rather like you and your work and your authentic open minded scientific spirit of inquiry as opposed to agendaists merely stating over and over again Aesop’s just a fairy tale.

    But maybe if we’d’ve spent less of the last 2000 plus years actually observing nature rather than merely redacting the likes of Aristotle’s obsessions we’d’ve learnt long ago animals as lowly as ants and worms might not only be conscious but may in their own way be just as intelligent as us.

    For instance the ancients’ve long been mocked for believing things like humans learned housebuilding from observing bees but now not only’re bees turning out to be mathematicians but apes like Natasha’re outperforming humans on iPads!

  4. amphiox

    The question regarding whether tool use was potentiated by a difference in the brain or some physical adaptation that made it more convenient is also pertinent in human and primate evolution. When our deep ancestors first started using tools more elaborately than their close primate kin, their brains were not yet all that much bigger. So could it have been something about their hands, habitat, or upright gait that made more advanced tool using more advantageous/easier/practical for them, at that time, rather than some alteration in the sophistication of their brains?

    And could similar forces be at play in the differences observed in tool usage in the wild between the other great apes?

  5. Blathering Blathiscope

    I suppose having a beak attached to your face is better then having it attached to your butt…

    This year is the first year I have ever seen local crows taking chestnuts from trees, flying high into the air and dropping them on the road, breaking them open. Then they grab the guts and fly away to eat.

    It’s always possible that I simply missed this activity in previous years, but on the other hand we have had the driest spring and summer since they have kept records here, over a hundred years. The usual pickings might not be as good as previous years.

    They did this for an hour. I got my camera and went outside. They then stopped, for as long as I stood there.

  6. davem

    I’ve watched 5 crows playing in a high wind at the top of a hill. There was a rock there – about 60cm long and 25cm high. They were queuing up to take turns to soar the rock in the wind. As each one fell off, the next would take its place. The queue was orderly; no crow pushed his way in. This went on for several minutes. They’re brighter than we imagine. .

  7. Jess Tauber

    From a linguistic point of view, the fact that crows don’t sing may be important. For songbirds most behaviors seem to be automated, learning limited to early stages of life (that’s just my impression), while corvids, parrots, etc. are capable of real feats of learning.

    Is it possible that their calls may actually be linguistic in nature to some extent? As in the movie ‘Mars Attacks’ all we humans hear, with human-language attuned ears, is an endless series of ‘gak’s. Are their calls, for them, just syllabic carriers or syntactic contours, with all the relevant information in the subtle phonic variations?


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