Crows Understand Cause and Effect, Even When the Cause is Hidden

By Sophie Bushwick | September 19, 2012 2:36 pm

New Caledonian crow

For the New Caledonian crow, birdbrain is a misnomer: These members of the corvid family have proved their problem-solving and tool-wielding abilities again and again. The birds may have yet another impressive cognitive capacity, a new study suggests: causal reasoning. The ability to link an event with the mechanism that caused it, even if that mechanism is hidden, is the basis of modern science—and our most basic knowledge of the world around us. If New Caledonian crows are capable of causal reasoning as well, we can better trace and understand the evolution of this ability.

Researchers described how they tested the crows’ reasoning in the Proceedings of the National Academy of Sciences. First, they let eight New Caledonian crows figure out how to use a tool to remove food from a hole in a box. Then the experiment began. The crows watched as a human entered their enclosure and stood by the box. But this motionless figure, eyes closed and hands in a neutral position, did not pose as much of a threat as the blue cloth hanging over one side of the enclosure. Through a gap in this bird blind, a stick emerged and poked at the hole in the box 15 times. Finally, the stick stopped moving and the non-threatening observer left the aviary.

Because the birds had to turn their heads away from the bird blind—where the probing stick had emerged—in order to nab a treat from the box, they were understandably cautious after the stick withdrew. Although they gradually went back to extracting food, they first inspected the bird blind and abandoned some preliminary probes of the food box. However, the birds were less wary and exhibited less testing behavior when they saw a second human enter the bird blind before the stick started moving, and leave the blind after the stick’s motion stopped. They recognized that the hidden human was the cause of the moving stick (even though, for consistency with the single-human situation, the stick was actually under the control of an experimenter outside the enclosure).

Understanding that a human was moving the stick, and that it would stop moving in the human’s absence, is more than a knowledge of cause and effect. Because the experimenter was invisible behind the bird blind, the crows did not actually see anyone moving the stick. And yet they could still infer that the human presence was responsible for the stick’s motion, which indicates that they can recognize even a hidden causal agent. This is a very impressive ability—until now, the authors write, “Although [research had suggested] animals can reason about the outcomes of accidental interventions, only humans have been shown to make inferences about hidden causal mechanisms.”

Image courtesy of John Gerrard Keulemans / Wikimedia Commons

CATEGORIZED UNDER: Living World, Mind & Brain
  • Alex

    You can see a video of the researchers explaining their experiment here:

  • JMW

    I’m not sure I buy this. The crows may be connecting the presence of a human with the stick, but not inferring the presence of another human behind the blind. In other words, it may be as if they are thinking, “a stick pokes out only while a human is beside the box”, not “there’s a hidden human behind the blind moving the stick, but only when there’s human by the box.”

    I think a better test would have been to have a human cross the enclosure to hide in the blind, and then have this person poke with the stick. Observe the behaviour of the birds. Do they approach the box after the human crosses the enclosure? Do they approach the box after the human leaves?

    Then, really cross them up. Have the human cross the enclosure, hide in the blind, and NOT poke with the stick. What do the birds do then?

  • Kevin S.

    Except that the crows exhibited less testing behavior when they saw a second human enter and leave the blind. If they were just reacting to the presence of a human beside the box, there should have been no significant difference in their behavior whether or not they saw a person go into the blind. Since there was always a human beside the box in all trials, the results are telling.

  • John Lerch

    This isn’t cause and effect, it’s CORRELATION. Correlation is a necessary correlate of cause and effect, but it’s not sufficient. IOW the birds understand
    IF statements
    but there’s no knowledge about
    IF and ONLY If statements.

  • albrt

    So I guess the evolved inability to distinguish correlation from causation runs all the way from science writers to avians. That’s worth knowing.

  • Gepap

    @John Lerch:

    Even if this test only shows the Crows can figure out IF statements, that is a greater level of understanding than humans are generally willing to give animals. And sadly I have met plenty of humans incapable of really understanding If and ONLY if statements.

  • Crow Flies

    They attribute the crow’s recognition of a hidden causal agent because the human in the enclosure did not wield the stick himself. The stick moved without visible cause, the human was just standing there. The crows linked the stick and the human together but observed that the human himself was not the one wielding the stick.

  • m

    I have seen i believe it was 6 crows work together, by swooping and knocking the head of a giant rat, one after the other dive bomb, hit and fly off, then when the rat slowed in it movement they landed and finished it off with more hits to the head.

    Then they shared a meal.

    I went over, they stepped back about a meter so i could see, watched me, then i walked away and they went back to eating.

    There was a lot of consciousness in the crows I saw…a lot.

  • ignatius

    Not surprising in the least. Much too slowly than is prudent or humane, we are beginning to learn that other earthlings, merely non-human in exterior shape, are just as important as we think we are. Those who continue to resist “comparing” non-humans to ourselves, and think any sub-human intelligence discounts their value, do so only so they can continue to justify their mistreatment and enslavement of them–in the name of science. Godwin’s Law invoked: Dr Mengele did the same.

  • Eats Wombats

    Hmm. I had a pet crow (Corvus cornix) as a boy who exhibited a lot of intelligence but not tool use. He used to pull the dog’s tail, then when it turned around from a bone it was chewing to bark at him, then jump over it and land on it and steal it if it was light enough. He used to wait outside the back door for my mother to go out to put clothes on the clothesline, nip in past her, steal coins from a windowsill in the kitchen, then nip out as she re-entered the house (I caught him once; he’d been doing it for a while–I found his hoard). I could go on. I think he had some very clear ideas of cause and effect and he recognized individuals and treated them differently. Smarter than any dog I’ve had since. Actually, he did sorta use tools. He tore up newspaper and used it to conceal his stashes of valuable stuff (coins, food, silver paper, shiny things). And he ‘supervised’ my father in the garden when he was planting things-checked the holes for bugs before seeds went in.

    Ted Hughes’ poem Crow is an epic tale for anyone with an affection for these feathered swaggerers.

  • Crow Mag Numb Man

    That’s funny to hear about the mind of a Crow. Because there is a crow in a tree of my neighbor’s yard and I have been feeling for quite some time that it is literally trying to tell me something. I dry my clothes on a clothsline in my back yard and that same Crow start’s squawking almost like he is speaking a language that he want’s me to learn? I know it sounds weird but after reading this article I do believe they are much more intelligent then we have been led to believe. Since this bird only does this when I come outside I have been thinking that he is a reincarnation of someone. I honestly felt like it was my mother? This is/was her house for 60 years and she’s been gone for 11 years. Just the other day I felt like she was squawking at me, and I honestly felt I understood that it was telling me , “Why are you drying your clothes outside? What’s wrong with the dryer?…. very weird. well not that weird considering all the other things, mainly this computer keeps telling me. Telling me things that are Really weird but in fact are Real….I just had to write this down when I seen the Crow….or is mine a Raven…..or a magpie? whatever a magpie is?…..These are things inside my mind….Anyway Hi, Mom, I don’t have a dryer!…


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