Do crows, like humans, have a concept of “hidden causal agents”?

September 23, 2012 • 6:08 am

It would obviously be adaptive for some animals to be able to distinguish between natural phenomena, like wind, and phenomena that have similar effects but are caused by hidden agents like predators.  One example (used in the paper below) is the rustling of trees in a tropical forest canopy.  We know how to distinguish between the rustling caused by wind, which is general, and the rustling that is localized and moves slowly, like that caused by a troop of monkeys moving through the trees. (I experienced this myself on a recent trip to Costa Rica). If you’re liable to be disturbed (or eaten) by monkeys you need to pay attention to avoid the troop, but in the case of wind you don’t want to waste valuable foraging time looking up and getting nervous every time a leaf rustles.

This notion of “hidden causal agency,” of course, has been suggested as a pivotal factor in the origin of religion. If you’ve read Pascal Boyer’s provocative book Religion Explained, you’ll remember his thesis that before humans understood natural phenomena (e.g., thunder, lightning, or tree rustling), it was natural for them to impute them to causal agents—supernatural ones.  This was, he thought, a “spandrel” piggybacking on our evolved notion to be alert, and to mentally ascribe natural phenomena to things that could either help us or hurt us.  (For example, it’s better to think that a rustle in the bushes is a predator than to ignore it, even though there’s a “false positive” cost of interrupting your tasks because you’re hyper-alert. But better to be hyper-alert than to ignore a rustle that could kill you.) And that, says Boyer, ultimately led to religion: the ultimate belief in hidden causal agency.

So far the only animal shown to have the ability infer hidden causal agency is Homo sapiens. A dog lover told me that he’s absolutely sure that dogs can do it (caninophiles attribute all sorts of wisdom to dogs in the absence of any scientific evidence!), but so far there have been no studies demonstrating this.

Such tests are, however, possible.  One was recently conducted in New Caledonian crows, Corvus moneduloides.  These animals are awesomely smart, and in fact are the only non-human species known to modify non-natural materials in the lab to make tools for procuring food, and to use other tools in ways previously seen only in primates (go here for a good description of three kinds of crow tool-use).  Here’s a video of one of these smart beasts figuring out how to retrieve food by bending the tip of a wire into a hook. It’s amazing:

At any rate, a group of researchers at the Universities of Auckland, Cambridge, and Vienna wanted to figure out if these crows had the notion of hidden causal agency. The method was, as the authors note, “to infer what caused an inanimate object to move.” The results, described in a new paper in the Proceedings of the National Academy of Sciences by Alex Taylor, Rachael Miller, and Russell Gray  (free access and download at link), suggest that crows can indeed infer hidden causal agency.

The study involved using 8 crows trained to use a stick as a tool for retrieving food. The experimenters then put the food-retrieving apparatus on a table in front of a curtain. The curtain had a hole in it through which a stick could protrude.

Then, each crow was given three sequential “hidden causal agent” (HCA) trials: a human walked into the room behind the curtain (in all trials there was also another human standing in the corner of the room), and then the stick was pushed through the hole, protruding near the food apparatus, 15 times. (The movement was controlled by pulling strings, usually by someone outside the room, so the stick always moved the same way.)  After the crow saw this, the human (and the person in the corner) then left the room, so that the crows could go back to their food-retrieving setup.  (They don’t do that when the stick is moving because it could hit them in the head.)

Here’s what the experimental setup looked like (figure 1 from the paper):

After the crows had experienced causal agency, and saw that the stick stopped moving when the observer left the room, each was given three trials with an “unknown causal agent” (UCA).  A person came in and stood in the corner of the room, as before, but nobody came in and went behind the curtain. The stick was again moved 15 times in and out of the hole by the person outside the room. Then the stick stopped moving, and the observer outside the curtain also left the room, as he did before:

To see whether the crows were worried that the stick would move, and attribute that to the man behind the curtain, the experimenters measured how often the crows “inspected” the hole, that is, how often they looked toward it and abandoned their probing for food, seeing if the stick might come out and poke them.  The definition of “inspection” is in the paper, and the behavior is clear in the video below.  Here’s their predictions, which differ based on whether or not the crows habituate to a causal agent:

If the crows could attribute the stick’s movement to the hidden human, they could infer that when the human left the room, the stick would not move again. In contrast, in the second, unknown condition, if the crows were capable of causal reasoning, they would predict that the stick might move again because they had not observed a potential causal agent leave the hide. This “causal reasoning hypothesis,” therefore, made the opposite prediction from the “habituation hypothesis” outlined above. In the hidden agent condition, the crows should show similar levels of caution to those in the final trial of habituation to the hide. In the unknown condition, the crows should show a high level of caution, despite the movement of the stick no longer being a novel stimulus.

Here are the results, which graph the number of crow “inspections” (i.e., when they abandoned probing to look at the hole). The results are divided up for the initial “habituation trial” (with no stick moving), and sequentially for the three HCA trials and then the three UCA trials:

Fig. 1. Inspection rate across conditions. Final habituation trial before
testing is indicated by 20cm hab. (Upper Left ) Diagram of the HCA condition.
(Upper Right) Diagram of the UCA condition. In the HCA condition, one
human walked into the hide and one stood in the corner of the room. A
wooden stick was then probed from the hide. The agent then exited the
hide. Both humans then left the room. In the UCA condition, one human
entered the cage and stood in the corner. The tool was then probed through
the hole. The human then left.

What you see is that when the human was behind the curtain and then was observed to leave, the rate of inspection after the crow goes back to its food-box is low, and remains low. (It is in fact equal to the “habituation” trial when there was no stick poking out.)  But when the stick moves and a human wasn‘t in the room (UCA trial), the rate of inspection is significantly higher than in the HCA trials, at least for the first two of the three UCA trials (there appears to be some habituation in the latter trials).  The higher inspection rate is presumably because since the crows didn’t see a human come in and then leave the curtain, they were worried that somebody was still behind the curtain moving the stick, and they remained nervous that they might get poked. As the authors say,

These results show that New Caledonian crows, like humans, can attribute an observable event to a hidden causal agent. When the stick moved while a potential agent was in the hide, and that agent then departed, the crows had a relatively low inspection rate. All of the crows we tested, however, increased their inspection rates after observing the stick move when no potential causal agent was present. In fact, inspection rates were far higher in the first trial of the unknown agent condition than in the first human agent trial. This was despite the human trial being the first time the crows had observed the novel stimuli of a stick emerging from the hide and a human entering and exiting the hide. Similarly, no crows abandoned probing and left the table when the stick emerged from the hide for the first time, but some did when the stick’s movement could not be attributed to a causal agent. Given the probing stick was a novel, aversive stimulus to the crows, a purely associative account would struggle to explain why the crows reacted to this stimulus in the unknown causal condition but not in the human condition. This pattern of results is, however, predicted by a causal account of the crows’ actions: the crows attributed the movement of the stick in the human condition to the agent inside the hide and, so, inferred that the stick was unlikely to be probed again once the human had left the hide. In the unknown condition, there was no recently departed causal agent to attribute the movement of the stick to, so the crows reasoned the stick could be probed again.

I’ve heard that there are criticisms of this experiment on the internet, though I haven’t looked for them (alert readers might try). But it looks at least suggestive to me, especially in light of the known intelligence and reasoning ability of these birds.

Here’s a new video in which one of the authors, Alex Taylor, explains the experiment and shows the setup (it also shows what they mean by a crow’s “inspection”). Maybe I wasted my time writing all that stuff above!

As the authors note, they’re not the first to speculate that some species can impute agency. As the authors note, Darwin conjectured this in The Descent of Man:

Darwin himself speculated that a dog barking at a parasol moving slightly in a breeze might be because the dog reasoned that “movement without any apparent cause indicated the presence of some strange living agent.”

Well, I’m not convinced that dogs have the notion of causal agency, or are even as smart as crows (dog-lovers, don’t attack me, but wait for experiments before you assert your pet has a concept of agency!).  But it’s possible that this notion is far more widespread in animals than we think, and experiments like the one above are the way to show it. They’re not that hard, actually, and I suspect more will be done soon.

In the meantime, when you see a crow—because they’re all smart—give it a wink in recognition of a fellow intelligent being.


Taylor, A. H., R. Miller, and R. D. Gray. 2012.  New Caledonian crows reason about hidden causal agents. Proc. Nat. Acad. Sci. USA, published online before print September 17, 2012, doi: 10.1073/pnas.1208724109

36 thoughts on “Do crows, like humans, have a concept of “hidden causal agents”?

  1. You have no arguments from me: the crows that hang out at my bird bath are very smart, and it nice to see research into animal smartness.

    I have observed them (a mother and offspring) fly in with dried bread from some bin somewhere, soak it in the water to soften it, and then eat it. If they have too much, they will store the bread either under the mulch in the front garden, or stash the bread in some miniature conifers that I had planted around the bird bath. In order to protect the stored bread, the crows even place rocks on top of the bread in the conifer plants so it is hard to remove.

    I have even seen them leave cane-toads to soak in the bird bath water for a day or two (on a personal note: yuk!) to soften it up. Ie: cooking! I don’t know if the soaking dilutes the poison out of the toads, as cane-toads are very poisonous, but they do eat them once they are “ripe” (ugh: I have to clean that bath – come on guys!)

    They are not 100% clever though: I have seen them have a bath in the water (very amusing – so cute) then fluff themselves on the edge of the bath. Calmly poop in the water, and then fly off. The next day the water is too yucky to bathe in, so I have to clean it… again.

    1. “They are not 100% clever though: I have seen them have a bath in the water (very amusing – so cute) then fluff themselves on the edge of the bath. Calmly poop in the water, and then fly off. The next day the water is too yucky to bathe in, so I have to clean it… again.”


      Do a poo in the water, next time you come back the water is clean. Certainly not daft behaviour!

      1. Nope… I don’t clean it that often 🙂

        I can leave it for days and they won’t bathe in it. They still soak food in it though. I guess they don’t bathe as the water would gum up their feathers (yes it gets that ba sometimes)

        I am sure they watch me clean it though, as it is not long until they are back again. Watching… always watching. With those blue eyes.



      1. Hmm, I was going to guess “humans,” but mostly they don’t seem that smart (cue statistics on belief in creationism).

  2. Much of what you see with crows, and other creatures, can be accounted for in terms of learning correlations. We need not jump to the conclusion that they have concepts of hidden causes.

    Concepts, as we normally understand them, are very much tied to the use of language. As far as I know, crows don’t have anything comparable to human natural language.

    1. There are many, many ravens in my area of the Manzano mounains. I don’t think they have “language” as we know it, but they have a HUGE range of vocalizations. L

    2. Concepts, as we normally understand them, are very much tied to the use of language. As far as I know, crows don’t have anything comparable to human natural language.

      Do we really need a fully developed language for having a concept? Maybe some rudimentary ability to manipulate abstract symbols is enough. It seems clear that in order to think about concepts you need language but just having them may require less. I vaguely remember reading somewhere that some animals have a rudimentary ability to do “math” I’ll see if I can find the reference.

      1. Do we really need a fully developed language for having a concept?

        I did include an “as we normally understand them” clause. We build our concepts in a cultural environment that is made possible by language.

        Sure, I expect that could be simpler things that play some of the cognitive roles of concepts, but that are not dependent on language. We probably have many of those but are unaware of them.

  3. I don’t know if this qualifies as a hidden causal agent, but I have a large fan in my barn, which I turn on when it gets too hot for the goats to be comfortable. The switch for the fan is in the garage, on the other side of the wall from where the goats can see me turn it on.

    The first couple of times in the summer when I use it, they all jump and run out of the barn before they come back in to congregate in a big pile right in front of it.

    After that, they don’t even look up when I turn it on, except to move to their spot in the breeze. L

  4. “This notion of “hidden causal agency,” of course, has been suggested as a pivotal factor in the origin of religion.[…by Pascal Boyer]”

    Boyer, IMO, makes the correct !*psychological*! observation which is illegitimately turned into a !*philosophical*! argument by Alvin Plantinga in “God and Other Minds”.

    However, Plantinga will not “eat crow” after reading Boyer.

  5. Dayum. That’s one smart bird species – of course, if Ceiling Cat loved birds as much as He does humans, birds would have opposable digits (and way snazzier feathers).

    I often wonder when my cat stares at me what (besides the desire to bite my eyelids – she’s an eyelid nibbler) is going through her ‘mind’.

  6. So far the only animal shown to have the ability infer hidden causal agency is Homo sapiens.

    That’s actually pretty mind boggling, that not even our closest relatives have this. I wouldn’t have guessed that, since some animals appear to show some basic Theory of Mind skills. It doesn’t seem that this should be that far removed – interesting.

  7. Does this mean that I now have to worry about offending crows when I dismiss supernatural explanations?

    Thing that snuffies in the military are taught:

    You hear “crack, crunch, crack crunch” at continuously changing bearing to you: whatever it is either doesn’t know you’re there or doesn’t care.

    You hear “crack” [pause] “crack” with both noises in approximately the same place. Whatever it was stopped for a moment after making the noise. It might be trying to be sneaky and it might be interested in you.

  8. This thread reminded me of “Silverspot, The Story of a Crow” by Ernest Thompson Seton, part of his series called “Wild Animals I Have Known.” One source is An example of crow intelligence, perhaps apropos to the topic at hand, occurs about midway through the story: Silverspot accidentally drops a piece of bread into a stream, which disappears into a culvert. “Thinking” swiftly (per Seton), the crow flies down to where the stream reappears in the open and seizes the bread when it shows up again.

    1. I remember reading that as a teenager growing up in north Toronto. The place names that Seton mentioned as being rural or wild were in my area, but they were all suburbs by my time.

  9. Crows also have a very well-developed sense of ‘unhidden causal agents’

    in a study, someone wearing a mask captured and banded crows from nests (which the crows of course resent), and for years afterwards anyone who wore the mask would be harassed and mobbed by crows, many of whom had not been original victims. The birds taught each other who the bad guys were.

    So they already have a somewhat abstract sense of danger, in that they can associate it with behavior of other crows, not just original stimulus. I wonder if this is a prerequisite for the ‘hidden causal agent’ phenomenon.

  10. Experiments with animal behaviour are so interesting. I’m very impressed with the ingenuity of researchers to be able to design such experiments.

  11. Here is a probably naive question:

    Does this type of behavior in crows, as well as other recent studies on animal “psychology” such as recognizing death, form another bit of evidence for evolution and against creationism?

    (I recognize that evolution is neither purposive nor progressive; in what follows I’m struggling to express my question clearly). What I mean is, if evolution makes (some) species progressively more intelligent (because intelligence has survival value), then in the history of the world we would expect to see the gradations of intelligence from the negligible (dogs), up through squid and cats, to the truly intelligent crows, dolphins, and chimpanzees (is there anyone left whom I have not offended? ;-), that we actually do see, in a manner somewhat analogous to the wide range of eyes that exist in nature.

    On the other hand, the set of qualities which we could group together as “abstract thought” (recognition of hidden agents and death, language, etc.) are usually attributed by creationists to the “soul”; since by their own definition, only humans have a soul, creationists say that only humans can have these qualities. If animals seem to exhibit them, so the creationists say, that is only hardwired, instinctual, mechanical behavior.

    Hence, if it can be shown that cats, crows, or chimps really do have the capacity to “do what only humans can do”, don’t we have a modus tollens refutation of creationism, thus:

    P: Creationism is true.
    Q: Only humans can recognize hidden agents (and exhibit other attributes/behaviors of the “soul”).

    The creationists say “P implies Q,” the scientists show “not Q” and we conclude “not P.”

    Is this argument worth the electrons it’s printed on?

    1. I think your reasoning makes sense, although I doubt an argument like this would move a creationist at an intuitive level. For that to happen you’d probably need a gradation of animals, showing cognitive skills at various levels (maybe that of, say, a human toddler) all the way up to humans. Impressive as it is, the crows in this study show just tiniest sliver compared to the human capacity for reasoning.

      I’m not really up on the Sophisticated Theologian debate, but I think this is indeed one argument that’s still used – the idea that humans are so strange when viewed in light of the animal kingdom. The types of cognition that allow for complex language, learning, social cooperation, scientific thought, self reflection, and so on, are still not entirely understood, but it seems safe to say there are plenty of areas (in human minds,) in which we find no real parallels anywhere else. The human mind really is an amazing thing, and like consciousness, I think there’s still enough “WTF!” (for want of a better term,) factor there to allow Sophisticated Theologians to appeal to the God of the Gaps argument in this case.

  12. Long time reader, first time commenter here. I wanted to let you know I read almost all your posts, barring the occasional one about sophisticated theology, since I’ve been heavily steeped in that for a long time.

    I think a lot of people read your posts on biology. Probably just as much as any other subject. Personally, I just don’t feel qualified to say much on biology. You are the master of this subject and I am a learner. I have some background in all the sciences, but nothing compared to your vast knowledge and comprehension. Therefore, I typically just read what you post on these things and think about them for a while.

    When you post about politics or about religion and atheism, I feel much better qualified to say something. I also have an opinion on the subject. I think this is the case for many of your readers. Even a lay person can have a lot of insight into religion or politics, but I think that sort of insight is much rarer in a scientific field.

  13. This is an interesting study. What I find more interesting is the absence of critique anywhere. Neil Rickert has it correct. I think it a stretch to interpret these results as the crows making inferences about hidden causal mechanisms.

    This research has relevance to my own thesis. I think I should write a more careful review of it myself. I’ve read the original, and there is far too much taken for granted.

  14. Add me to the “not surprised by anything crows do” faction. I’ve been observing off and on a breeding family of crows on my property for a few years now. In addition to everything else already mentioned, their social and family structures are complex and vital. I’ve observed the individual in this video for several weeks now; I doubt very much if it would have survived without the support of its extended family:

    As Linda Grilli Calhoun observed about her ravens,crows too have an enormous repertoire of vocalizations. They are also wonderful mimics. This spring I watched one practice over and over the call of an owl and the sound of a woodpecker pecking. Were I better at recognizing those sounds I could probably tell you just what species it was imitating. A birder who feeds crows, and said hello everytime he encountered them, was delighted one day to have a crow say hello to him.

    In general, the idea that animals could be able to differentiate random from non-random stimuli, esp. the harmless from the potentially harmful, should hardly surprise biologists given how hugely adaptive such responses are. Surely there’s some innate ability to put 2 & 2 together like this without invoking any cognition whatsoever. Which is not to say this cool study doesn’t measure what it says it does, just that it sounds to me as if the null hypothesis is typically inapt.

    1. The over-complicated noun-phrase concept of “hidden causal agents” deserves to be smashed into smaller pieces.

      (E.g., it seems pretty obvious that the crow’s behaviour is oriented to the hiding place, which means the agent in there is not exactly ‘hidden’.)

      How about this one: “Do crows tend to avoid being poked in the back of the head when the poking action is trivially predictable?”, followed by “What if we make it a bit less easy?”

      Or, if obscurantism is preferred, why not ask: Do crows, like humans, have a sensus divinitatis?

  15. Last night I left the screwdriver that moonlights as the key to my bedroom door inside the room when I locked it. Having no similar tool, I had to fashion a makeshift flat-head from a paper-clip using pliers to bend it into shape. Upon success my immediate reaction, having forgotten who caused the problem in the first place, was “I am genius!” Watching then the first video of the crow fashioning the wire into a hook without the benefit of opposable thumbs or needle nose pliars, the wind has most certainly left my sails.

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