“Mirror, mirror on the wall

am I the smartest of them all?”

…Is not a question crows are asking, despite what you may have heard.  Because they, like basically all the super smart birds, are really, really bad at the mirror test.

Jungle crow mirror

A juvenile jungle crow catches its reflection in a window. Photo: Paul Brown

This might contradict what you’ve heard elsewhere.  But the reality is that corvid after corvid fails the mirror test.  Except two European magpies.1  That’s right,  every sound bite you’ve ever heard that corvids possess self awareness (as evidenced by their excellence at the mirror test) is based on the performance of two birds. But more on that later.

In humans, self recognition in mirrors emerges reliably when we are about two years old and it marks the beginning of a developmental process that culminates in the rich consciousness that makes us human, at least abstractly.  Given a mirror’s significance to our own understanding of the self, it’s no surprise we’re so curious to see what non-humans animals do, and more curious still to see if it can show us whether they share our possession of consciousness.  In fact, putting animals in front of mirrors and looking for signs of recognition is something we’ve been doing, at least officially, since the 1970’s.   Since those initial studies on chimps, a debate has raged over the outcomes and overall efficacy of such tests.

A mirror test is generally composed of two parts.  The first is spontaneous self directed behaviors.  In other words, when an animal encounters a mirror for the first time, does it react like it’s looking at itself with behaviors like self exploration or does it freak out at this stranger suddenly standing in front of it?  What about after it has 100 hours of experience with a mirror or a 1,000?  The second test is known as the ‘mark test.’ A mark like a red or blue dot is applied to the animal without its knowledge and we watch and see if once it gets in front of the mirror it tries to remove or at least touch the mark.

With respect to both these tests, from African grey parrots to New Caledonian crows, we see consistent failure, or at best inconsistent maybe-kinda success.2,3 For the record, while there’s no published tests that have been done on American crows, I can tell you that I’ve watched reflective windows and car mirrors ruin many a breeding crow’s afternoon plans. In Mind of the Raven, Bernd Heinrich reports a mostly neophobic response among his captive birds, punctuated in some individuals with moderate curiosity.

So what of Gretie and Goldie, those two magpies that did show higher mark recognition when given a mirror than control birds?  There’s two problems. The first that they used stickers to mark the birds and it’s difficult to know whether it was really the mirror eliciting the behavior or if maybe they could just feel the stickers. This idea was championed after a study done on jackdaws found that birds without mirrors detected the stickers just as often as those with mirrors.4  If they had detected them equally zero times then it might just indicate that jackdaws are bad at the test, but the fact that they did detect them in both cases is what raises the alarm because it shows the birds were somehow sensing the stickers in the absence of the mirror.

The second problem is simply:  what can two birds, especially out of a sample size of five, really tell us about whether corvids understand their reflection in a mirror anyway?  Not much.

Maybe you’re thinking “well, perhaps they just don’t understand how mirrors work at all, so of course they don’t recognize themselves.”  This isn’t a bad idea but it doesn’t appear to be true.  In that study on New Caledonian crows for example, while the birds didn’t show any self recognition behaviors, they could use the mirror to find hidden food. This demonstrates that they can exploit the properties of a mirror, and understand that mirrors reflect objects in the real world.  We see the same in grey parrots.

So now that I’ve gone and dampened things, let’s just go ahead and soak the rest of that blanket.  Because even if corvids or other birds passed the mark test with flying colors, it wouldn’t necessarily mean they are self aware   which is kind of the point of the whole test.  Enter pigeons.  Since the 1980’s we’ve known that pigeons excel at the mark test with a little bit of training, just like they can excel at shape discrimination or any number of other seemingly complex tasks.5  But the ability to learn isn’t in and of itself a reflection of capacity for complex thinking.  After all, it only takes 8 days to train a spider to solve a maze.6


Pigeons in the original Epstein et al. 1981 paper

So does failing the mirror test mean corvids don’t possess theory of mind or the capacity for self awareness?  No.  Based on other studies, particularly those in ravens, it may be more likely that a mirror test, at least in it’s most common form, is just not a biologically appropriate way to ask this question.7,8  So don’t write off the capacity of a corvid to know thyself just yet.  But maybe offer a polite “ah, hem” the next time someone marvels at the narcissism of magpies.

Literature cited

  1. Prior, H., Schwartz, A. and Güntürkün, O. (2008). Mirror-induced behavior in the magpie (Pica pica): Evidence of self-recognition.  PLOS Biology 6: https://doi.org/10.1371/journal.pbio.0060202
  2. Pepperberg, I. M., Garcia, S. E., Jackson, E. C., & Marconi, S. (1995). Mirror use by African Grey parrots (Psittacus erithacus). Journal of Comparative Psychology, 109: 182
  3. Medina, F.S., Taylor, A.H., Hunt, G.R., and Grey, R.D. (2011).  New Caledonian crows ‘ responses to mirrors.  Animal Behaviour 82: 981-993
  4. Soler, M., Perez-Contreras, T., and Peralta-Sanchez, J. (2014).  Mirror-mark test performance on jackdaws reveals potential methodological problems in the use of stickers in avian-mark test studies.  PLOS ONE 9: https://doi.org/10.1371/journal.pone.0086193
  5. Epstein, R., Lanza, R.P., and Skinner, B.F. (1981).  “Self-awareness” in the pigeon.  Science 212: 695-696
  6. Punzo, F. (2000). An experimental analysis of maze learning in the wolf spider, Trochosa parthenus (Areaneae: Lycosidae).  Florida Scientist 63: 155-159
  7. Clary, D. and Kelly M.D. (2016).  Graded mirror self recognition by Clark’s nutcrackers.  Scientific Reports 6: doi:10.1038/srep36459
  8. Bugnyar, T., Reber, S.A., and Buckner, C.  (2016) Ravens attribute visual access to unseen competitors.  Nature Communications 7.  doi:10.1038/ncomms10506


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16 responses to ““Mirror, mirror on the wall

  1. Dexter Chapin

    What is the appropriate “mirror”? How does a crow differentiate among its companions? If we knew for certain that answer, could we build an appropriate, accurate doppleganger, or self-image, of a crow and measure its response?

    • Nigel

      I had the same thought. How do birds tell themselves apart? If it isn’t visually, then a mirror test isn’t going to be a good guide.

  2. Stephan Voigt

    Very interesting topic. In my opinion, however, the only thing the mirror test is mirroring is the anthropocentric way of thinking, which is still being widely used as a benchmark to ‘quantify’ characteristics and capabilities of non-human sentient beings against self-made human standards.

  3. CRConrad

    Themselves, not “thy”. Thy is the second person pronoun, like “you”. And it’s singular. So when talking _to_ a bird, _a single one,_ you can tell it to “know thyself”. But you can’t use it about some third-person birds in the plural, that’s just not how “thy” works.

  4. In reference to “other studies” in the last paragraph, I’m surprised you didn’t mention Yosef & Yosef 2010 given that, to quote Rogers/Kaplan (See “HUNTING: A CASE STUDY OF PLANNED ACTION?”, page 153 of 288), “efficient hunting in packs…requires group cooperation and it may require mind reading (or a theory of mind) of the group members and the prey (Rogers and Kaplan, 2003).”

  5. Hugo P

    The mirror test goes back to the 1970s. Long before the 2012 Cambridge Declaration on Consciousness, which was based on the latest neurological insights.

    Today, we know that most animals that reproduce sexually are self-aware. If you need some-body else, you need to distinguish between concepts like other plants, stones, enemie-bodies and mate-bodies. If you have a shared nervous system and a hormonal system like all fish, mammals, and birds do, you can assume a similar evolutionary consciousness. Similar in type and not degree.

    The mirror test, like aether in physics, was well meant but has long served its time. Most animals scare when they first encounter a mirror. Most animals stop to scare once they accept that not only water on the ground can reflect their image. They prove that they do not assume a doppelganger by using mirrors to get to hidden objects.

    The mark test is potentially a good test to see how much an animal knows what he or she her- or himself look like and if they care about looks, but not much more. Animals who do not know what they look like are not less self-aware. Animals who do not care what they look like are also not less conscious etc. If you teach them, aka communicate a good enough reason for an action, they will pass mark tests left, right and center. A good reason differs from individual to individual, not just species to species.

    Last but not least, many birds like corvids can see UV light. Most mammals cannot. Birds use UV to e.g. distinguish between sexes like blue tit research has shown since 1999. Blue Tits females and males might look similar to us but they don’t to the birds.

    Most conventional mirrors have aluminum on the back side of the glass and hence they absorb a lot of UV light. Are we certain we get what birds are seeing in mirrors? We humans are not less self-aware because we cannot see UV light. Birds are not less self-aware because they can see UV light.

    • Hi Hugo. Seems like you put a lot of thought and effort into this post, but I’m not sure why you found it necessary to re-explain several of the facts/concepts that I included in the original article. It’s also not true, at least scientifically, that we would describe most animals that reproduce sexually as being self aware. You are welcome, however, to debate the merits of that reality as much as you like though.

      • Hugo P

        I really appreciated your article! I wanted to add to what you said. I wanted to wonder aloud why the mark test is still a thing when it comes to self-awareness at all? Who funds this? Reading about recent and ongoing mark tests stroke an obvious nerve with me 😉

        E.g. The magpie test was conducted in e.g. 2008, crows in 2011 and now there is a 2016 study our. What? They are still testing for self-awareness and not eg narcism. Again, as if we did aether tests today? Will later human generations use the mark test to discuss the limits to humans intelligence? Are we smart enough to see how smart animals are, de Waal wonders?

        My long post was hence about the mark test and not consciousness or self-awareness per se. The Cambridge Declaration of 2012 has done a fine job regarding self-awareness in most animals. Self-awareness is something very basic and old hat does not require special intelligence or evolution. If you are animated, chances are you are self-aware and realize your own movement in contrast to your environment. If you can judge another animal’s feelings, angry or happy, attacking or fleeing, you already have all the self-awareness of humans. The mark test is about sight and esthetics, not self-awareness. Why do you think that the mark test is still a thing in 2016 for self-awareness? I get animals most of the time but I am really curious to understand the humans who study them better.

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