A typical adult human recognizes that the image one sees in a mirror is oneself. We do not know how much training a mirror-naive adult requires to do this, but we think very little.
When a typical adult macaque (a species of monkey) looks in the mirror, it sees another monkey. Typical adult male macaques stuck in a cage with a mirror will treat the image as a fellow adult male macaque until you take the mirror out of the cage.
(Experiments that attempt to determine if an individual can recognize themselves in the mirror ultimately derive from what is known as the Gallup Test, after Gordon Gallup, who first painted spots on the foreheads of primates to see which individuals .. of which species ... figure out that you can inspect one's own forehead by looking at one's face in the mirror.)
A typical adult chimpanzee will be startled by the mirror on first encountering it, or show curiosity, maybe exhibit bewilderment. But within a very short period of time, the chimpanzee will realize that this is an image of self.
A chimpanzee that understands that this is an image of self will use the mirror to inspect his or her own body, to see things never seen before, will identify bits of lint or paint stuck to the face and groom them away, and so on. Placed with a group of mirror-naive chimpanzees, the chimp that understands mirrors already may try to freak out the other chimps by showing it the mirror. They seem to get a kick out of this.
Magpies do this too.
A Repost
Well, the magpies don't try to freak each other out, but they do "get" mirrors, according to a study recently published in PLoS Biology (Mirror-Induced Behavior in the Magpie (Pica pica): Evidence of Self-Recognition) From the author's summary:
A crucial step in the emergence of self-recognition is the understanding that one's own mirror reflection does not represent another individual but oneself. In nonhuman species and in children, the "mark test" has been used as an indicator of self-recognition. In these experiments, subjects are placed in front of a mirror and provided with a mark that cannot be seen directly but is visible in the mirror. Mirror self-recognition has been shown in apes and, recently, in dolphins and elephants. Although experimental evidence in nonmammalian species has been lacking, some birds from the corvid family show skill in tasks that require perspective taking, a likely prerequisite for the occurrence of mirror self-recognition. Using the mark test, we obtained evidence for mirror self-recognition in the European Magpie, Pica pica. This finding shows that elaborate cognitive skills arose independently in corvids and primates, taxonomic groups with an evolutionary history that diverged about 300 million years ago. It further proves that the neocortex is not a prerequisite for self-recognition.
(A) Attempt to reach the mark with the beak; (B) touching the mark area with the foot; (C) touching the breast region outside the marked area; (D) touching other parts of the body. Behaviors (A) and (B) entered the analysis as mark-directed behavior; behaviors (C) and (D) and similar actions towards other parts of the body were considered self-directed, but not related to the mark.
Self recognition is known in the apes and not generally in primates. However, it is ascent in very young human children (and probably all very young apes) and present in at least one species of non-ape primate (the black and white tamarin, a sort of New World monkey).
It is seen in elephants, and now it is seen in magpies.
What do these animals all share? Well, not a neo-cortex, exactly, so that may not be the "seat of self recognition" ... All these creatures seem 'smart' but so do some other species that don't seen to be able to do this. All are good at problem solving.
There is probably not a single clear and simple link between this ability and the cognitive capacities of any organism that has it. Mirrors do not occur in nature, so this test is measuring something in an abstract and arbitrary way. Therefore, even though we can divide the world of animals (vertebrates, really) into those that recognize themselves in the mirror vs not, we are not really dividing these species into those with a particular trait versus not. Passing (or not) this test does not indicate a particular trait, necessarily . It indicates something, but the test should be presumed to be insensitive to the specific nuances that would separate, for instance, bird from monkey or elephant from ape.
Clearly, this needs to be tested in more bird species..
Prior, H., Schwarz, A., Güntürkün, O., de Waal, F. (2008). Mirror-Induced Behavior in the Magpie (Pica pica): Evidence of Self-Recognition. PLoS Biology, 6(8), e202. DOI: 10.1371/journal.pbio.0060202
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Hmmmm. This explains why PZ's basement is full of aquariums, each with a different kind of octopus and a mirror.
Mirrors do not exist in nature but you can get a reflection off a pool of still water.
And guess what this behavior totally looks like:
http://www.youtube.com/watch?v=9lB5_X_QXlU
I don't know if my cats understand mirrors, but they sure don't seem to act like it's another cat in there. They react pretty strongly to other real cats, and mostly ignore the mirrors.
Facinting article, Greg!
@Nemo, my cat does the same thing. She hates other cats and reacts strongly to their presence. She doesn't care if she smells another cat, as long as it's not there.
There is one time I think she reacted to her reflection (in the window) and she was already in attack/protect mode, as she saw another cat outside the window that she perceived wanted to invade her territory.
So, my conclusion is that some cats can probably recognize this, but can lose the ability to "think rational" when certain instincts kick in.
Bjorn@3 - so that's where the Ministry for Silly Walks came from! (not to diminish John Cleese's excellent development).
I have seen some dogs that cannot seem to control their aggression toward the mirror and some who quickly learn to ignore it. I don't know if they click to it being a reflection. Probably not. But then what do they think?
I have seen mocking birds attack a mirror for hours until I had the mercy to cover it. I have not seen a crow attack a mirror.
What about other animals generally considered to be intelligent? Octopi, dolphins & whales etc.
I don't think cats do get it, though I haven't tried putting a dot on my cat to test it. Usually when you put something on your cat they don't need a mirror to know it's there. I always thought that the reasons cats don't generally respond to mirrors is that they can't smell another cat...
objlolcat: http://icanhascheezburger.com/2010/08/15/funny-pictures-rex-freaked-out
I have often put a small freestanding mirror on the floor near a young cat or kitten who hasn't encountered mirrors before and the usual reaction has been to investigate the stranger visually and then to go behind the mirror to find it. When no cat is found he or she will (apparently) conclude that there really is no other cat to worry about (or play with) and proceed to ignore it.
However, I do now have an adult Persian who likes to jump up on our sideboard and stare into the large mirror that hangs over it. I often find that if I look into the mirror from an angle I will see the image of the cat staring at me. It's as if he is trying to figure out who this other person is who looks like me.
But, to get back to the subject, I have never seen a cat recognize itself.
They have to learn mirror smarts because I've seen jays and ravens charge and peck at their reflections in windows.
I also got to watch a jealous cardinal furiously attacking my outside rear view mirror one day...not a corvid but good for a free grin.
I have seen some dogs that cannot seem to control their aggression toward the mirror and some who quickly learn to ignore it. I don't know if they click to it being a reflection. Probably not. But then what do they think?