What Animals See When They Look in a Mirror
Some attack it. Some ignore it. A very few realize they are looking at themselves, and the list of those that do is short and full of surprises.
Videos of wild animals meeting a mirror in the forest are irresistible. A leopard snarls at it. A gorilla charges. An elephant studies it for a long time. At home, a puppy barks at the hallway mirror and a cardinal spends all of April fighting the side mirror of the car.
Behind the entertainment is a serious question that scientists have been testing for more than fifty years. Does an animal know that the reflection is itself? To us the answer seems too obvious to need thought, but a mirror is a strange object. It shows an animal that moves when you move, has no smell, makes no sound, and can never be reached.
Understanding that image takes a particular mental step. The animal has to grasp that the body in the glass is its own body, seen from outside. Only a small number of species take that step, and they are not always the ones you would guess.
Here is what the research shows, what it means for the dog and cat at your feet, and what to do about the bird that will not leave your window alone.
Read all the way to the end. The last section explains why failing this test may mean nothing at all.
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The experiment
1. The mark test
Has your pet done this?In 1970 the American psychologist Gordon Gallup Jr. published a short paper that started the whole field. He had given young chimpanzees a mirror for ten days and watched what they did. At first they treated the reflection as a stranger, with threats and calls. Within a few days that stopped. They began using the mirror to look at parts of themselves they could not otherwise see, picking at their teeth and inspecting their own backsides.
AdvertisementThen came the clever part. Gallup anesthetized each chimp and put a spot of odorless red dye on one eyebrow ridge and the opposite ear, places the animal could not see directly. When the chimps woke and were given the mirror again, they looked at the reflection and reached up to touch the marks on their own faces.
Monkeys given the same test did not. They went on treating the reflection as another monkey.
AdvertisementThe procedure became known as the mark test, or the mirror self-recognition test, and it has since been tried on dozens of species.
A mirror shows an animal that has no smell, makes no sound and can never be reached.
Try thisPut a small sticker on your own forehead without looking and then step in front of a mirror. Your hand goes straight to your own head, not to the glass. That reach is what the test looks for.Advertisement -
The apes
2. Our closest relatives, and our own children
Has your pet done this?The great apes are the most reliable passers. Chimpanzees, bonobos and orangutans recognize themselves again and again in studies. Even so, not every individual passes. Young adult chimpanzees do best, while infants and elderly animals often fail.
Gorillas are the exception. Most fail, which puzzled researchers for years, since gorillas are every bit as intelligent as the others. The likely reason is social. Among gorillas a direct stare is a threat, so a gorilla avoids looking the reflection in the face and never studies it long enough to work out what it is. Gorillas raised closely with people, such as the famous signing gorilla Koko, have passed.
AdvertisementHuman babies go through the same stages as the chimps. In the version used with children, a parent wipes a dab of rouge onto the child's nose. Before about fifteen months, a baby smiles at the mirror, pats it and treats the image as a playmate. Between eighteen months and two years, most children reach for their own nose. That is also about the age they begin to use the words me and mine and to show embarrassment.
AdvertisementTry thisWith a toddler in the family, try the rouge test using a dab of lipstick on the nose during an ordinary face wipe. A child under fifteen months pats the mirror. A two-year-old touches the nose and often looks at you in surprise. -
The surprises
3. Dolphins, elephants and magpies
Has your pet done this?For three decades the list ended with apes. Then, in 2001, two bottlenose dolphins at the New York Aquarium were marked with temporary ink on parts of their bodies they could not see. Each swam directly to a mirror and twisted and turned to expose the marked spot. Dolphins have no hands to touch a mark, so the researchers judged them by how they positioned themselves to look.
AdvertisementIn 2006, three Asian elephants at the Bronx Zoo were given a mirror eight feet square. One of them, a female named Happy, repeatedly touched a white X painted on her forehead with the tip of her trunk while standing at the mirror. She ignored an invisible mark on the other side of her head. The other two elephants did not pass.
AdvertisementIn 2008 came the first bird. European magpies, members of the crow family, were given a small colored sticker on the throat, below the beak, where they could see it only in a mirror. Some of the birds scratched at it with a foot until it came off. With a black sticker that vanished against their black feathers, they did nothing.
Try thisNotice what these animals share. Apes, dolphins, elephants and crows are all long-lived, large-brained and intensely social. The next time you watch crows or magpies in your yard, you are looking at some of the sharpest minds outside the primates.Advertisement -
The argument
4. A small fish joins the list
Has your pet done this?In 2019 a Japanese research team reported that the cleaner wrasse had passed the mark test. This is a finger-length reef fish that makes its living picking parasites off larger fish. It was the first fish to do so, and the claim set off one of the liveliest arguments in animal behavior.
The wrasse were given a mirror in their tanks. Like the chimps, they first attacked the reflection, then stopped, then began behaving oddly in front of it, swimming upside down and dashing toward the glass. The researchers then injected a small brown mark under the skin of the throat. Fish with a mirror turned to view the throat, then scraped it against the sand or a rock. Fish with a clear mark, or with no mirror, did not.
AdvertisementCritics, Gallup among them, point out that a brown spot looks like a parasite, and that removing parasites is what a cleaner wrasse does by instinct. The fish may see a spot on a fish and react, without any idea of self. The Japanese team has answered with larger studies, including work showing the fish respond to photographs of their own faces.
AdvertisementEither a small fish has a sense of self, or the famous test does not measure what we thought it did.
Try thisTreat this one as an open question, because the scientists do. Both possible answers are interesting, and it is a good subject to raise the next time someone at the table says fish do not think. -
The majority
5. A stranger in the glass
Has your pet done this?Most animals never get past the first stage. They see another animal and respond as their species responds to a stranger. A Siamese fighting fish flares its gills and fins. A leopard growls and circles behind the mirror to find the intruder. Monkeys threaten. Parakeets treat the mirror as a companion and will court it and feed it for years.
AdvertisementThe case most people meet at home is the bird at the window. In spring and early summer, male northern cardinals, American robins, mockingbirds, bluebirds and towhees defend a nesting territory against rivals of their own kind. When one catches sight of himself in a window, a car mirror or a shiny hubcap, he sees a rival that will not back down. He attacks, the rival attacks back, and the fight goes on for hours a day, sometimes for weeks. Wild turkeys do the same to parked cars and can scratch the paint.
AdvertisementThe bird is rarely hurt, but it wastes energy it needs for raising young. This is different from a bird striking a window in flight, which happens because it does not see the glass at all.
Try thisRemove the reflection from the outside. Slip a sock or a plastic bag over each car mirror when parked, and cover the outside of the window with a screen, netting or a streaked film of soap for two or three weeks. Closing the curtains inside does not help.Advertisement -
Dogs
6. They use their nose instead
Has your pet done this?Dogs fail the mirror test. A puppy meeting its first mirror will bark, bow and try to play, then look behind the frame. Within days or weeks it loses interest, and most adult dogs walk past a mirror without a glance. Dogs can learn to use one, though. Many will spot a person or a treat in the reflection and turn around to find it.
AdvertisementThe failure says more about the test than about the dog. A dog's world is built from scent. Its nose is thousands of times more sensitive than ours, and a reflection that smells of nothing barely counts as real.
So researchers tried a version that suits the animal. One biologist in Colorado spent five winters moving patches of urine-marked snow and timing his own dog's reactions. The dog gave his own marks only a passing sniff and lingered over those of other dogs. In a later laboratory study, pet dogs were offered canisters containing their own urine, and their own urine with another scent added. They spent much longer investigating their own smell when it had been changed, the scent equivalent of noticing a mark on your face.
AdvertisementTry thisOn your next walk, watch how your dog treats a spot it marked earlier compared with one left by another dog. It will pass over its own quickly and study the stranger's at length. Your dog knows which is which. -
Cats
7. Mostly unimpressed
Has your pet done this?Cats do not pass the mark test either. A kitten seeing a mirror for the first time often arches its back, fluffs its tail and approaches sideways, or bats at the glass and peers around the edge. That phase is short. The image does not smell like a cat, does not sound like one and never does anything new, so most cats file it under things that do not matter. An adult cat usually walks past a mirror as if it were a wall.
AdvertisementA few cats never settle and go on hissing or attacking. That is most common in cats that are anxious or have had little contact with other cats, and it can flare up when a mirror appears in a new place.
Like dogs, cats rely on other senses to tell who is who. They know their own scent, which they spread by rubbing their cheeks on furniture and on you. They recognize their names and the voices of their owners. Many also learn to use a mirror as a tool, watching you in the glass and turning to face you when you move.
AdvertisementTry thisIf your cat is upset by a mirror, do not force the meeting. Cover the lower part of the glass with paper or frosted film for a few weeks, then uncover it a little at a time while offering treats nearby. -
The doubts
8. What the test misses
Has your pet done this?The mark test is elegant, but it has real weaknesses, and researchers argue about them openly. The first is that it is a test for visual animals. It suits apes and people, who inspect themselves and each other by eye. It is poorly matched to a dog, a mole or a bat.
AdvertisementThe second is motivation. To pass, an animal must care about a spot on its skin. Apes groom constantly, so they do. An elephant spends its days coated in mud and dust, and a mark on its forehead may simply not be worth investigating. Failing can mean not bothered.
The third is that the result is treated as all or nothing. Rhesus monkeys fail the standard test, yet after weeks of training they learn to use mirrors to examine themselves. Children in cultures where toddlers seldom see mirrors often freeze instead of touching the mark, although they are developing normally. Many scientists now see self-awareness as a matter of degree. Every animal must tell its own body from the rest of the world in order to move, eat and avoid biting itself.
AdvertisementFailing the mirror test may only mean that vision is not how an animal understands the world.
Try thisWhen you watch an animal meet a mirror, look past pass or fail. Does it check behind the glass, test the image by moving, or lose interest? Each of those is the animal working something out.
The short version
Only a handful of species recognize themselves in a mirror: chimpanzees, bonobos, orangutans, some gorillas, bottlenose dolphins, at least one Asian elephant, European magpies and, more controversially, a small reef fish. Human children join them at about eighteen months to two years. For nearly every other animal, a reflection is a rival, a puzzle or nothing at all.
That tells us less about how clever an animal is than about which senses matter most to it. Your dog knows itself by smell, and your cat has decided the mirror is not worth its attention. Neither is missing anything it needs.
As for the cardinal at the window, he is not confused about who he is. He is defending his home against the most stubborn rival he has ever met. Cover the glass for a few weeks, and he will get back to the business of spring.
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