Bottlenose dolphin’s mirror self-recognition

By Silje Caroline Bjørkdahl

The bottlenose dolphins (Tursiops truncatus) have similarities to humans, for instance that they communicate with each other in their own language, which consists of squeaks, whistles and body language. They communicate in order to keep in track with their pod and to warn each other about dangers. They are well known as good friends to humans. There has been observed rescues of divers by dolphins, and they swim among humans if they see them, without doing any harm. Since the 1970 until today, studies on their mental representatives have been done. Such as acoustic- and behaviour-mimicry, finding the categorization, presence and matching of an object, behaviour between animals and mirror self-recognition behaviour.

I think that this last mentioned study is very interesting; that animals so taxonomically distant from us, have the same ability to recognise themselves in a mirror. Therefore I have chosen to write about the study: “Bottlenose dolphin’s mirror self-recognition”.

Prior to this study 7-8 years ago, the only species known to have the ability to recognise itself in a mirror were humans and great apes. Today we also know that elephants and possibly pigeons have the same ability. The test that should be passed to be a “self-recognizer” is to determine whether the individual can recognize it self in a mirror. The researchers therefore marked or pretended to mark the dolphins’ bodies, to see if the dolphins would give this any attention.

The dolphins used in this study were; two captive born, 17- and 13-year-old males. They lived together in the pools of the New York Aquarium, where the studies took place. The study was in different pools, with different surfaces of varying degrees of reflectivity. The dolphins were videotaped, so the observers could study the behavior without interfering. They looked for social, ambiguous, non-directed or self-recognizing behaviors.

The researchers’ hypothesis is that the dolphins should not show any social behavior to the mirror, but they should spend more time in front of it after a marking or pretend-marking. They also should be looking for a mirror shortly after the marking process. This is three qualifications that an animal should achieve to be a “self-recognizer”.

These three predictions were achieved; the dolphins didn’t show any social behavior in the mirrors, not even after the mirrors where taken away from the pool and put back again. They also used more time by the mirror, and they swam to a mirror shortly after they were marked, or pretended to be marked.

After a pretend marking the dolphin investigated himself in the mirror, to look for the marking he thought had been given. When he couldn’t find the mark he swam away from the reflecting surface. The dolphins also showed that they looked for the best reflecting surfaces in the pools after they had been marked, or thought they had been marked.

There was one time one of the dolphins that was marked on his tongue, the first thing he did after the marking was to swim as fast as he could to a mirror, and he opened his mouth to look at the mark.

Another observation was that the dolphins didn’t pay any attention to the other dolphin’s mark, unlike the chimpanzees. This is probably because of that the dolphins don’t groom each other like the primates do.

These results and findings proof that the dolphins are able to recognize themselves in a mirror, and to investigate their own body. Since other animals, as for instance the gorillas, consider eye contact as an aggressive gesture, they didn’t pass the mirror self-recognition test. Dogs, cats and 1 year old humans can show fear, curiosity or ignore a mirror while birds attack it. The dolphins don’t show any signs of this non-self-recognition behaviour. I think that this is a proof for that the dolphins have the ability to mirror self-recognition.

I also think that their good sight, both under water and in air, can be one of the reasons that they can see themselves in a mirror. The dogs, for instance, may be unable to self-recognition because of their red/green sight and poor visual determination.

References:

Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=33317

Bottlenose dolphin:

http://en.wikipedia.org/wiki/Bottlenose_dolphin

Mirror test:

http://en.wikipedia.org/wiki/Mirror_test