Virtually everyone has wondered which animals are conscious. Post-graduate student Josh Plotnik and his colleagues have just extended the list of candidates to the elephant. Or, more precisely, to an elephant.

Part of the problem with studying consciousness is measuring it. One method is to test for `mirror self-recognition' (MSR), where an animal is marked on a part of its body it cannot see and is then put in front of a mirror. If the animal shows interest in the mark on its own body, then scientists assume that the animal recognises itself in the mirror. MSR is seen only in the hominoids(humans and apes), and possibly in dolphins. MSR may be related to the existence of empathy – the ability to understand another's feelings– since human children develop these two abilities more or less simultaneously. Plotnik and his collaborators, Frans de Waal and Diana Reiss,therefore decided to test for MSR in the elephant, which is reputed to be highly empathetic.

Three female Asian elephants at New York's Bronx Zoo – Happy, Maxine and Patty, all in their 30s – had a jumbo-sized mirror placed in their enclosure. Video recordings revealed behaviours not seen in the mirror's absence: the elephants did not show aggressive or social behaviours to their reflection, but would instead bring food to eat in front of the mirror, or would inspect parts of their body with their trunk. These behaviours suggested that they realised the elephant in the mirror was themselves.

In the final phase of the experiment, to try and test more conclusively for MSR, each elephant was marked with a cross above each eye. One cross was painted with white pigment, the other with a compound that was chemically identical, except that it was invisible. The mirror was then uncovered, and each animal's behaviour observed.

A striking movie published as an on-line supplement to the article shows one of the elephants – Happy – standing in front of the mirror and repeatedly touching the visible mark with her trunk. In fact, Happy touched her face significantly more often during the mark test than in other phases of the experiment. Furthermore, Happy tried to touch only the visible mark, not the invisible control cross above her other eye. The authors conclude that Happy showed MSR, during this experiment at least. However, neither Maxine nor Patty displayed a similar ability, although they showed what appeared to be self-directed behaviour in front of the mirror. When all three were tested again on two subsequent occasions, none of the elephants touched the marks,and were not considered to show MSR.

The authors argue that the fact that all the elephants were interested in the mirror strongly suggests they do have the capacity for self-awareness, but that this particular test may not be an appropriate measure of MSR. This is because elephants regularly cover themselves with dust, changing their appearance. A small cross on their brow might be irrelevant to them. Also,it's possible that not all individuals are self-aware.

This study highlights that while evidence from single individuals is striking, it can also be ambiguous. Happy's behaviour could have been a statistical freak, but the data, and the accompanying movie, are very impressive. It is extremely difficult not to get the very strong impression that she is, indeed, studying her face, using her reflection as a guide. Happy challenges our preconceptions about animal behaviour and should encourage researchers to investigate MSR further in both elephants and other animals. Hominoids may not be as unique as we like to think.

Plotnik, J. M., de Waal, F. B. M. and Reiss, D.(
). Self-recognition in an Asian elephant.
Proc. Natl. Acad. Sci. USA