Elsevier

Animal Behaviour

Volume 78, Issue 5, November 2009, Pages 1037-1041
Animal Behaviour

Articles
Pigs learn what a mirror image represents and use it to obtain information

https://doi.org/10.1016/j.anbehav.2009.07.027Get rights and content

Mirror usage has been taken to indicate some degree of awareness in animals. Can pigs, Sus scrofa, obtain information from a mirror? When put in a pen with a mirror in it, young pigs made movements while apparently looking at their image. After 5 h spent with a mirror, the pigs were shown a familiar food bowl, visible in the mirror but hidden behind a solid barrier. Seven out of eight pigs found the food bowl in a mean of 23 s by going away from the mirror and around the barrier. Naïve pigs shown the same looked behind the mirror. The pigs were not locating the food bowl by odour, did not have a preference for the area where the food bowl was and did not go to that area when the food bowl was visible elsewhere. To use information from a mirror and find a food bowl, each pig must have observed features of its surroundings, remembered these and its own actions, deduced relationships among observed and remembered features and acted accordingly. This ability indicates assessment awareness in pigs. The results may have some effects on the design of housing conditions for pigs and may lead to better pig welfare.

Section snippets

Methods

The subjects were 4–8-week-old Large White × Landrace pigs housed prior to and throughout the study on a commercial farm in strawed pens with natural light and food (pig nuts) and water ad libitum. All were familiarized with a red food bowl as a food container. None had seen a mirror, or other reflecting surface, before the studies described here.

The trials took place in a strawed pen (4.6 × 2.8 m) located approximately 30 m away from the home pen. All behaviour was videorecorded. The mirror (0.6 × 

Initial Observations: First Contact with the Mirror

When first encountering the mirror, all seven pigs whose behaviour was recorded in detail walked towards it, sometimes vocalizing, stopped with nose pointing towards the mirror, moved forward again and made contact with the mirror surface with their nose. Some pigs looked behind the mirror after looking at their reflection in it. One female pig, observed during the preliminary study, moved rapidly towards the mirror and broke it, perhaps attacking her mirror image. After initially encountering

Discussion

The aim of this study was to find out whether or not pigs can obtain information from a mirror, as has been demonstrated for humans and other primates, dolphins, elephants, magpies and an African grey parrot, Psittacus erithacus (Pepperberg et al. 1995). The 4–6-week-old pigs studied responded to a mirror initially as if to another pig but later by looking at it as they moved. They moved and then stopped still, apparently looking at their image and its surroundings, oriented either with nose

Acknowledgments

We thank Sophie Prowse for help in caring for pigs, supplying materials and practical guidance, Francisco Bernal for loan of a camera, Gregorio Pesinato for help during experimental trials and the editor and referees for helpful suggestions.

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