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