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. 2017 May 16;12(5):e0176717.
doi: 10.1371/journal.pone.0176717. eCollection 2017.

Are horses capable of mirror self-recognition? A pilot study

Paolo Baragli  1   2 , Elisa Demuru  2 , Chiara Scopa  1   2 , Elisabetta Palagi  2   3
Affiliations

Are horses capable of mirror self-recognition? A pilot study

Paolo Baragli et al. PLoS One. .

Abstract

Mirror Self-Recognition (MSR) unveils complex cognitive, social and emotional skills and it has been found only in humans and few other species, such as great apes, dolphins, elephants and magpies. In this pilot study, we tested if horses show the capacity of MSR. Four subjects living socially under naturalistic conditions were selected for the experiment. We adopted the classical mark test, which consists in placing a coloured mark on an out-of-view body part, visible only through mirror inspection. If the animal considers the image as its own, it will use its reflection to detect the mark and will try to explore it. We enhanced the classical paradigm by introducing a double-check control. Only in the presence of the reflecting surface, animals performed tactile and olfactory exploration of the mirror and looked behind it. These behaviors suggest that subjects were trying to associate multiple sensory cues (visual, tactile and olfactory) to the image in the mirror. The lack of correspondence between the collected stimuli in front of the mirror and the response to the colored mark lead us to affirm that horses are able to perceive that the reflected image is incongruent when compared with the memorized information of a real horse. However, without replication of data, the self-directed behavior towards the colored marks showed by our horses cannot be sufficient per se to affirm that horses are capable of self-recognition.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Detailed description of the testing area.
A: the area of the L-shaped enclosure in which mirror was positioned; B: the other part of the L-shaped enclosure; f: the short fence delimiting the A and B areas; xf: the thick fence added to prevent the fellow horse looked at the mirror by leaning over the fence.
Fig 2
Fig 2. Shape, color and position of the sham and colored marks during the Sham and Mark test.
Day 4 (SHAM control): both cheeks of the horse were painted with the sham mark (basal control for tactile cues) (A and C). Day 5 (MARK test 1): the left cheek was painted with colored mark (B and D, yellow for Julia and Calippo, blue for Betsie and Gina) while right cheek was painted with sham mark (C). Day 6 (MARK test 2): the position of sham and colored marks was inverted and, therefore, colored mark was positioned on the right side while sham mark was on the left side. The presence of the sham mark on the opposite cheek of the colored mark (during MARK test 1 and 2), was necessary to avoid the bias due to a tactile stimulation.
Fig 3
Fig 3. Frequency of scraping events directed towards both cheeks.
Bar-graphs showing the frequency of the scraping events (SCRA) that each subject directed towards both sides of their face (see S1 Fig) across the four different conditions when the colored mark was positioned on the left cheek (a) (CM, OM, SHAM, MARK 1; df = 3; Julia: χ2 = 137.05, p < 0.0001; Calippo: χ2 = 5.27, p = 0.1531; Gina: χ2 = 58.61, p < 0.0001; Betsie: χ2 = 34.68, p < 0.0001) and when it was placed on the right cheek (b) (CM, OM, SHAM, MARK 2; df = 3; Julia: χ2 = 27, p < 0.0001; Calippo: χ2 = 10.62, p = 0.014; Gina: χ2 = 28.85, p < 0.0001; Betsie: χ2 = 42, p < 0.0001).
Fig 4
Fig 4. Frequency of scraping events directed towards the left or the right cheek.
Bar-graphs showing the frequency of the scraping events (SCRA) that each subject directed specifically towards the left side of their face (see S1 Fig) across the four different conditions when the colored mark was placed on the left cheek (a) (CM, OM, SHAM, MARK 1; df = 3; Julia: χ2 = 86.02, p < 0.0001; Calippo: nd—expected values less than 5; Gina: χ2 = 32.52, p < 0.0001; Betsie: nd—expected values less than 5) and when it was placed on the right cheek (b) (CM, OM, SHAM, MARK 2; df = 3; Julia, Calippo, Gina, Betsie: nd—expected values less than 5).
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Grants and funding

The authors received no specific funding for this work.

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