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Self-recognition in corvids: evidence from the mirror-mark test in Indian house crows (Corvus splendens)

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Abstract

The ability to recognize oneself is separate from recognizing a conspecific. Self-recognition is a higher cognitive function and generally tested by a mirror-mark paradigm, in which the individual recognizes and responds to an inconspicuously placed mark on body from its mirror-reflected image. Although initially suggested to be associated with large-brained mammals, the ability of self-recognition has now been shown in non-mammals, including fish and birds. Hence, studies on many more species might be useful to understand general principles and underlying mechanisms of the evolution of social intelligence. Here, we examined self-recognition ability in Indian house crows (Corvus splendens), by testing them first for mirror-induced responses and then for the mark-directed responses. A circular coloured mark was inconspicuously placed on the throat under the bill where crows could see it only from its mirror-reflected image; a similar black mark placed at identical location which was difficult to be seen served as the control condition. We evaluated how closely crows viewed and inspected the object, and expressed social, contingent and self-directed responses to the mirror and cardboard. Crows exhibited greater preference in response to the mark when in front of the mirror, compared to they were in front of the non-reflective black cardboard. The majority (4/6) crows responded to the mirror-reflected self-image, as evidenced by attempts to remove the coloured mark by using beak or claws; no such response was found in control condition. These results suggest self-recognition by Indian house crows, and support the growing evidence that the ability of self-recognition is more widely present among animals.

Zusammenfassung

Selbsterkennung bei Rabenvögeln: Anhaltspunkte aus einem Spiegeltest an Glanzkrähen ( Corvus splendens )

Die Fähigkeit, sich selber zu erkennen, unterscheidet sich vom Erkennen eines Artgenossen. Selbsterkennung ist eine höhere kognitive Funktion und wird üblicherweise mittels einer Spiegel-Versuchsanordnung getestet, bei dem ein Individuum eine unauffällig am Körper platzierte Markierung im Spiegelbild erkennt und auf diese reagiert. Obwohl die Fähigkeit zur Selbsterkennung ursprünglich mit Säugetieren mit großem Gehirn in Verbindung gebracht wurde, konnte sie inzwischen auch bei Nicht-Säugern, darunter Fischen und Vögeln, nachgewiesen werden. Daher könnten Untersuchungen an vielen weiteren Arten hilfreich für das Verständnis der generellen Prinzipien und der zugrundeliegenden Mechanismen der Evolution sozialer Intelligenz sein. Hier untersuchten wir die Fähigkeit zur Selbsterkennung bei Glanzkrähen (Corvus splendens), indem wir zunächst deren Reaktionen auf Spiegel und anschließend ihre Reaktionen auf Markierungen testeten. Ein runder farbiger Punkt wurde an unauffälliger Stelle an der Kehle unter dem Schnabel angebracht, wo die Krähen ihn nur an ihrem Spiegelbild sehen konnten; als Kontrolle diente ein ähnlicher schwarzer, schwer sichtbarer Punkt, der an derselben Stelle angebracht wurde. Wir werteten aus, wie genau die Krähen das Objekt betrachteten und untersuchten; ebenfalls bewerteten wir soziale, zufällige und selbstbezogene Reaktionen auf den Spiegel und die Pappe. Die Krähen reagierten bevorzugt auf den Punkt, wenn sie sich vor dem Spiegel befanden, verglichen mit einer nicht-reflektierenden schwarzen Pappe. Die Mehrzahl der Krähen (4/6) reagierten auf ihr Spiegelbild, wie an ihren Versuchen zu erkennen war, den farbigen Punkt mit Schnabel oder Krallen zu entfernen; diese Reaktion zeigten sie unter Kontrollbedingungen nicht. Diese Ergebnisse sprechen für Selbsterkennung bei Glanzkrähen und unterstützen die zunehmenden Hinweise darauf, dass die Fähigkeit zur Selbsterkennung bei Tieren weiter verbreitet ist.

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Funding

This study was supported by research grants from DST-DU PURSE program to VK. The facility used was built under the grant support to VK from the Department of Science and Technology under its Cognitive Science Initiative Program.

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Correspondence to Vinod Kumar.

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The authors declare no conflict of interest.

Ethical approval

This study was conducted on adult Indian house crows procured from the wild. The procurement of animals from the wild was in full compliance with permission and guidelines of the office of Chief Wildlife Warden, New Delhi (Permit No. F.WLI/111/08/CWLW/383). All institutional guidelines for the care and use of animals were followed. All the experimental procedures were approved by the Institutional Animal Ethics Committee of the University of Delhi, India (Protocol # DU/ZOOL/IAEC-R/2018/08).

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Communicated by F. Bairlein.

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Video S1. Mirror image exploration: Time-lapse video of the duration that crow spent in viewing while in front of the mirror. The individual tries to observe mirror reflection from a close distance. Note: inspection of individual’s own mirror image

Video S2. Social behaviour in mirror exploration sessions: Repeated approach (aggression) of crow to its mirror image. Note: jump towards mirror image in frontal position with claws up

Video S3. Contingent behaviours in the mirror exploration session: Crow moves back-and-forth towards mirror, testing for contingencies between own body and image of the self

Video S4. Head shake behaviour from the mirror mark test

Video S5. Plumage ruffling observed during mirror exploration sessions

Video S6. Body directed behaviour (preening) in the mirror mark (M–M) test: Crow tries to preen wing and flank areas. Notice it stops and observes the mirror image (at 4th second) before it resumes the preening. The yellow mark can be seen at 12th second in the mirror image

Video S7. Mirror preference: The sequence of looking (peeking) behind the mirror

Video S8. Mark-directed response using beak: In the mirror mark (M–M) test, a crow observes mirror image, recognizes it as of the self and attempts at removing yellow coloured mark (visible at 9th second in video clip) using beak

Video S9. Mark-directed response using foot: In the mirror mark (M–M) test, a crow observes mirror image, recognizes it as of the self and attempts at removing red coloured mark (visible at 9th second in video clip) using left foot. After a brief pause, the crow uses right foot for the same

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Buniyaadi, A., Taufique, S.K.T. & Kumar, V. Self-recognition in corvids: evidence from the mirror-mark test in Indian house crows (Corvus splendens). J Ornithol 161, 341–350 (2020). https://doi.org/10.1007/s10336-019-01730-2

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