New Caledonian crows’ responses to mirrors F. S. Medina * , A. H. Taylor, G. R. Hunt, R. D. Gray * Department of Psychology, University of Auckland article info Article history: Received 15 November 2010 Initial acceptance 28 January 2011 Final acceptance 22 July 2011 Available online xxx MS. number: 10-00804 Keywords: Corvus moneduloides mirror image stimulation mirror-mediated spatial location mirror use New Caledonian crow social behaviour Recent mirror studies with two corvid species have reported contrasting findings. Jungle crows, Corvus macrorhynchos, showed no self-contingent behaviour when confronted with mirrors, whereas Eurasian magpies, Pica pica, reportedly passed the ‘mark’ test for self-recognition. We investigated mirror-induced behaviour in wild-caught New Caledonian crows, Corvus moneduloides. We first documented the response of 10 naïve crows to a 50 Â 40 cm vertical mirror. The crows responded to their mirror image with social displays and engaged in search and mirror-directed exploratory behaviour. Their agonistic social displays towards the mirror did not decrease in frequency over time. We then gave two of these crows and two naïve ones a mirror-mediated spatial location task with a horizontal mirror. All four crows successfully used the horizontal mirror to locate hidden food. Therefore, they were able to exploit the correlation between an object’s mirror reflection and its location in the real world. This suggests that New Caledonian crows may also have the ability to develop an understanding of how mirrors represent objects in the environment, despite the lack of self-directed behaviour in front of mirrors. Our study fills an important gap in mirror studies on corvids, which are considered to be the primate equivalents of the avian world. Ó 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Mirror image stimulation (MIS) has become a standard test in comparative animal psychology ever since Gallup (1970) conducted the first objective ‘mark’ test for mirror self-recognition. In the mark test, animals have to touch marks (e.g. coloured dots) on their bodies that are only visible in a mirror. In this article, we use the term mirror self-recognition (MSR) to define the objective behav- iour an animal performs when passing such mark tests (i.e. animals that touch the mark in front of a mirror have MSR). Originally, however, this test was specifically designed to test the long-held view in primatology that chimpanzees, Pan troglodytes, ‘realised that their behaviour was the source of the behaviour being seen in the mirror’ (Gallup & Povinelli 1993, page 327). In spite of the ongoing debate on whether animals that show MSR possess human-like self-awareness (Gallup & Povinelli 1993; Mitchell 1993a, b, 1995, 1997a; Heyes 1994, 1995, 1996; Gallup et al. 1995; Swartz 1997; Bard et al. 2006), mirror-induced responses in animals continue to be reported. Such reports range from animals that continuously exhibit species-specific social behaviours to those that spontaneously engage in self-exploratory behaviour in front of mirrors (Pepperberg et al. 1995; Reiss & Marino 2001; Gallup et al. 2002; de Waal et al. 2005; Reznikova 2007). Until recently, animals other than the great apes were thought to view mirror images only as conspecifics (Gallup 1970; Kusayama et al. 2000). Nonprimates now reported to pass the mark test are one bottlenose dolphin, Tursiops truncatus (Reiss & Marino 2001), one Asian elephant, Elephas maximus (Plotnik et al. 2006) and two Eurasian magpies, Pica pica (Prior et al. 2008). Animals that cannot be tested or do not conclusively pass the mark test nevertheless show other interesting, but less controversial, intermediate mirror-induced responses (Gallup 1970; Povinelli 1989; Pepperberg et al. 1995; de Waal et al. 2005). For example, mirror-triggered search is a basic task in which animals in the presence of mirrors search for hidden food (visible in the mirror) that is placed in fixed, familiar places (Menzel et al. 1985; Anderson 1986; Povinelli 1989). As food is always hidden in the same location, subjects may use the mirror only as a cue to start searching rather than to obtain information of the food’s precise whereabouts (Povinelli 1989; Pepperberg et al. 1995). In contrast, in the mirror-mediated object discrimination task (Menzel et al. 1985; Pepperberg et al. 1995) subjects are required to look at mirror images of hidden objects that are either aversive or rewarding. They must then consistently choose to move towards them or move away from them. Animals can do this by exploiting the correlation between an object and its reflection, but they do not need to * Correspondence: F. S. Medina and R. D. Gray, Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. E-mail addresses: fmedinaro@gmail.com (F. S. Medina), rd.gray@auckland.ac.nz (R. D. Gray). Contents lists available at ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav 0003-3472/$38.00 Ó 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.anbehav.2011.07.033 Animal Behaviour xxx (2011) 1e13 Please cite this article in press as: Medina, F. S., et al., New Caledonian crows’ responses to mirrors, Animal Behaviour (2011), doi:10.1016/ j.anbehav.2011.07.033