New Caledonian crows’ responses to mirrors

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 × 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.

► Mirror-induced behaviour in wild-caught, tool-using New Caledonian crows.
► No self-contingent behaviour in front of vertical mirrors after short exposure.
► Successful use of a horizontal mirror to locate cached food.
► Corvus species are capable of primate-like use of mirror information.
► Longer mirror exposure needed to test for self-contingent behaviour.