Investigation of Mirror-Self Recognition in Ravens (Corvus corax)

Large-brained birds, such as corvids and parrots, tend to fail tests for self-recognition (mirror self-recognition [MSR]), but the limited positive evidence for MSR in these species has been questioned due to methodological limitations. In the present study, we aimed to investigate MSR in ravens by performing three mirror tests: a mirror exposure test, a mirror preference test, and a mark test. Across all three tests, the ravens' behavior was not consistent with MSR. Three out of six ravens infrequently interacted with the mirror and the nonmirror surfaces. Two birds explored the mirror and occasionally displayed contingent behaviors. Finally, the ravens made very few social displays toward the mirror, suggesting that at this stage they did not treat their reflection as a conspecific. These findings, along with the current evidence available, raise further questions on the validity of relying on one test to establish self-recognition and call for the development of methods beyond mirror tests to explore self-recognition in nonhuman animals.