An attempt to develop an operant conditioning paradigm to test for magnetic discrimination behavior in a migratory songbird

Abstract

Birds are thought to possess two magnetosensory systems: (1) a chemical sensor in the bird’s eye, and (2) a magnetoreceptor innervated by the ophthalmic branch of the trigeminal nerve (V1) and presumably located in the upper beak. It has been recently demonstrated that the visually mediated magnetosensory system is crucial to the magnetic compass of the European Robin (Erithacus rubecula). In contrast, the trigeminal nerve system, despite neuronal responses to magnetic stimuli, is neither necessary nor sufficient for magnetic compass orientation in this species. Unfortunately, the potential role of the trigeminal organ is unlikely to be elucidated by the classical behavioral paradigm of the orientation cage, because it tests only for spontaneous compass responses. An operant conditioning study by Mora et al. (Nature 432:508–511, 2004) demonstrated that Homing Pigeons can be conditioned to discriminate the presence and absence of a strong gradient magnetic field stimulus. This discrimination depended on intact ophthalmic branches of the trigeminal nerves. Here, we report detailed attempts aimed at adapting the behavioral paradigm used by the above study for a model migratory bird, the European Robin. We tested three variants of a conditioning procedure very similar to that of Mora et al. (Nature 432:508–511, 2004). Despite extensive training, we were not able to demonstrate that our experimental birds were able to discriminate the magnetic stimuli presented to them. This was, however, not due to a general unsuitability of the conditioning setup for this species, because the robins were able to successfully discriminate the presence and absence of an auditory stimulus in the same setup.