Olfactory navigation in homing pigeons: the last challenge.

The olfactory navigation hypothesis of pigeon homing was recently challenged by the discovery in the upper beak of putative magnetoreceptors innervated by the ophthalmic branch of the trigeminal nerve. To assess whether the nature of the cues used for navigation is determined by the kind of stimuli to which the birds are preferentially exposed during development, we tested the navigational performance of pigeons subjected when young to section of either the ophthalmic branch of the trigeminal nerve (V1) or the olfactory nerve and then subjected to training flights after the surgery. Section of V1 had no effect on homing performance, but olfactory cues are needed for development of the navigational map.