“Most researchers in the field agree that the compass sense is likely seated in cryptochromes within the eye, and many are convinced that there is another sense, most likely a signpost sense, passed through the trigeminal nerve and probably based on some sort of iron-containing, magnetism-sensing cells in beaks or snouts. Then there is [David] Dickman and [Le-Qing] Wu’s idea: that both of these abilities may rely on receptors in the inner ear.”