Table 1.

Proposed mechanisms of magnetoreception in birds.

mechanism	location	function	innervation	brain region	diagnostic
radical-pair chemical photoreceptor	eye	inclination (compass)	not known	cluster Na,b	MHz oscillating magnetic fieldsc
sensory cells containing iron minerals	beakd	intensity (for map?)e	trigeminal nerve (ramus ophthalmicus medius, ROM)d	not known	magnetic pulse,f conditioning to intensity anomaly and lesions of ROMe
sensory cells containing iron minerals	beak	polarity (compass?)	trigeminal nerve	not known	field reversal combined with local anaesthesia of beakg

^aMouritsen et al. (2005).

^bZapka et al. (2009).

^cRitz et al. (2004).

^dFleissner et al. (2003).

^eMora et al. (2004).

^fWiltschko et al. (1994).

^gWiltschko et al. (2005).