Avian Navigation System
The avian navigation system is rather complex, based on many factors, and it even used two aspects of the magnetic field. If, in a given situation, one can show that the receptors in the beak have no effect, that does not mean that they do not have one in another situation!
Anaesthesia of the upper beak normally does not cause disorientation. If we test migratory robins that use their magnetic compass, anaesthesia of the beak has no effect (see attached paper in J. R. Soc. Interface 7), because the compass is based on radical pair processes in the eye, which are not affected by anaesthesia of the beak. (see the Peter Hore’s article: the Quantum Robin – Editor)
If, however, the magnetic compass is disrupted by certain light regimes like in the case of the paper in J. Exp. Biol mentioned below, the receptors in the beak take over, and then – and only then – anaesthesia of the beak causes disorientation. In pigeons who use information from the receptors in the beak as a component of their map, local anaesthesia of the beak does not lead to disorientation either, because at most sites, they can rely on other cues.
In birds, there are two magnetoreceptors: one in the eye to provide information on directions, and one in the skin of the upper beak that appears to normally provide information on intensity (see Wiltschko et al. 2010, Curr. Biol20 and Schiffner et al. 2011 , Naturwissenschaften 97; these two articles are attached), but under certain circumstances can also provide directing information (see paper in J. Exp. Biol. mentioned below). I know that years ago Peter Semm recorded responses to magnetic changes in the pineal, but unfortanately, he gave that up in favor of the visual system. Amphibians, however, seem to have their magnetic compass in the pineal, as shown by John Phillips and Mark Deutschlander.
Roswitha Wiltschko
wiltschko@bio.uni-frankfurt.de
Magnetic Compass of Birds Is Based on a Molecule with Optimal Directional Sensitivity
Tracking Pigeons in a Magnetic Anomaly and in Magnetically ‘Quiet’ Terrain
Tracking pigeons in a magnetic anomaly and in magnetically “quiet” terrain
The Role of the Magnetite-Based Receptors in the Beak in Pigeon Homing
The Role of the Magnetite-Based Receptors in the Beak in Pigeon Homing
Directional orientation of birds by the magnetic field under different light conditions
Magnetic compass of birds is based on a molecule with optimal directional sensitivity