Nerves in the beaks of birds may not only serve as a "sixth sense" compass but are also magnetometers capable of measuring the intensity and inclination of the Earth's magnetic field. Researchers at the Goethe University Frankfurt previously studied iron-containing nerve branches in the beaks of homing pigeons. (Note that other scientists propose that cells in bird eyes, not the beaks, act as the primary compass.) Now, neurobiologists Dr. Gerta Fleissner Professor Günther Fleissner report similar structures in robins, garden warblers, and even domestic chickens. From a Goethe University press release (CC-licensed image from Wikipedia):
Specialized iron compounds in the dendrites locally amplify the Earth magnetic field and thus induce a primary receptor potential. Most probably each of these more than 500 dendrites encodes only one direction of the magnetic field. These manifold data are processed to the brain of the bird and here - recomposed - serve as a basis for a magnetic map, which facilitates the spatial orientation. Whether this magnetic map is consulted, strongly depends on the avian species and its current motivation to do so: migratory birds, for example, show magnetic orientation only during their migratory restlessness, as could be shown in multiple behavioural experiments by Prof. Wolfgang Wiltschko, who has discovered magnetic field guided navigation in birds. The cooperation with his research team has suggested that magnetic compass and magnetic map sense are based on different mechanisms and are localized at different sites: The magnetic compass resides in the eye, the magnetometer for the magnetic map lies in the beak."A magnetometer in the upper beak of birds?"