‘Fixed direction’-responses of birds in the geomagnetic field

Figures & data

Figure 1 ‘Fixed direction’-responses observed in migratory birds. The arrows mark the mean vectors based on the individual mean headings of 10 or 12 birds; the symbols at the periphery of the circle mark the mean ‘fixed direction’ in Australian silvereyes (diamonds) and European robins (triangles). The wavelengths of the monochromatic or bichromatic lights are indicated; for the respective intensities, see text (reviewed in refs. 2, 4 and 6–9).

Table 1 Differences between compass orientation and fixed direction responses in birds

	Compass orientation	‘Fixed direction’-responses
Nature of response	axial → inclination compass	polar
Light-dependency	requires short-wavelength light	occur also in total darkness
Effect of oscillating fields	disorientation	no effect
Anesthesia of the upper beak	no effect	disorientation
Underlying physical process	radical pair mechanism	magnetite-based mechanism
Site of receptors	right eye	skin of upper beak
Nerve mediating information	optical nerve	branch of trigeminal nerve
Directions preferred	any: migratory direction, home direction	one specific direction only,
	or acquired directions	depending on the light regime

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