title: Magnetoreception in birds: no intensity window in "fixed direction" responses.
abstract: Under 502 nm turquoise light combined with 590 nm yellow light and in total darkness, European robins, Erithacus rubecula, no longer prefer their migratory direction, but exhibit so-called fixed direction responses that do not show the seasonal change between spring and autumn. We tested robins under these light conditions in the local geomagnetic field of 46 microT, a field of twice this intensity, 92 microT, and a field of three times this intensity, 138 microT. Under all three magnetic conditions, the birds preferred the same easterly direction under turquoise-and-yellow light and the same northwesterly direction under dark, while they were oriented in their seasonally appropriate direction under control conditions. "Fixed direction" responses are thus not limited to a narrow intensity window as has been found for normal compass orientation. This can be attributed to their origin in the magnetite-based receptor in the upper beak, which operates according to fundamentally different principles than the radical pair mechanism in the retina mediating compass orientation. "Fixed direction" responses are possibly a relict of a receptor mechanism that changed its function, now mainly providing information on magnetic intensity.
authors.affiliation: FB Biowissenschaften, J.W. Goethe-Universität Frankfurt, Siesmayerstrasse 70, 60054, Frankfurt am Main, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wiltschko
authors.forename: Lars
authors.initials: L
authors.lastname: Dehe
authors.forename: Katrin
authors.initials: K
authors.lastname: Stapput
authors.forename: Peter
authors.initials: P
authors.lastname: Thalau
authors.forename: Roswitha
authors.initials: R
authors.lastname: Wiltschko
mesh_terms: D025041:Animal Migration; D000818:Animals; D000836:Animals, Zoo / Q000502:physiology; D055253:Color Vision / Q000502:physiology; D003624:Darkness; D004574:Electromagnetic Fields; D005858:Germany; D008027:Light; D008029:Lighting; D008280:Magnetics; D009949:Orientation / Q000502:physiology*; D017440:Photoperiod; D012621:Seasons; D020308:Songbirds / Q000502:physiology*