300
Wolfgang Wiltschko and Roswitha Wiltschko
Behavioral studies aimed at analyzing a possible wavelength dependence of
magnetoreception. Salamanders and birds were tested under nearly monochromatic light of various wavelengths, using oriented behavior as an indicator of
whether or not the test animals could obtain directional information from the
magnetic field in the test situation. Parallels, but also differences, between the two
groups became apparent (Fig. 6).
Shoreward-oriented salamanders using their inclination compass showed normal
orientation when tested under 400 nm violet and 450 nm blue light. A small range
of disorientation followed, and from 500 nm blue-green to 600 nm orange, the
salamanders shifted their orientation by about 90° counterclockwise with respect
to the direction they preferred under white control light (Phillips and Borland
1992b ). Salamanders that had been exposed for a certain period of time to only
long wavelengths of 500 nm and beyond showed a corresponding clockwise shift
when tested under white light. These data suggest that the directional deflection
was caused by salamanders receiving a different type of directional information
under long-wavelength light. Recent findings based on this response suggest the
pineal as the site of magnetoreception (Deutschlander et a!. 1999). For salamanders orienting homeward with their polarity compass, Phillips and Borland (1994)
reported a somewhat different wavelength dependence. Orientation as with white
light was observed only with wavelengths shorter than 400 nm violet; from 450
nm blue to longer wavelengths, the salamanders were no longer oriented.
Discussing the latter finding, the authors point out that the homing behavior they
used as criterion is a combination of navigational processes and compass
orientation; disorientation could also have resulted from an interference with the
navigational step.
A yet different wavelength dependence emerged in birds. Migrants showed
normal migratory orientation from 425 nm to 565 nm, i.e. in the entire blue and
green part of the visual spectrum. Below 588 nm yellow and beyond 630 nm red,
they were disoriented (see Fig. 6). The wavelength range where the magnetic
compass provides birds with correct information is thus much wider than the one
shown in salamanders. Three species of passerine migrants were tested so far (W.
Wiltschko eta!. 1993, W. Wiltschko and R. Wiltschko 1995, 1999, Rappl eta!.
2000).
Homing pigeons (R. Wiltschko and W. Wiltschko 1998) showed similar responses
to the various wavelengths so that this wavelength-dependence may be typical
for a wide variety of birds, if not for all. Magnetic compass orientation in birds
does not depend on the pineal (e.g. Maffei et al. 1983, Schneider eta!. 1994).
While the different responses of shoreward-oriented salamanders to short and
longer wavelengths were indicating an involvement of two antagonistic receptors
(Phillips and Borland 1992b ), the wavelength dependence observed in birds
appeared to resemble an aU-or-none response. Recent experiments, however,
indicate that the situation might be much more complex, as the intensity of the
nearly monochromatic light was also found to affect the birds' behavior. Green
light with a wavelength of 565 nm resulted in excellent orientation in the normal
Wolfgang Wiltschko and Roswitha Wiltschko
Behavioral studies aimed at analyzing a possible wavelength dependence of
magnetoreception. Salamanders and birds were tested under nearly monochromatic light of various wavelengths, using oriented behavior as an indicator of
whether or not the test animals could obtain directional information from the
magnetic field in the test situation. Parallels, but also differences, between the two
groups became apparent (Fig. 6).
Shoreward-oriented salamanders using their inclination compass showed normal
orientation when tested under 400 nm violet and 450 nm blue light. A small range
of disorientation followed, and from 500 nm blue-green to 600 nm orange, the
salamanders shifted their orientation by about 90° counterclockwise with respect
to the direction they preferred under white control light (Phillips and Borland
1992b ). Salamanders that had been exposed for a certain period of time to only
long wavelengths of 500 nm and beyond showed a corresponding clockwise shift
when tested under white light. These data suggest that the directional deflection
was caused by salamanders receiving a different type of directional information
under long-wavelength light. Recent findings based on this response suggest the
pineal as the site of magnetoreception (Deutschlander et a!. 1999). For salamanders orienting homeward with their polarity compass, Phillips and Borland (1994)
reported a somewhat different wavelength dependence. Orientation as with white
light was observed only with wavelengths shorter than 400 nm violet; from 450
nm blue to longer wavelengths, the salamanders were no longer oriented.
Discussing the latter finding, the authors point out that the homing behavior they
used as criterion is a combination of navigational processes and compass
orientation; disorientation could also have resulted from an interference with the
navigational step.
A yet different wavelength dependence emerged in birds. Migrants showed
normal migratory orientation from 425 nm to 565 nm, i.e. in the entire blue and
green part of the visual spectrum. Below 588 nm yellow and beyond 630 nm red,
they were disoriented (see Fig. 6). The wavelength range where the magnetic
compass provides birds with correct information is thus much wider than the one
shown in salamanders. Three species of passerine migrants were tested so far (W.
Wiltschko eta!. 1993, W. Wiltschko and R. Wiltschko 1995, 1999, Rappl eta!.
2000).
Homing pigeons (R. Wiltschko and W. Wiltschko 1998) showed similar responses
to the various wavelengths so that this wavelength-dependence may be typical
for a wide variety of birds, if not for all. Magnetic compass orientation in birds
does not depend on the pineal (e.g. Maffei et al. 1983, Schneider eta!. 1994).
While the different responses of shoreward-oriented salamanders to short and
longer wavelengths were indicating an involvement of two antagonistic receptors
(Phillips and Borland 1992b ), the wavelength dependence observed in birds
appeared to resemble an aU-or-none response. Recent experiments, however,
indicate that the situation might be much more complex, as the intensity of the
nearly monochromatic light was also found to affect the birds' behavior. Green
light with a wavelength of 565 nm resulted in excellent orientation in the normal