448-459<span style="mso-fareast-font-family:TimesNewRomanPSMT;
mso-ansi-language:EN-IN">Animals in the wild are exposed to daily variations in
sun light, viz. duration, intensity and spectrum. Photosensitive blackheaded
buntings (Emberiza melanocephala) were exposed to photoperiods
differing in the length of light period, wavelengths and intensity. The effects
of such light changes were measured on locomotor activity rhythm as well as
seasonal responses like development of migratory restlessness: Zugunruhe,
body mass and gonadal growth. The results show that the buntings are
differentially responsive to light wavelengths and intensities and are
indicative of a
phase-dependent action of light on the circadian photoperiodic system. These
birds seem to use changes in the light variables of the solar environment to
regulate their circadian and seasonal responses.
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