Photoperiodism, melatonin and the pineal: it's only a question of time.
D000818:Animals; D001717:Birds; D003624:Darkness; D005260:Female; D008027:Light; D008297:Male; D008550:Melatonin / Q000502:physiology*; D010507:Periodicity; D010870:Pineal Gland / Q000502:physiology*; D012621:Seasons; D012726:Sexual Behavior, Animal
D008550:Melatonin