Clocks, pineals and compasses.
D000818:Animals; D001683:Biological Clocks; D001717:Birds / Q000502:physiology*; D008550:Melatonin / Q000502:physiology; D009949:Orientation / Q000502:physiology; D010870:Pineal Gland / Q000502:physiology*
D008550:Melatonin