 Nocturnal animals have higher body temperatures, greater activity, rising serotonin, and diminishing cortisol during the night—the inverse of diurnal animals.Nocturnal and diurnal animals "both" have increased electrical activity in the suprachiasmatic nucleus, and corresponding secretion of melatonin from the pineal gland, at night.Nocturnal mammals, which tend to stay awake at night, have higher melatonin at night just like diurnal mammals do.