(d) : Homoiothermy is the maintenance by an animal of its internal body temperature at a relatively constant value by using metabolic processes to counteract fluctuations in the temperature of the environment. Homoiothermy occurs in birds and mammals, which are described as endotherms. The heat produced by their tissue metabolism and the heat lost to the environment are balanced by various means to keep body temperature constant: 36-38°C in mammals and 38-40°C in birds. The hypothalamus in the brain monitors blood temperature and controls thermoregulation by both nervous and hormonal means. Thus parrot (bird) and platypus and kangaroo (mammals) are homoiothermic animals.