Homoiothermy is the maintenance by an animal in which body temperature remains constant and does not change with the change of environmental temperature. 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: 36-38ºC in mammals and 38-40ºC 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.