a method of cooling, used by many mammals, most birds, and some reptiles, accomplished by means of the evaporation of water from internal body (body heat) surfaces. As the animal's body temperature rises, its respiration rate increases sharply; cooling results from the evaporation of water in the nasal passages, mouth, lungs, and (in birds) air sacs. Like other forms of evaporative cooling (e.g., perspiration), panting expends large amounts of water, which must be replaced if the animal is to maintain effective heat regulation.