A killer whale has a thick layer of body fat, called blubber, that lies underneath its skin. The killer whale's fusiform body shape and reduced limb size, in comparison to land mammals, decreases the amount of surface area exposed to the external environment. Blubber also functions as an energy reserve. In general, cetaceans have a higher metabolic rate than land mammals of similar size. This increased metabolism generates a great deal of body heat.
Mammals lose body heat when they exhale.
Because they breathe less frequently than land mammals, killer whales conserve a considerable amount of heat. A killer whale's circulatory system adjusts to conserve or dissipate body heat and maintain body temperature. Arteries in the flippers, flukes, and dorsal fin are surrounded by veins. Thus, some heat from the blood traveling through the arteries is transferred to the venous blood rather than the environment. A countercurrent heat exchange system in the flippers, flukes, and dorsal fin helps killer whales maintain body temperature.