Keeping Cool
Measurement of giraffe body temperature has shown that it is ~38.5oC but it can vary by ~5oC over the course of a day. Body heat is derived from fermentation of browse, other metabolic processes and radiant heat. Heat loss mechanisms partly depend on body surface area. Despite their unusual shape the body surface area of giraffes is similar to that in other equivalent body mass mammals: a shorter trunk is offset by a longer neck and legs. Heat loss by radiation is constant, by conduction rare and minimal. Their long, slender legs and neck are an advantage for convective and evaporative heat loss from the skin: heat transfer is inversely proportional to the square root of diameter. Evaporation from the respiratory system occurs through the nasal mucosa, the surface area of which in giraffes is large. Cooling of the nasal mucosa and blood follows and cool blood drains in to the jugular vein and contributes to whole body cooling and cooling of the blood supplying the brain by heat exchange in the carotid rete. Similar heat exchange may occur across the surface of the ossicones. Behavior changes when ambient temperature exceeds skin temperature. Giraffes re-orientate their bodies to minimize radiant heat gain and seek shade. A unique arrangement of blood vessels supplying blood to skin patches allows patches to act as thermal windows through which heat can be lost an arrangement enhanced by evaporation: sweat gland density in the skin of patches is greater than it is elsewhere.