Giraffe Thermoregulation: a review

Abstract

The ability to maintain a relatively constant body temperature is central to the survival of mammals. Giraffes are found in relatively hot rather than cold environments, have a body temperature of 38.5 ± 0.5°C, and must have evolved appropriate thermoregulatory mechanisms to maintain this temperature and to survive in their chosen habitats. Their thermoregulation depends on anatomical features and behavioural and physiological mechanisms. To minimize physiological thermoregulation giraffes orientate their bodies to optimize radiant heat gain and to maximize convective heat loss, and seek shade. Their long and slender, “dolicomorphic” shape by increasing body surface area without proportionally increasing their metabolic mass enhances heat loss mechanisms. Their ossicones are well vascularized and may also function as a thermoregulatory organ. The main physiological mechanism for achieving heat loss is evaporation. Giraffe nasal anatomy and their unique respiratory system can combine to cause high respiratory evaporative heat loss and, theoretically, cooling of jugular venous blood. Evaporation of sweat is another heat loss mechanism but has not before been reported to occur in giraffes. We have analysed the anatomy of giraffe skin and show that it contains many active sweat glands, and that the size of these glands is significantly greater under patches than it is elsewhere. Giraffes therefore can and in some circumstances will sweat. When combined with the anatomy of the blood vessels supplying patches these data further support the idea that patches are thermal windows. We conclude that giraffe have evolved an array of thermoregulatory mechanisms, mostly to achieve heat loss, which make them well adapted to hot and arid environments.