ABSTRACT
Most animals simply assume the temperature of their immediate external environment, but birds and mammals regulate their body temperature and maintain it at a relatively constant level which is different to that of their immediate external environment. Essentially, birds and mammals are endotherms and all other animals are ectotherms. The thermoregulatory problems facing terrestrial ectotherms are rather different from those of aquatic ectotherms. The most important way in which terrestrial ectotherms obtain heat is by the absorption of solar radiation. On the basis of ‘selective’ lesioning experiments, it has been proposed that the different regions of the hypothalamus perform different thermoregulatory functions. It is inevitable that animals will interact with their immediate thermal environment – there will be some heat exchange between the two. There are four possible ways by which animals can exchange heat with the environment: conduction, convection, radiation and evaporation.
