Ecophysiology attempts to clarify the role and importance of physiological processes, such as digestion and respiration, in the ecological relations of species in their natural habitats. The basic principles and methods that are central to any ecophysiological study are outlined and discussed, including animal capture, blood collection, and the measurement of plasma components and hormone levels. Attention is paid to animal welfare and ethical considerations, and the question of stress and how to identify its presence in animals in their natural environment is approached through a series of case studies. Examples are given from a wide range of vertebrates living in deserts, cold climates and oceans, and recent findings on the physiological adaptations of Antarctic birds and mammals are a highlight of the book. This textbook will provide an introduction to the study of ecophysiology for advanced undergraduates and postgraduate students, as well as researchers in ecology, biodiversity and conservation.