the then emerging field of avian energetics. The symposium featured papers by James R. King, William A. Calder III, Vance A. Tucker, and Robert E. Ricklefs and com­ mentaries by George A. Bartholomew, S. Charles Kendeigh, and Eugene P. Odum. The proceedings of the symposium, Avian Energetics (Paynter 1974), played a critical role in stimulating interest and research in the field of avian energetics. Some twenty-odd years later, we are making another attempt to summarize the information in the field of avian energetics. Some obvious differences exist be­ tween its predecessor and this volume. Numerous improvements in methodology, such as the use of doubly labeled water to estimate metabolism in free-living birds, now allow researchers to ask questions that could not be addressed previ­ ously. Second, consideration of nutrition is now inseparable from that of energet­ ics. This merger is necessary not only because food intake is the source of both en­ ergy and nutrients but also because one or more nutrients, rather than energy, can be limiting for a given species in a particular instance. Finally, the study of ener­ getics and nutritional ecology, particularly in birds and mammals, has grown so dramatically that a single volume can now only partially cover the range of possi­ ble topics and can catalogue only a sampling of all the studies on the subject.

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