S25.Summary: Physiological approaches to ecological questions about water and energy in birds

Energy or water availability frequently impose constraints on birds due to the relatively large amounts required compared to what is immediately available from the environment, or because of limitations on the physiological processing capacities of the birds. Thus, adjustment of behaviour may become an important factor in maximising the efficiency of utilisation of critical resources and extending endurance limits. Further, the acquisition of water and regulation of its balance in the body may be closely linked to energy acquisition and use, through preformed water in food or metabolic water production.

Historically, the success of this research program stems from a solid foundation of empirical studies in comparative physiology. These studies permitted inter- and intra-specific comparisons of physiological performance, particularly in extreme environments, but allowed limited ecological conclusions to be drawn. While it is now recognised that the effects of phylogeny must be considered in interpretation, the approach remains useful in identifying general patterns and specific adaptive solutions to particular environmental conditions.

More recent research combined laboratory and field physiological measurements, microclimate data and biophysical models, to draw broader, more ecologically relevant conclusions about the species' fundamental niche. The description of new physiological capacities has frequently followed new technological developments particularly in electronics and analytic techniques. This has frequently allowed measurement or monitoring of physiological function of birds under conditions where it was previously impossible. Further progress in the discipline has been by way of measuring physiological performance in manipulative field experiments. Such studies permit more extensive inferences to be made, directed towards solving problems based in contemporary ecological theory. They also permit the integration of concepts in physiology and evolutionary ecology using optimality theory to make predictions about which physiological strategies should be favoured in particular ecological circumstances.

The five papers in this symposium illustrate this broad-spectrum of approaches used in addressing questions in this field of avian physiological ecology. Centred on one of the major tenets of modern ecology, these studies are ultimately directed toward understanding how physiological constraints limit the abundance and distribution of birds.