Methods of studying the functional ecology of protein and organ dynamics in birds

Birds are capable of adaptive responses to ecological challenges involving changes in body composition, including both body stores and functional tissues. These physiological adjustments may affect aspects of the birds’ ecology, such as choice of diet and microhabitat or susceptibility to aerial predators. Carcass analysis provides accurate data on body composition; however, ethical considerations apart, this method neither enables studies of temporal changes within individuals nor allows compositional analyses to be followed up by studies on the birds’ life history. Various non-terminal methods are available to quantify gross body composition in terms of fat, protein, and water. In addition, energy and mass (nitrogen) balance measurements in caged song birds and shorebirds provide sensitive and robust methods to estimate protein and fat contents of anabolised and catabolised body stores, albeit under laboratory conditions rather than in the field. The potential of new non-terminal methods (i.e. ultrasound, nuclear magnetic resonance imaging and computer tomography), which allow repeated size estimation of various organs, was evaluated in recent studies on shorebirds and swans. These methods probably have the greatest potential in break-through studies in the field of ecophysiological adaptation, because they allow non-invasive, repeated quantification of the size of different organs in individual birds.