Gessaman, J.A. & Piersma, T. 1999. Nutrient store dynamics and functional ecology of intra-individual compositional changes. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 1. Johannesburg: BirdLife South Africa.

One of the greatest hindrances to studies of avian ecological energetics is the lack of an accurate non-destructive or non-invasive technique for determining whole body fat and protein storage. Fat, which has an energy content of about 2.5 times that of protein or carbohydrate per unit dry mass and about 8 times per unit wet mass, is the main energy store in birds. However, the important role of protein as a source of nutrition and energy has become clearer in recent years. Although measurement of daily energy expenditure (DEE) typically has errors of plus or minus 8 percent, non-lethal measurements of fat or protein storage often have a larger percent error. A 10% error in fat storage is equivalent to 1 to 2 times the DEE of birds with 5 percent body fat that weigh from 100 to 1000 g, and it represents larger multiples of DEE for larger and fatter birds, e.g. the error is about 12 times DEE for a 1 000 g bird with 25% body fat. Will this kind of error allow you to measure anticipated changes in the body fat of your study species with the accuracy needed to test your hypotheses or to clearly discriminate significant changes in body fat associated with seasonal events or life cycle stages of individual birds? This symposium will delineate the accuracy of lethal and nonlethal methods of measuring fat and protein and will explore questions in avian ecology that are being addressed with the current technology.