Weight Changes and the Mode of Depot Fat Accumulation in Migratory Short Tailed Shearwaters

Abstract

The time course of fat deposition in short-tailed shearwater breeding adults, immatures and chicks was determined by monitoring weight changes at the breeding site, and the relative importance of de novo fatty acid synthesis and direct incorporation of fatty acids from the diet was assessed by assaying enzymes associated with hepatic lipogenesis. Extensive fat deposition occurred only in the chicks during development, and all age classes deserted the breeding colony with relatively small reserves of depot fat. The absence of major changes in activities of hepatic lipogenic enzymes in the period between first land- fall in September and breeding site desertion indicates that fat deposition in all age classes occurs mainly through direct incorporation of fatty acids from the diet. Ecological and energetic implications of these findings are discussed.