Premigratory Hyperphagia in Birds

Abstract

The unusual lipid metabolism of migratory birds is of interest in connection with human problems of obesity for two reasons : (1) lipogenesis and lipolysis are extremely rapid in some species and (2) temporary obesity can be readily induced experimentally by photoperiod manipulation. Wild birds appear to exhibit three patterns of migratory obesity: (1) short range migrants which attain moderate obesity but begin migration before peak deposition; (2) short range migrants which begin migration after peak deposition; (3) and long range migrants which become extremely obese (50 per cent of wet weight, 75 per cent or total dry weight or 300 per cent of non-fat dry weight of body composed of fats) just prior to long flights (such as over the Gulf of Mexico). Energy for the long flights is derived entirely from lipids. Experimental work so far has largely concerned short range migrants in which moderate hyperphagia and lipid deposition can be induced by direct stimulation of long photoperiods. New data obtained from birds killed during migration at television towers indicate that experimental work with long range species will prove instructive. A working but unproved hypothesis is that migratory obesity involves a temporary simultaneous alteration of both nervous pathways (i.e., hyperphagic-hypothalamic obesity) and metabolic pathways (i.e., metabolic type of obesity).