Fat Storage and Fat Metabolism in Relation to Migration

Abstract

The pivotal role played by fat in suppyling energy for migration in birds has been appreciated for nearly 4 decades and reviewed extensively (Odum and Perkinson 1951; King and Farner 1956; Berthold 1976; Blem 1976, 1980; Dawson et al. 1983). The basic biochemistry, physiology, and bioenergetics of migratory fattening have been identified; yet, the regulatory mechanisms involved remain obscure. On the one hand, the behavioral and physiological functions associated with migration are thought by some to be an expression of an endogenous (genetic) program that relies little upon cues from the environment (Berthold 1985). Conversely, environmental information is regarded by others as playing an instrumental role in the regulation of such migratory functions as hyperphagia, fattening, and Zugunruhe (nocturnal restlessness) (Stetson and Erickson 1972; Schwabl and Farner 1989a,b; Wingfield, this Vol.). Recently, Wingfield et al. (this Vol.) proposed a scheme for classifying environmental and endogenous factors that regulate migratory phenomenon. Specifically, vernal (spring) fattening is triggered by initial predictive factors that include an increase in photoperiod and endogenous programs (Wingfield et al., this Vol.). However, the supplementary factors that guide the progression and termination of both vernal and autumnal fattening are not well understood.