Seasonal changes in body mass, body composition and food requirements in wild migratory birds.

Abstract

Some species of small migrant songbirds and shorebirds undergo seasonal changes in body mass which are proportionately greater and more rapid than those known in any other adult vertebrates. Within a 2-3-week period before migration they may double in total body mass, but after 2-3 d of flight return to starting mass (Davidson & Evans, 1988; Alerstam & Lindstrom, 1990). These changes occur largely through the deposition and utilization of fat as fuel for sustained flight. However, it has been accepted for some time that many species of goose store not only fat but also protein before spring migration (McLandress & Raveling, 1981). Although earlier studies of most migratory songbirds suggested that fat was the only component that varied (e.g. Connell etul. 1960; Odum et al. 1964), more recent information shows that in several species lean mass also increases before migration (for summary, see Piersma, 1990). In the present paper we review information on seasonal changes in body mass and body composition of migrating birds and how they are brought about in terms of nutrient supplies; and we discuss what sets the limits to these changes and how body mass may be regulated both proximately and ultimately.