Body Mass and Lipid Content at Nest-Leaving of European Starlings in New Zealand

Abstract

We investigated the relationship between body mass (i.e., wet mass) at nest-leaving and lipid content in 372 European Starling Sturnus vulgaris chicks in New Zealand to test the hypothesis that heavier chicks have greater lipid stores than lighter chicks, thereby enhancing their chances of surviving stressful periods after leaving the nest. Mass at nest-leaving ranged from 63 to 92 g. Total lipid content varied from 1.8 to 10.2 g, and increased as chick body mass increased up to 80 g, after which it leveled off. The lipid index (g lipid/g lean dry mass) varied from 0.106 to 0.470. The daily energy expenditures of fledglings of different masses were calculated to estimate the maximum number of hours that they could be sustained by their lipid stores after leaving the nest. Although the estimated fasting capability of the lightest chicks is only seven hours, most chicks (92%) had similar capacities of 15 to 20 h. This similarity in estimated fasting capability of most chicks is inconsistent with the hypothesis and may result from a compromise between the risks associated with carrying large lipid stores and the likelihood of encountering poor feeding conditions shortly after leaving the nest.