THE ENERGETICS OF MIGRATION AND REPRODUCTION OF DUSKY CANADA GEESE

We analyzed the carcass composition of 160 adult female Dusky Canada Geese (Branta canadensis occidentalis) collected in Oregon and Alaska from 1977 to 1979, to determine energy use patterns from premigration to hatch. We tested the predictions that geese would accumulate energy reserves during migration, experience a gradual loss during prelaying and a severe loss during laying and incubation, Energy requirements met from food were estimated by comparing changes in endogenous reserves to estimated daily energy requirements. Body mass, and water, lipid and protein components varied by stage of reproduction (P = 0.0001), and protein also varied by year (P = 0.0001). The brief migration period was costly, with a 52% decline in lipids, indicating that strategies to meet these energy demands are pivotal and will influence subsequent energy dynamics of reproduction. Geese maintained or increased lipid and protein reserves during the prelaying period, gradually lost reserves during laying and experienced considerable declines during incubation. Use of food for energy and nutrient requirements was important at all stages, accounting for 24% during incubation, the smallest but perhaps most critical contribution, to 100% during prelaying, of estimate daily energy requirements. The contribution of exogenous (food), versus endogenous sources, to energy and nutrient requirements of northern nesting geese is proving to be much more important than previously thought.