Plasma metabolites in macaroni penguins (Eudyptes chrysolophus) arriving on land for breeding and moulting

1. Plasma metabolites and nutrients of macaroni penguins (Eudyptes chrysolophus) arriving on land in good condition, following intense feeding, for breeding and moulting were investigated. 2. The pre-breeding female birds had significantly higher concentrations of total lipid, iron, magnesium, calcium, inorganic phosphate and alkaline phosphatase, and lower concentrations of total cholesterol, all-trans retinol (vitamin A) than the pre-breeding males. 3. With the exception of iron, which was lower in the male, the various parameters measured in male and female pre-moult penguins did not differ. 4. Some of the plasma metabolite concentrations of the pre-moult birds differed substantially from those of their male and female pre-breeding counterparts. 5. The observed differences were thought to be the result of mobilization in response to physiological demands for egg formation and moulting. 6. However, it is possible that discrepancies were partly due to selective ingestion of nutrients in preparation for higher physiological demands