Breeding and moulting fasts in macaroni penguins: Do birds exhaust their fat reserves?

1. Plasma concentrations of urea, uric acid and total lipid were compared in pre- and late-fast breeding and moulting macaroni penguins (Eudyptes chrysolophus) to test the hypothesis that birds exhaust their lipid reserves and initiate marked protein utilisation towards the end of natural fasts. 2. Male and female macaroni penguins fasted for a minimum of 29–32 days and 20 days during the breeding and moult fasts, and the difference in body weight over the sample period (reflecting body weight loss) was 31–34% and 41–47%, respectively. 3. There was no significant increase in plasma urea or uric acid at the end of either fast, nor any decrease in plasma lipid concentrations compared to pre-fast birds. 4. These results suggest that macaroni penguins continue to rely mainly on lipid reserves during the later stages of natural fasts. This is consistent with post-fast body composition data for other small penguin species.

Details