Mechanisms of brood reduction in Fiordland crested penguins (Eudyptes pachyrhynchus)

Abstract

Mechanisms of brood reduction were studied in Fiordland crested penguins (Eudyptes pachyrhynchus) on Open Bay Islands from July through October 1989. I quantified behavioural and environmental causes of egg and chick loss at the time of laying, during incubation, and after hatching to evaluate hypotheses advanced to explain the unique patterns of hatching asynchrony and egg dimorphism in eudyptid penguins. Although first eggs experienced lower survival than second eggs and most losses occurred during the laying interval, aggression between adult penguins did not appear to contribute to egg loss at any time. Similarly, egg mortality was not influenced by the effects of nest crowding or cover, or by the degree of intraclutch egg dimorphism. Egg temperatures were measured throughout the incubation period with thermocouples implanted in preserved eggs. Recorded temperatures increased markedly after the laying of the second natural egg, but did not differ between eggs of different sizes within a nest. First eggs were not consistently incubated in the anterior nest position and that position did not confer a thermal disadvantage. However, first eggs hatched later than second eggs. Retarded brood patch development may contribute to lower egg temperatures during the laying interval. Chicks from larger, second-laid eggs were larger at hatching, and grew more rapidly than their siblings. Overt aggression between feeding chicks was not observed and begging and feeding rates appeared to be similar. Nonetheless, large chicks experienced higher survival to the creche stage. Intra-clutch egg dimorphism was negatively correlated with the number of days two chicks survived in the same nest, but there was no relationship between survival and hatching asynchrony.