The breeding biology of Eudyptes penguins with particular reference to egg-size dimorphism

Williams, Anthony John

The breeding biology of Eudyptes penguins with particular reference to egg-size dimorphism

Doctoral Thesis

1980

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

The breeding biology of Macaroni Penguins Eudyptes chrysolophus and of Rockhopper Penguins E. chrysocome was studied at Marion Island (46°54'8, 37°45'E) in the austral summers of 1974-75 and 1976-77. The clutch comprises two eggs, the first-laid (A-) egg being markedly smaller than the second-laid (B-) egg. Components of B-eggs are heavier than the same components of A-eggs. Incubation begins after the B-egg is laid. Incubation of B-eggs lasts 34 and 36 days in Rockhopper and Macaroni Penguins respectively. Parents treat the larger egg preferentially. In Macaroni Penguins, less than 1% of all A-eggs hatch and 54% of all A-eggs are lost before the B-egg in the same clutch is laid. In Rockhopper Penguins, both eggs are retained until one hatches at 30% of all nests, but both eggs hatch at only 12% of all nests. The B-egg hatches before the A-egg. Hatchling weight and the growth of chicks for the first 35 days after hatching are correlated with egg weight. B-egg chicks grow significantly faster than A-egg chicks and are heavier within 24 h of "fledging". Chicks of both species are fed at intervals of 36-92 hours and receive about 30 meals during the 70-day chick-rearing period. Except in exceptional circumstances, Macaroni Penguins rear no A-egg chicks. When two Rockhopper Penguin chicks hatch from dimorphic eggs, one dies of starvation within 12 days but in experiments chicks hatched from two eggs of similar size co-existed for up to 57 days. Chicks are raised successfully from 3% of all A-eggs laid by Rockhopper Penguins, and from 34% and 43% of all B-eggs laid by Rockhopper and Macaroni Penguins respectively. Only one chick can be reared from each clutch. Egg-size dimorphism predetermines the offspring most likely to survive. Eudyptes penguins may forage 100 km from the colony when feeding chicks. However, the ancestral Eudyptes was probably an inshore-feeder laying two eggs of similar size and capable of raising two chicks. Egg-size dimorphism has probably developed through major enlargement of the B-egg, and possibly arose in the course of the transition from inshore to offshore foraging.

Keywords

Zoology

Reference:

Collections

PhD / Doctoral

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