Breeding
Crested penguins breed on subantarctic islands in the southern reaches of the world's oceans; the greatest diversity occurring around New Zealand and surrounding islands. Their breeding displays and behaviours are generally more complex than other penguin species. Both male and female parents take shifts incubating eggs and young.
Crested penguins lay two eggs but almost always raise only one young successfully. All species exhibit the odd phenomenon of egg-size dimorphism in breeding; the first egg (or A-egg) laid is substantially smaller than the second egg (B-egg). This is most extreme in the Macaroni Penguin, where the first egg averages only 60% the size of the second. The reason for this is a mystery, although several theories have been proposed, remains unknown. British ornithologist David Lack theorized the genus was evolving toward the laying of a one-egg clutch. Experiments with egg substitution have shown that A-eggs can produce viable chicks which were only 7% lighter at time of fledging.
Recently, brooding Royal and Erect-crested Penguins have been reported to tip the smaller eggs out as the second is laid.
Read more about this topic: Crested Penguin
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