|Erect-crested penguin breeding behaviour
In September 1998 Dr Lloyd Davis, Martin Renner and I travelled by yacht to the remote Antipodes Islands to study the erect crested penguin. We spent two months on the island, during which time we observed the penguins courtship, egg-laying and incubation in an effort to understand the odd breeding behaviour of crested penguins.
All crested penguins employ some form of brood reduction: two eggs are laid, but only one chick is usually fledged. This strategy is employed to varying degrees between the species, the Fiordland crested hatches both eggs, but one chick usually dies before fledging. A near neighbour to Fiordland, the Snares crested, hatches two chicks, but one dies within a few days of hatching. The erect-crested penguin carries this strategy to extremes - it lays two eggs, but only hatches one. Because it is the second or "B" egg that is usually hatched and raised to fledging, crested penguins put more resources into it. Again, this is carried to its extreme in the erect-crested, with the "B" egg being 40% larger than the "A" egg.
Our aim was to try and understand the reasons behind this brood reduction behaviour. Laying two eggs, but raising one may be looked on as a form of insurance but, if you only ever raise one chick, why bother to put energy into a redundant egg? Futhermore, it was thought that the first egg was deliberately ejected from the nest and we wanted to see if this was in fact the case.
We selected a group of around 160 pairs of ECPs that were nesting on a rock platform, below a rock pinnacle that provided us with a good seat and observation post. We then proceeded to band all the birds, measure their feet and bills (for sexing) and paint a large number on their backs for easy identification. Once banding was complete we started our behavioural observations. We observed the birds for 12 hours each day, splitting it up into 3-hour long shifts. Within the 3 hours, we tried to determine if which pairs had any egg, how many and who was incubating. We also recorded any mating for sexing and paternity reasons. Scans were also done of a sub-group of about 20 pairs every 15 minutes and their behaviour noted - sitting still, lying still, incubating, preening, fighting etc. We kept this up until after all the "B" eggs were laid and the males started to go to sea to feed after their 45 days ashore. We also made modifications to some nests in an effort to see if poor nest construction was a factor in egg loss.
What did we learn?
Our observations showed that ECP behaviour has some oddities and is, on the whole, rather violent. Fights for nest sites left some birds covered in mud and blood and the losers looking rather dejected. Despite the violence, birds were extremely faithful to their nest site and partner. It is now clear that the loss of the "A" egg is not deliberate, but a result of neglect and the mechanical dificulties of incubating one large and one small egg. We modified some nests to make it harder for the penguins to lose the "A" eggs, but they eventually rolled to the side and were ignored. It appears that the penguins are not hormonally prepared for the first egg and true incubation behaviour only occurs after the second egg is laid. The real reasons behind this method of brood reduction are still unknown. We hope to look at the breeding behaviour of other crested penguins in an effort to resolve this puzzle.
Story in Natural History Magazine by Lloyd Davis on the trip here >>>
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