Erect-crested penguins always reject their first egg and lay another

A little-known species of penguin only has the resources to raise one offspring, but an evolutionary quirk means they focus their investment on the second egg

By Alice Klein

Erect-crested penguins

Lloyd Davis/University of Otago

Members of a little-known species of penguin always reject the first egg they lay, possibly because they only have enough food to rear one chick and their second egg has a survival edge.

The erect-crested penguin (Eudyptes sclateri), which is named for the upright yellow feathers on its head, is the least-studied penguin in the world because it lives on two island groups between New Zealand and Antarctica that are “about as far from civilisation as you can get”, says Lloyd Davis at the University of Otago in New Zealand.

In 1998, Davis and two of his colleagues spent six weeks studying the penguins on Antipodes Island, a rugged windswept island located 860 kilometres south-east of New Zealand.

“It has massive cliffs around it and no real landing spot for a boat, so we jumped into the surf with all our gear and dragged it up the 200-foot-high cliffs,” says Davis.

The team found that female erect-crested penguins lay two very different-sized eggs about five days apart – the second 85 per cent heavier than the first. The first egg never hatches because it is ignored or actively pushed away. The second, however, is carefully incubated by the female and usually results in a chick.

“It’s really bizarre behaviour – it’s like they don’t care about the first egg at all,” says Davis.

The penguins’ first and second eggs

Lloyd Davis/University of Otago

He presented the results at several conferences but didn’t formally publish them, instead moving into filmmaking and science communication. Recently, he and his colleagues decided to reanalyse their data to try to understand the mysterious behaviour of the penguins, which have never been studied in detail again.

Other biologists have speculated that the penguins lay two eggs as an insurance policy in case one gets broken, perhaps by fighting males.

However, the team found that fighting was uncommon. What’s more, 80 per cent of first eggs were lost before or just after the second one was laid, because they had rolled away or been deliberately pecked at or broken. This suggested that the two eggs didn’t provide an insurance function.

Instead, the researchers believe that erect-crested penguins inherited a two-egg reproductive strategy from their ancestors but no longer have the resources to invest in both eggs, since their remoteness means they have to swim long distances to find food.

The obvious solution would be to just lay one egg, but the penguins seem to be hard-wired to favour the second egg, says Davis, perhaps for reasons lost in their evolutionary past.

“If there’s something that causes you to favour the second egg then you’re stumped, because you can’t have a second egg without having a first – all you can do is reduce investment in the first egg,” he says.

This may be why the first egg is far smaller than the second –  there’s no point investing much energy in an egg that has to be discarded anyway, he says.

Erect-crested penguins are also unusual because their copulation rate is one-tenth that of other penguins – “they just sort of stand around looking disinterested,” says Davis – and they tend to lay their eggs straight onto bare rock instead of creating nests out of grass or twigs.

In 2014, another research group counted the penguins’ nests on Antipodes Island and found that their population size had declined by about one-third since Davis and his colleagues visited in 1998.

This may be due to climate change affecting food availability. “We know that comparable species go a long way to forage at fronts between different water systems that create upwellings containing a lot of food, and changing temperatures can affect where these fronts are found,” says Davis.

The finding that erect-crested penguins could be in trouble should be a wake-up call to fund more research to better understand them, he says. “I think it’s appalling that our study from nearly a quarter of a century ago is still the most detailed by far,” he says. “These are stunning birds and they have this bizarre behaviour, but we know almost nothing about them.”

Journal reference: PLOS ONE, DOI: 10.1371/journal.pone.0275106

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