Mystery Surrounding Penguin Egg Rejection Finally Explained

Featured in Ripley’s Believe It or Not!

One of the most enigmatic birds on the planet is the erect-crested penguin. Native to New Zealand, this highly isolated species hasn’t been well studied over the years, which means many mysteries still surround them.

At the top of the list is what they do with the first set of eggs laid during mating season — instead of carefully incubating them, the penguins discard them, demonstrating a level of disinterest toward potential offspring rarely seen in the animal kingdom.

Until recently, scientists felt confounded by this behavior. After all, egg laying requires lots of energy. And energy isn’t something animals like to waste, especially when survival is on the line. Nevertheless, the penguins keep ditching eggs, and now scientists have an explanation for this behavior. Here’s what researchers have learned about these fascinating and remote birds.

The Forgotten Penguins

Studying erect-crested penguins is far from an easy task, thanks to geography. The birds inhabit New Zealand’s Antipodes and Bounty Islands, little more than rocky outcroppings located along the southeastern coast of the South Pacific Ocean.

But a group of scientists from the University of Otago in New Zealand has spent an impressive 250 hours observing these so-called “forgotten penguins,” a research effort first spearheaded in 1998. Their observations over the decades have led to some surprising and fascinating discoveries, especially regarding reproductive habits.

First Chicks Need Not Apply

According to Lloyd Davis, the lead author of the scientists’ most recent study, erect-crested penguins treat the first egg they lay as disposable. In nearly half of all cases, mother penguins make no effort to build a nest or incubate them. And 90 percent of these mothers lay their first eggs atop an uneven rock platform, more or less guaranteeing they’ll roll away.

So, what’s wrong with the erect-crested penguins’ first eggs? For starters, they’re significantly smaller than the birds’ second round of eggs. This bucks a common trend found in avifauna. As Davis explains, “In most birds, the clutch [of eggs] gets smaller as they’re laid, but in this case, the second egg is on average 85 percent larger than the first one.” The penguins’ weirdness doesn’t end there.

The difference in sizes of eggs within a clutch of erect-crested penguins, with the first-laid egg being far smaller than the second-laid egg. Credit: Lloyd Davis Photography (www.lloyddavis.com), CC-BY 4.0.

Docile Males During Mating Season

Throughout the animal kingdom, the advent of mating season ushers in aggressive and competitive behavior among males. From head-butting rams to fighting lions, displays of strength and dominance are considered normal. The same goes for countless bird species… except for erect-crested penguins.

As Davis explains, “Normally, you would expect the males to have higher testosterone levels at the start of the breeding period, while the females’ levels would be lower, but we found something different.” As it turns out, the female penguins had more testosterone in their systems than their male counterparts, especially during the egg-laying period.

Scientists believe this might be why male erect-crested penguins buck the aggressive trend at mating season, acting downright docile around their lady friends and one another. Of course, this is just the tip of the iceberg when it comes to unanswered questions related to these unique birds. Davis means it when he declares, “They’re an enigma.”

By Engrid Barnett, contributor for Ripleys.com

Source: Mystery Surrounding Penguin Egg Rejection Finally Explained