These Penguins Mysteriously Abandon Their First Egg. We Finally Know Why

The least studied penguins lay two eggs and abandon the first one.

The first egg laid by erect-crested penguins is usually rolled away. Sometimes, the female will abandon their first born in order to push it out of the house.

Only the researchers who first conducted the fieldwork on the penguin's remote, uninhabited islands think they understand what's going on.

Subantarctic penguins, whose numbers have declined sharply in the last 50 years, are forced into infanticide because they can't find the same amount of krill and squid as their ancestors, according to a reanalysis of old data.

The penguins lay smaller eggs than the mothers choose to keep. The researchers behind the new study think the earlier egg is smaller because it is formed while the birds are still in New Zealand. Five days after the first, the second one is laid.

The egg size difference is uncommon for most birds. It's the first egg that tends to be larger if females produce more than one.

The data on the erect-crested penguins is decades old, but they are overlooked because of their remote habitats.

It's not helped by the fact that little is known about the birds. The 1998 study is still the most detailed one available, according to the researchers.

Understanding how these birds breed is important to their survival. The penguins may be suffering from an evolutionary hangover that no longer works in the modern world and are trying to adapt.

The features of 'egg B' give it an advantage over the earlier laid 'egg A'. These penguins prefer to put the larger one at the back of the brood patch when they are ready to lay their eggs.

Egg B's size indicates to the mother that the chick may provide it with more sustenance, which could help it survive.

Most of the A-eggs were lost before or on the day that egg B was laid. Within a week, the rest were gone.

Eggs were laid directly on the ground more than 90 percent of the time.

The researchers decided to experiment with penguins in a different colony.

The team placed a ring of stones around 14 'nests' to stop the A-eggs from rolling away.

The A-eggs in the manipulated nest did not survive anymore. All of the eggs were lost.

More than half of the A-eggs were broken when the human-made ring of stones was present. In the untouched group, the eggs were rolled away, while others went missing, most likely from the slope of the island where the colony was breeding.

Many of the birds didn't even bother to put an egg in it.

The authors conclude that low levels of reproductive readiness amongst erect-crested penguins arriving at the colony points to low levels of copulation.

The findings are not in line with two of the main hypotheses on the penguin's behavior.

The idea that A-eggs are lost to fighting during the courting period is not true based on behavior and hormones.

The first-laid eggs act as insurance against the loss of larger second-borns, according to the other hypothesis.

Researchers argue that this is not likely. Natural selection could reduce the clutch size if food became harder to find. The birds wouldn't lay another egg.

The second egg seems to be favored by selection.

The best way for crested penguins to reduce investment in the first egg is to have another egg.

The largest egg-size dimorphism of all penguins is found in erect-crested penguins.

The researchers say that the penguin should be so little known that it's a contradiction.

It's a pity.

There was a study published.