Emperor penguins are experiencing reproductive failure en masse because the sea ice crumbles under their feet before their young have waterproof plumage

In as many as a fifth of all colonies in Antarctica, emperor penguins saw many of their young die this year. And some of those colonies don’t even seem to have successfully raised a single young this year.

This is what researchers say in the magazine AntarcticScience. They rely on satellite images.

Satellite images
The penguins themselves cannot be seen in those images. But their presence can be deduced from brown spots on the ice: excrement that the penguins leave behind. Based on these brown spots, researchers can determine where the penguins hang out and on which areas of sea ice, for example, they hatch their eggs and raise their young (see box).

Emperor penguins depend on sea ice that is firmly attached to land for reproduction. They colonize the sea ice around the end of March and the beginning of April and lay their eggs there in May or June. Those eggs hatch after about 65 days. In the subsequent period, the penguins are highly dependent on their parents, including for food; Because they do not have waterproof plumage, they cannot leave the sea ice. Only in December or January are the young penguins able to enter the water, leave the breeding ground and in fact ‘fly out’. For successful reproduction, it is therefore important that the sea ice remains stable between April and January.

From the satellite images, the researchers could not only see where the penguins hung out during the breeding season, but also how the sea ice behaved in those places during the breeding season. And in some places they saw the sea ice where the penguins had nested disappear (almost) completely before the end of the breeding season. And that is a strong indication that some or even all of the young from such a colony should be considered lost, the researchers write. “We assume that if sea ice breaks up before the young fledge and the sea surface is clearly visible, without the presence of large, stable ice floes or substantial pack ice, this will result in a total or near-total failure of reproduction. It is often the case that if large ice floes remain, young can survive. Although it has also been suggested that such pieces of ice become too mobile and move so far from the colony that parents are no longer able to find their young.”

Twenty percent
It is quite a tragic story, which – as the research shows – unfolded last year in various colonies of emperor penguins. In total, the researchers looked at 66 colonies off the coast of Antarctica. And 14 of them turned out to be related to the premature breakup of sea ice. It means that about 20 percent of colonies lost young. And 6 of them even seem to have lost all their young.

Earlier years
And that tragic story is not an isolated one. Because for six years in a row, researchers have been monitoring the reproductive success – or lack thereof – of emperor penguins. And they are starting to see a clear trend. Namely that more and more colonies are losing young, because the sea ice crumbles under their feet during the breeding season and the young are not yet ready to enter the water.

Smaller population threatens
It should be noted that 2023 was not the worst year ever for emperor penguin reproduction. That dubious honor is reserved for the year 2022, when almost 30 percent of colonies lost newborn chicks due to premature sea ice melting. However, that doesn’t detract from the larger trend the researchers see, which is that prematurely melting sea ice is a growing problem for emperor penguins. “As the continent continues to warm, we see the ice breaking up sooner, leading to increased chick mortality,” said researcher Peter Fretwell. “And if fewer chicks survive in many colonies, it seems likely that eventually some of the current breeding sites will no longer be usable and the overall population will shrink.” That is also a picture of the future that climate models have been sketching for some time. If we don’t limit our emissions, the population will be 99 percent smaller by the year 2100 and essentially doomed.

At the same time, it also means that this doomsday scenario is not a given; we can still change it by reducing our emissions. And perhaps the penguins themselves can also contribute by adapting somewhat to the changes in their habitat. There are tentative indications that the birds may be capable of this. For example, some colonies that produced little or no young last year appeared to have chosen a different place to hatch their eggs this year. “The fact that we are seeing these adaptations within the hardest-hit colonies gives us some hope that the birds can respond to their changing environment and move to find more stable ice,” Fretwell said.