As global temperatures rise, the lives of countless plants and animals are changing in response. That includes king penguins, which a new study predicts will see profound, climate-driven changes in their numbers and the location of their breeding grounds over the next century.
King penguins (Aptenodytes patagonicus) live and breed on a collection of small, rocky islands that ring Antarctica, in a swath of frigid maritime territory known as the “subantarctic.” The birds feast on small fish and squid in nearby waters, which exist in rich quantities because of the Antarctic Polar Front (APF), a convergence of warmer water from the subantarctic meeting the colder waters surrounding Antarctica. This zone experiences nutrient-heavy upwelling, supporting great swarms of plankton and krill, which drive the subantarctic food web.
As the world gets warmer, the APF is expected to drift further and further south. But king penguins can’t just gradually follow the poleward migration of their hunting grounds, because their breeding grounds are static, on ice-free parts of islands. They have to use other islands as stepping stones. Research published today in the journal Nature Climate Change makes predictions about how this challenge will unfold over the 21st century, suggesting that most of the species will be stuck between a rock island and a hard place: either they abruptly move to other islands, or die out.
The researchers used information about king penguin ecology and historical population trends, as well as climatic forecasts, to model where king penguins could be expected to persist by the year 2100. Then, they used DNA to reconstruct the prehistorical population trends of the species. When they compared the thousands of years of population shrinkage, rebounding, and migration with their model, the researchers determined that king penguins suffered extreme consequences from past climate change acting on the extent of sea ice, and the location of the APF.
Their predictions are startling. Under warming produced by “business-as-usual” greenhouse gas emission levels, many northern islands may be totally abandoned due to the waning foraging grounds. Since king penguins take a long time to reproduce, and their current genetic diversity is very low, they aren’t expected to adapt fast enough to deal with the shifting food source. This means that about 70 percent of the species’ 1.6 million breeding pairs would be threatened with survival by 2100.
Forty nine percent of all penguins would outright lose their habitats. Another 21 percent, mostly breeding on islands off of the tip of South America, would experience dramatic alterations in their habitat quality as foraging grounds become nearly too far away to access.
While this is a grim vision of the future, it’s not known how much of this loss could be recouped by penguin resettlement and population regrowth. Today, Bouvet Island in the South Atlantic is too ice-bound to support a king penguin colony, but with elevated temperatures, it could become ripe for colonization. Other places like South Georgia could see swelling populations as foraging conditions improve there.
It’s also possible that the model is too conservative, because it can’t take into account every potential repercussion of climate change. For example, ocean acidification, or changes in global ocean circulation processes, could mess with plankton numbers, throwing feeding grounds into chaos. Also, even if the penguins successfully colonize other islands, we don’t know how new competition with other native penguins would influence the long-term survival of those birds.
Either way, this approach to understanding how cold-adapted species in fragmented habitats cope with climate change may be useful for predicting responses in other species with disjointed distributions. It certainly reminds us that the impacts of climate change will ripple far beyond humans.