King penguins back from the foraging trip. (T. Powolny)

Penguins are the cuddly faces of the Southern Hemisphere and among the most recognizable birds known to brave the chilly Southern Ocean. But like so many other charismatic favorites of the animal kingdom — especially those that inhabit the world’s coldest places — they’re starting to suffer the effects of climate change.

The king penguin, an iconic black, white and yellow bird second only in size to the emperor penguin, is among the latest species to feel the heat. King penguins raise their chicks on the sub-Antarctic islands north of Antarctica and dive for fish in the frigid waters at the northern reaches of the Southern Ocean. But their breeding and foraging behaviors may be at risk as ocean temperatures heat up in the Southern Hemisphere. New research shows that warm sea-surface temperature anomalies in the region can cause shifts in the marine environment where they feed, forcing the birds to travel farther and dive deeper for their food — and causing declines in their populations.

Variations in the climate of the southern Indian and Atlantic oceans depend on several important factors. These include the influences of El Niño and La Niña, which cause phases of warmer and cooler temperatures, as well as changes in atmospheric conditions in the Southern Hemisphere known as the Southern Annular Mode. These kinds of climatic variations can cause sea-surface temperatures to rise and fall from one year to the next. And these temperature changes can, in turn, change marine ecosystems by driving fish and other organisms into different regions. 

A study published Tuesday in the journal Nature Communications shows that these climatic changes — and their resulting effects on marine food webs — can have serious implications for king penguin populations. Looking at these natural oscillations can give scientists an idea of what to expect as temperature changes in the future become increasingly driven by climate change, which will shift climatic variations definitively toward a warming trend.

King penguins typically forage for food in an area of the Southern Ocean known as the Antarctic polar front, a region where the colder water in the south meets the warmer water to the north and draws an abundance of plankton, krill and fish. In some years, though, if sea-surface temperatures in the northern part of the Southern Ocean get too warm, the polar front can be pushed southward. This means king penguins have to travel farther from their island homes to get to the best feeding areas.

The study’s authors, led by Charles Bost of the Chize Centre for Biological Studies at the French National Centre for Scientific Research, tracked the foraging patterns of king penguins living on the Crozet archipelago in the southern Indian Ocean between 1992 and 2010. They wanted to find out how sea-surface temperature changes might affect the birds’ foraging behavior, and whether changes in their behavior could also affect their population sizes and reproductive success. The study may be among the first to provide “information at the same time on the at-sea movements, diving, breeding success and long-term population dynamics” of king penguins in response to climatic changes, lead author Bost told The Washington Post.

The researchers found that in warm years, the Antarctic polar front shifted south — in fact, a 1-degree Celsius increase in sea-surface temperature caused the front to move south by 130 kilometers (or about 80 miles) — forcing the penguins to travel significantly farther to get to their prime feeding grounds. This is especially problematic for the birds during breeding season, when penguin parents take turns incubating eggs and raising chicks and must travel back and forth between the islands and the polar front much more often to relieve their partners of parenting duties, a time-consuming and exhausting endeavor.

The research suggests that having to travel so much farther on these foraging trips could have damaging effects on the king penguin population. In 1997, the southern Indian Ocean experienced a particularly unusual El Niño-driven warming event, which drove the polar front south and forced king penguins to travel twice their normal distance during foraging trips. The researchers observed that they also dove about 30 meters deeper for their food in this year compared with other years.

Many penguins did not survive these extreme conditions. In the same year, the researchers observed a 34 percent decline in the adult king penguin population — a loss so severe that it took the population five years to work its way back up to pre-1997 numbers. The penguins’ breeding success was also lower that year than at any other time throughout the study period.

The study didn’t include observations of fish or other prey, but the researchers note that the changes in penguin foraging behavior — and the subsequent effects on the penguin population, itself — were probably driven by changes in prey availability, as fish in the region almost certainly migrated to follow the shifting polar front. This behavior would be consistent with many previous studies, which have shown that changing ocean temperatures are capable of driving marine animals outside their typical ranges in search of more suitable conditions.

This is worrying news, because global climate change is only expected to continue driving ocean temperatures up, particular in the Earth’s polar regions. If prey species continue to migrate in response to the shifting climate, then king penguins won’t be the only species affected; additional predators, such as other seabirds or seals, will likely also be affected.

The authors wrote: “Future climatic scenarios indicate a warming of the surface waters that should lead to a progressive southward shift of the [polar front]…and potentially representing a serious threat for penguins and other diving predators of the Southern Ocean.” So while the effects observed in this study were mostly caused by natural temperature oscillations brought on by El Niño/La Niña effects and other climatic variations, climate change will be the major future driver of temperature changes in the region.

The effects for the king penguin, specifically, could be even more severe if the polar front continues moving farther south each year. During the breeding season, king penguins can only spend about 22 days at sea before coming back to relieve their partner and take care of the chicks. So one concern is that the front could move beyond this travel distance. If king penguins, which are relatively stable now, according to Bost, were to decline too drastically, that could also have a major impact on the marine food web in the Southern Ocean, perhaps leading to an overabundance of the small fish that the penguins feed on.

So the study can be seen as an early look into what’s to come for marine animals in the Southern Ocean if sufficient action isn’t taken to halt global warming. As Bost noted, “Long-term studies of at-sea foraging ecology of marine predators are essential to use it as sentinels of short-term and long-term change in the marine environment.”

And if the research is any indication of what might happen, it’s a future that could end up without some of the world’s most recognizable and beloved animals.