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 atterns 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 – a 1-degree Celsius increase in sea-surface temperature caused the front to move south by 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.The research suggests that having to travel so much farther on these foraging trips could have damaging effects on the king penguin population.

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