Climate forces penguin populations into a dive

Ice-loving Adélie penguins, once thought to be more at risk than ice-avoiding chinstrap penguins but actually faring better as the climate changes, in Admiralty Bay, Antarctica. Credit: Lenfest Ocean Program

Dwindling food supplies, caused by climate change, are threatening two species of penguin. Adélie and chinstrap penguins are both suffering thanks to falling availability of tiny shrimp-like crustaceans called krill that they eat. This is contrary to previous predictions, explained George Watters, director of the US National Oceanic and Atmospheric Administration (NOAA)’s Antarctic Ecosystem Research Division. That’s because those predictions directly link the amount of sea ice cover to the number of penguins.

“The prevailing ‘sea-ice hypothesis’ would say that chinstrap penguins might be expected to benefit from climate change because they are “ice-avoiding” penguins,” Watters told Simple Climate. By contrast, “ice-loving” Adélie penguin populations had been expected to fall as the planet warms and ice cover decreases. “But we’re showing that in fact the populations of both species are declining,” Watters said. “We think that the the availability of krill is governing the decline of both animals.”

The sea-ice theory developed from some of the earliest penguin population studies in the 1970s and 1980s, showing that Chinstrap penguin populations were increasing as Adélie penguins decreased. The team that did that work included Wayne Trivelpiece, lead author of the Proceedings of the National Academy of Sciences USA paper published on Monday that now shows both species are in decline. Both studies involved extensive fieldwork in the world’s coldest continent. “Wayne has been going since the Antarctic was invented,” Watters joked.

Husband and wife reunion

The field camps the researchers use to study penguin populations are in the Western Antarctic Peninsula, one of the fastest warming areas on the planet, with 5–6 °C increases in mean winter air temperatures since 1980 and associated decreases in winter sea-ice cover. Credit: Lenfest Ocean Program

The NOAA team surveys penguin populations from field camps at Cape Shireff and Admiralty Bay in the South Shetland Islands region of Antarctica. “It’s an ongoing long-term monitoring effort, a lot of really detailed work we do to study penguins that involves counting, weighing and tagging birds,” Watters explained. Also among the team doing this is Susan Trivelpiece, Wayne’s wife, who spends approximately half the annual October-March study period in Antarctica, rotating with her husband. “Usually Sue goes in first,” said Watters. “She comes out around Thanksgiving time and then Wayne goes in.” As I interviewed Watters the couple were departing for a long weekend reunion at the end of another year’s separation.

As well as their own detailed records, the NOAA scientists also called on population studies made by other researchers who visited penguin habitats at a wider range of locations. “The other kind of study, the way a lot of those work is somebody can get to a colony once and count the birds there, then go back after some period of time and recount them” Watters said. With some colonies boasting populations in the millions, the counting process isn’t necessarily simple. “If it’s small enough, you break it up into grid lines visually and just count the birds,” Watters said. “Another way is with aerial photography.” A third option is to walk around the edge of the colony with a GPS receiver to determine its size, Watters added. Then a scientist can work out how many birds are typically in a given area, and then multiply that by the size of the whole colony.

Reversal of fortune

Watters, the Trivelpieces and their colleagues combined these studies with measures of krill abundance, air temperature changes and sea-ice levels in the region since the 1970s to explore the relationship between these factors and penguin abundance. These revealed that the availability of krill – the penguins’ main food source – could influence penguin populations more directly than access to sea-ice. That means that both penguin species would suffer as sea-ice disappears, because krill need it to reproduce successfully. Overall, the studies showed that rather than growing as had been predicted, populations of chinstrap penguins were less than half their 1977 levels. The situation is therefore “particularly critical” for them, the team say, as they haven’t been seen to adapt to other locations. Consequently the team recommend that the International Union for the Conservation of Nature consider putting chinstraps higher on their “at risk” Red List.

Warming air temperatures and shrinking winter ice extent have led to declines in krill populations and in turn to shrinking penguin populations. Credit: Lenfest Ocean Program

This Adélie penguin colony in Admiralty Bay is shrinking, although Adélie colonies in other parts of Antarctica are growing, but the same cannot be said for "ice-avoiding" chinstrap penguins. Credit: Lenbest Ocean Program

While Adélie penguins had suffered a similar fate in the rapidly-warming West Antarctic Peninsula, climate change has helped them elsewhere. “Adélie populations in the Ross Sea area are actually growing right now,” Watters explained, although he warned that they may ultimately have problems if the ice is not where they need to feed in winter. “In Antarctica, climate change is supposed to play out so that you’ll have more ice in some areas and less in other areas. The Ross Sea is an area where you’re going to have more ice and possibly as a result of that better production of krill, so Adélie penguins are doing well there for now.”