Two penguin species are responding differently to rising temperatures in the Antarctic, according to a new study. Gentoo penguin populations have almost tripled in recent years while their habitat partners, chinstrap penguins, struggle to keep up.
Adaptive feeding strategies that in the past decreased competition for food between gentoo and chinstrap penguins are now proving problematic for the chinstraps.
Researchers looked at the stomach contents of breeding adult penguins and collected feathers and eggshells to identify what penguins were feeding their chicks. Digging deep into layers of gravel around penguin nesting sites, the researchers were able to gather information about penguin diets from 40,000 years ago. They also looked at the ear bones of fish eaten by penguins to identify whether the birds were eating nearshore fish or offshore fish.
"Kind of like a teenager, [gentoos] will eat anything," said William Patterson from the University of Saskatchewan. Gentoos adapted to have a flexible and diverse diet, while chinstraps tend to forage farther offshore, seeking more of a specialist diet. For a long time, this allowed the two species to coexist.
"Birds that are specialist eaters are going to be sensitive to change," Patterson added.
Survival gets complicated
In the last 50 years, temperatures in the Antarctic Peninsula have risen by about 5 degrees Fahrenheit. Chinstraps’ main source of food, krill, depends on sea ice for protection from predators. Krill also feed on algae that grow under sea ice, but recent higher temperatures have dramatically reduced the quantities of sea ice and, as a result, the number of krill in the Antarctic.
"The average temperature in winter is no longer below freezing," said Wayne Trivelpiece, a researcher from the Antarctic Ecosystem Research Division of the National Oceanic and Atmospheric Administration. "No one saw this coming — a small temperature change can have a tremendous impact. It’s an instantaneous change — we went from ice to water."
Breeding seasons have also been affected by warming in the Antarctic, and once again, gentoo penguins are better adapted to cope with this change. Gentoo breeding season is much more flexible than chinstrap breeding, increasing the chance that their chicks will survive.
Gentoos also feed their chicks for several more weeks than chinstrap penguins, teaching gentoo chicks how to hunt for food. Chinstrap chicks are often left to learn how to feed on their own, but with less food available, hunting may be a challenge.
The story isn’t over. With temperatures projected to continue rising, Antarctic chinstraps could face more trouble ahead.
"There are still down-the-road [climate] effects that we won’t know until we have to deal with them," Patterson said.