As Antarctic temperatures warm, the penguins' main food source is plummeting.
Chinstrap and Adélie penguins have declined by more than 50 percent since 1980.
This is because their main food source -- krill -- have declined by up to 80 percent.
Krill rely on sea ice to reproduce, and sea ice levels have declined dramatically.
Numbers of Chinstrap and Adélie penguins in the Antarctic Peninsula region have dropped by more than 50 percent in the last 30 years, driven mainly by dramatic declines in supplies of tiny, shrimp-like krill, their main prey, says a new study.
Krill, meanwhile, have declined by 40 to 80 percent, due primarily to rapidly warming temperatures in the area -- the South Shetland Islands near the tip of the Antarctic Peninsula and nearby sites.
This is one of the fastest-warming places on the planet with winter mean temperatures some 10 degrees Fahrenheit warmer now than in pre-industrial times.
Researchers previously thought that chinstrap penguins would flourish as temperatures warmed because they winter in the open water near ice edges, unlike Adélie penguins, which winter on pack ice. In earlier years, chinstraps did better in warmer winters, while Adélie penguins grew their numbers in cold winters with lots of ice.