The number of penguins in western Antarctica has halved in the last 30 years, and experts reckon warmer seas could be to blame.
Young penguins like eating krill which are small shrimp-like animals, but rising sea temperatures mean that there's far fewer krill around to eat.
Krill need ice to survive and some scientists think climate change is causing Antarctic ice to melt faster.
With less food, Adelie and chinstrap penguins are struggling to survive.
The study also says the penguins there are having to compete for the krill with more and more whales and fur seals, whose numbers are recovering from being hunted by humans.
The scientists have warned that the trend for fewer krill, and so fewer penguins, will continue if the oceans continue to warm up.