Two of the most well-known penguin species in Antarctica — chinstraps and Adelies — are under pressure because a warmer climate has cut deeply into their main food source, shrimp-like creatures called krill.

Fewer of the juvenile penguins survive what scientists call their “transition to independence” because there isn’t enough krill to go around, according to a study published on Monday in the Proceedings of the National Academic of Sciences.

The study found only 10 percent of young penguins survive the first independent trip back to their colonies from their winter habitat, said lead author Wayne Trivelpiece, a sea bird expert at the National Oceanic and Atmospheric Administration’s Antarctic Ecosystem Research Division.

When the study began, back in the mid-1970s, the chances that a two-to-four-year-old penguin would survive the trip was about 50 percent, Trivelpiece said in a telephone interview.