Penguin colonies in Antarctica have different diets depending on the amount of sea ice surrounding them. Colonies surrounded by sea ice tend to eat more fish, while those in areas with less sea ice rely more on krill—tiny, shrimp-like crustaceans that are a key part of the Antarctic food web. Researchers have found that penguin colonies that consume more fish are more successful at maintaining their population numbers. This information is revealed through the color of penguin poop, or guano, which can be observed from space using satellite imagery. Adélie penguins, one of the most common predators in the Southern Ocean, nest on rocky areas around Antarctica. These birds produce large amounts of guano, especially in colonies with hundreds of thousands of nesting birds. Scientists have used NASA’s Landsat satellites to study these guano deposits, analyzing thousands of satellite images dating back to the 1980s. This research has helped uncover penguin dietary habits and how environmental changes, such as climate change, affect their survival. The color of penguin guano can indicate what they have been eating. Krill have a pinkish exoskeleton that penguins do not fully digest, giving their guano a rosy hue. Researchers developed a quantitative method to link the color of guano to the proportion of krill in a penguin’s diet. Using data from nearly 4,000 satellite images, they found that penguin diets vary across the Antarctic continent, as well as seasonally and from year to year. The data suggests that climate change is altering penguin diets and the broader Antarctic food web. Since the 2010s, sea ice has been declining significantly, which has led to fewer fish in the area. This is bad news for penguins, as chicks that are fed fish tend to be heavier and more likely to survive to adulthood. In areas where penguins eat less fish, their numbers have declined over the past few decades. Meanwhile, colonies that eat more fish are more likely to remain stable or even grow. As sea ice continues to decrease, Adélie penguins are facing increased competition for both fish and krill from other marine animals and human activities, such as fishing trawlers harvesting krill for fish feed and supplements. Improved satellite technology is helping scientists monitor these changes and better understand the impact of environmental shifts on wildlife.