Satellite images have been used to track changes in the diet of Adélie penguin colonies, with the color of their droppings offering clues about what they eat. Researchers have noticed that the guano—penguin droppings—of certain colonies turns pink, indicating a shift from a diet rich in fish to one dominated by krill, a tiny cold-water crustacean. This shift in diet has important consequences for the penguins, as chicks fed mainly on krill tend to be lighter and have a lower survival rate into adulthood compared to those fed on fish. Adélie penguins are among the most numerous predators in the Southern Ocean, feeding in the water but nesting on rocky shores around Antarctica. Their large colonies, which can contain hundreds of thousands of nesting birds, produce vast amounts of guano. This guano is easily visible from space, allowing scientists to use NASA’s Landsat satellites to monitor penguin colonies from afar. An interdisciplinary team of researchers used thousands of satellite images dating back to the 1980s to study penguin guano and determine their diet over time. They found that when sea ice is abundant, penguins tend to eat more small fish. However, when sea ice is less common, they rely more heavily on krill. Krill has a pink exoskeleton that penguins do not fully digest, which gives their guano a pinkish color. This coloration allows researchers to determine the penguins’ diet. To confirm the link between guano color and diet, researchers collected guano samples and used a spectrometer to measure the color as a satellite would see it. They also analyzed the guano’s composition to identify the specific food sources. Using data from about 4,000 satellite images, researchers observed that penguins’ diets vary depending on their location in Antarctica, as well as seasonally and from year to year. The data show how climate change is influencing penguin diets and the broader Antarctic ecosystem. Since the 2010s, sea ice in Antarctica has been declining, with several years setting records for the lowest coverage. This decline has led to fewer fish, which is bad news for penguins. Chicks raised on a fish-based diet are generally heavier and have a better chance of surviving to adulthood. In areas where penguins eat less fish, their populations have declined over the past few decades. In contrast, colonies that consume more fish have remained stable or even grown. As sea ice continues to retreat, Adélie penguins face increased competition from other marine animals and human activities for access to fish and krill. For example, baleen whales, which primarily feed on krill, have seen population increases in the Antarctic Peninsula since commercial whaling ended decades ago. Chinstrap penguins, which also eat krill, have expanded their range southward as the climate warms, increasing the number of predators in these waters. Additionally, industrial fishing for krill, used in fish feed and human supplements, adds further pressure on penguin populations. The use of satellite images has allowed researchers to understand how Adélie penguins’ diets vary across different regions, how they change with the seasons, and how they adapt to environmental shifts over time. As satellite technology continues to improve, scientists have new opportunities to monitor wildlife in ways that were previously impossible, providing crucial insights into how the world is changing and how humans might adapt to these changes.