An aerial photo of a penguin colony on an island off the coast of the Antarctic Peninsula. Penguin guano leaves a clear mark on the landscape. Thomas Sayre-McCord / WHOI / MIT

Penguin colonies are so large that their masses of excrement can be seen from space, offering scientists a useful means of studying the Antarctic birds. An analysis of 30 years of satellite images of penguin guano shows how the birds’ diets are shifting in response to warming.

Penguin droppings not only amass in huge volumes, but also stand out clearly against the white snow blanketing most of Antarctica. In 2024, scientists discovered four new colonies of emperor penguins by scanning satellite imagery for the signature brown streak left by their excrement.

For the new study, scientists analyzed subtle shifts in the color of Adélie penguin guano to track changes in their diet.…