The eagle owl is the world’s largest and is found in mountains and hilly forests throughout Europe and Asia. As breeding pairs prepare to raise a brood of chicks, various landmarks around their nest become streaked with brilliantly white marks that are noticeable from some distance away. Some of these are streaks of droppings (“faecal posts”) and others are collections of matted feathers, plucked from dead birds (“plucking sites”).

Through a series of clever observations, Penteriani and Delgado showed that these streaks are the equivalent of owl police-tape, delineating the borders of their territory and acting as clear keep-out signs to other owls.

For a start, both faeces and feathers turned up at the highest and most visible points of the