While rare, a few birds we studied were rule-breakers. One such rule-breaker is the Eurasian spoonbill, whose highly specialised beak shape helps it sift through the mud to capture aquatic life.

Bird beaks come in almost every shape and size—from the straw-like beak of a hummingbird to the slicing, knife-like beak of an eagle. We have found, however, that this incredible diversity is ...