Abstract

The egg of the Common Guillemot Uria aalge is one of the most strikingly beautiful of all British breeding birds. Although colour and patterning are variable, it is typically a vivid blue. Equally striking is its pyriform shape, and the biological significance of this has long been misinterpreted. Traditionally it has been thought that the shape is related mainly to the prevention of the egg from rolling off the often precarious breeding ledges. Here, I bring the story up to date, with current research into, and explanations for, the shape of the Guillemot’s egg.