blotches and other egg markings with visual pattern-recognition abilities to help them reject cuckoos' counterfeit eggs. Most other passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.

However, the photographic markings on passerine eggs have been suggested to reduce brittleness by acting as a solid state lubricant. If insufficient calcium is available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases