Protoporphyrin

Protoporphyrins are tetrapyrroles containing the following side chains:


 * methyl (4)
 * propionic acid (2)
 * vinyl (2)

Protoporphyrins are deposited in the shells of the eggs of some birds as a brown or red pigment, either as a ground colour or as spotting. This occurs in most passerine species, some ground-nesting non-passerines, such as waders, gulls, nightjars and sandgrouse, where it provides camouflage, and some parasitic cuckoos, which need to mimic their passerine hosts' eggs.

Protoporphyrins strengthen the egg shell, and are deposited where the shell is too thin as a result of calcium shortage. Spotting therefore tend to be heavier where the local soil is calcium-deficient, and in the eggs laid last in a clutch.