Abstract
Scientific review summarising information about colouration of avian eggs. Avian eggshell colour and spotting pattern may differ a lot.
Big differences exist among species, but there also is a huge intraspecific and even intraclutch variation. Proximate causes of eggshell patterning are biliverdin and protoporphyrin pigments, combinations of which create different colours.
The ancestral eggshell was probably white and immaculate but several ultimate causes have led to different eggshell colours during evolution. The necessity to prevent predation was presumably the primary cause for different cryptic colours.
Arms races between brood parasites and their hosts also probably played an important role in the evolution of egg coloration. Moreover, eggshell pigments may improve the thermoregulation of eggs or compensate thinner areas of the shell caused by calcium deficiency.
The blue-green coloration of eggs has been suggested to constitute a sexually selected female signal - the intensity of colour would reflect the physiological condition of the female, and hence it might affect the allocation of male parental care. Some studies document effects of environmental conditions and stress on avian egg coloration.
As egg colour and patterning offers interesting evolutionary interpretations, it has attracted attention of many investigators. Modern methods such as image analysis or spectrophotometry are commonly used when studying egg coloration.
They help to overcome the differences in perception of colours between birds and humans.