Eggshell blue-green colouration fades immediately after oviposition: a cautionary note about measuring natural egg colours

Abstract

The colour fading in eggs of the Pied Flycatcher was studied in Spain. Egg colour for >400 eggs was estimated at the moment of oviposition, at the onset of incubation, and at the end of incubation. Results, obtained using a spectrophotometer, showed that egg colours tended to fade significantly during the study period. For unhatched eggs over lon-ger time periods of 6 and 23 months after incubation, the blue-green colouration faded further still. These figures suggest that studies on egg colouration should account for tem-poral changes in egg colouration.