Female condition, egg shape and hatchability: A study on the grey partridge

Egg features are key components of egg quality that can influence future prospects of survival. Past studies have outlined the importance of egg size, but little is known about egg shape variation, differences among females, influence of external factors on shape and the importance of shape for hatchability. In this study of the grey partridge Perdix perdix, we examined shape characteristics (elongation and three indices derived from photographs). There was a significant individual difference in egg shape among females, and shape was influenced by the position in the laying order, with last-laid eggs being less elongated. Egg shape indices were not influenced by food quality (experiment with two diets differing in β-carotene content), nor by an immune challenge (experiment with two groups differing in Newcastle disease virus vaccine treatment). Eggs laid by females in poorer health conditions were more asymmetric and more pointed. Egg hatchability was higher for intermediate egg elongation values.