Egg size and shape variation in Rufous Bush Chats Cercotrichas galactotes breeding in date palm plantations: hatching success increases with egg elongation

In oviparous taxa such as birds, clutch characteristics (e.g. egg size, egg mass and the number of eggs) can be considered as energetic investment in reproduction. In this paper, we study variation in the principal component indices of egg size and shape in Rufous Bush Chats (Cercotrichas galactotes) breeding in date palm plantations in the Al Amri Oasis, north Algeria, in 2008-2009 and 2011-2013. For descriptive and comparative purposes, we also present characteristics of egg length, breadth, volume, shape and mass. The size and shape indices as well as dimensions and masses of the eggs laid by particular females tended to be similar to one another, with most variation occurring between clutches (significant repeatabilities for all egg traits). Variation in the size of eggs was influenced by the year-laying date interaction, while variation in the shape (elongation) of eggs was marginally significantly affected by the year-laying date interaction. Year had a significant factor effect on the size of eggs. We also found that hatching success was affected by interactions between year and egg size and shape principal components, thus confirming the existence of fitness-related consequences of variation in the traits of Rufous Bush Chat eggs. Notably, we found that in some years hatching success increased with the elongation of eggs.