Cabezas-Díaz S. & Virgós E. (2007) Adaptive and non-adaptive explanations for hatching failure in eggs of the Red-legged Partridge Alectoris rufa. ARDEA 95 (1): 55-63

Hatching success has been considered one of the main factors associated with fitness in birds. Hatching failure could be the result of two independent events, infertility and death of embryos, which have not been independently considered in most studies. Our study analyses hatching failure pattern in a precocial bird, the Red-legged Partridge Alectoris rufa. In trials with captive birds, we tested effects of egg size, laying order and clutch size on infertility and embryo death controlling for maternal condition and age. On the basis of previous studies we predicted that lighter eggs show higher rates of infertility and/or embryo mortality. We also predicted that infertility prevails in first and last-laid eggs. Infertility represented the most important component of hatching failure in Red-legged Partridge. The importance of egg size in determining hatching success was supported because infertile eggs were lighter than fertile ones. Infertility prevailed in first seven eggs of the sequence of laying supporting previous findings. Hatched and unhatched fertile eggs showed similar weights, but embryo mortality increased with the sequence of laying. Clutch size and maternal body condition did not account for differences in infertility or embryo mortality. We suggest that infertility and embryo death might be caused by physiological constraints on both parents.