Sex-biased survival of nestlings under unfavourable conditions drives secondary sex ratio in little owls (Athene noctua)

Identifying variation in key life history traits is crucial to predict population dynamics of endangered species. An increased bias in sex ratio as a result of low habitat quality can reinforce population decline and drive small populations to extinction. This is particularly true for monogamous bird species such as the little owl (Athene noctua). However, the underlying mechanisms driving biased sex ratios often remain elusive. Using a robust sample of molecular sex determination data recorded at two nest visits within each of 247 broods we examined the development in brood sex ratio, sexual size dimorphism and factors affecting the survival of little owl nestlings. Brood sex ratio in litt…