Female-dependent factors affect sex allocation in Lesser Kestrels Falco naumanni

The sex ratio of nestlings is a crucial population determinant in rare and/or endangered species. We investigated the role of female body condition and female-related traits in Lesser Kestrel (Falco naumanni) nestling sex allocation at a nest-box colony in central Greece. We used the total clutch volume and size, female weight, hatching dates, body length, wing length, tail length, tarsometatarsus, and bill length as explanatory variables of the number of male nestlings (the response variable) using CART model analysis. This analysis showed that the reproduction output was biased towards male nestlings when female parents were shorter in body length and clutch size and volume were smaller. The skewed sex ratio favoring females, 1:2.35, suggests that when female parents are in good condition, they invest most in good-quality female nestlings, providing a reproductive advantage and increased long-term fitness.