Kestrel (Falco tinnunculus) Science Article 5
1) Offspring sex ratio may be an unpredictable component of life history that might select for behavioural plasticity in parental care. If the parents do not have such plasticity and the two sexes of offspring differ in size, individuals in a brood or litter biased towards the larger sex offspring may suffer from food shortage. Sibling sex ratio could also affect the young through asymmetric sex-related sibling competition. 2) We created single-sex broods of sexually size-dimorphic Eurasian kestrels (Falco tinnunculus L.) with mixed-sex control broods in order to test whether parents have behavioural plasticity to respond to the sex ratio of their brood and whether smaller male chicks suffer from reduced health status because their larger female siblings outrival them in sibling competition. The experiment was conducted during two years (2000 and 2001) that differed in the abundance of voles, the main natural prey of kestrels. […].
Laaksonen, T., Fargallo, J. A., Korpimaki, E., Lyytinen, S., Valkama, J. & Poyri, V. 2004, Journal of Animal Ecology 73: 342-352