| Abstract: | We examined inter-clutch egg size variation of Eurasian kestrels Falco tinnunculus in western Finland over a period of 12 years, during which their main prey, Microtus voles, fluctuated in three-year population cycles. Females that bred twice in the area had highly repeatable egg size, and the main part of the observed variation was likely to be due to among-female differences. Laying date also explained some variation in egg size, but compared to the variation between individuals its effect was small and varied among the phases of the vole cycle. During decrease phases and years with low vole abundance mean egg size of clutches declined with laying date, whereas during increase phases mean egg size remained stable within the season. Although egg size was not related to fledging success, we found that egg size may have value for the development of eggs as the probability of total hatching success of a clutch increased with increasing mean egg size. |
