Variation in the diet and breeding biology of the Common Barn-owl (Tyto alba) in a demographic cycle of Common Vole (Microtus arvalis) between two outbreaks^×

In the present study, we analysed the variation of breeding parameters and the diet composition of the Common Barn-owl (Tyto alba) in three different demographic phases of the Common Vole (Microtus arvalis) in a complete population cycle between two outbreaks. The study was conducted in the south-eastern part of the Transdanubian region in South Hungary. For the analysis, we used data of 81 randomly selected first clutches from 2015 to 2019, a time period which represented a full demographic cycle of the Common Vole after the 2014 outbreak with an exceptionally high peak. We tested the impact of prey abundance and diversity of diet composition as continuous predictors as well as the demographic phase of Common Vole and the mesoregion as categorical explanatory variables on the measured reproductive outputs as response variables using Generalized Linear Models (GLM). Considering the breeding parameters, the number of fledglings, and fledging and reproductive success were significantly higher in the increase phase than during the vole crash phase. Based on GLM models, our results demonstrated that the clutch size of the Common Barn-owl is determined ultimately by the availability and consumption rate of the Common Vole as main prey, while other small mammal prey categories did not affect the clutch size. These results support the finding that the clutch size of vole-eating raptors and owls, which begin breeding periods in early spring predicts the vole abundance in this early spring period. Considering the other investigated small mammal prey groups, the alternative prey role was confirmed only in case of the Murid rodent prey categories (Apodemus spp., Muridae).