Spatial and numerical responses of Red Kites Milvus milvus to the Common Vole Microtus arvalis population outbreak in central Europe

Predator behaviour and population numbers can be determined by many factors such as prey availability, individual and habitat characteristics, and intraspecific or interspecific factors. Using satellite telemetry, we measured home range size in 3 individuals of Red Kites (Milvus milvus) in three consecutive winters to document the pattern of spatial responses to increasing availability of its dominant prey, the Common Vole (Microtus arvalis), in the Břeclav District, Czech Republic. Starting with winter 2017/2018, we found that the home range sizes decreased in winter 2018/2019 when the index of vole population density increased from 678 burrow entrances in autumn 2017 to 1414 burrow entrances per hectare in autumn 2018. Home range sizes did not change in winter 2019/2020 in spite of the further increase in vole population density up to 6673 entrances per hectare in autumn 2019. Based on censuses at 5 communal roosts in January 2018, 2019, and 2020, we documented the pattern of numerical responses to increasing availability of voles. Numbers of wintering Red Kites did not respond to growing vole densities until they reached the highest level in autumn 2019, suggesting that the response of wintering numbers was delayed by 1 year compared to that in home range. Our study thus provides empirical support for the spatial and numerical responses of Red Kites to prey availability and suggest that these responses may differ in sensitivity to increases in vole density, being triggered at different periods of the vole population cycle.