Large‐scale spatial dynamics of vole populations in Finland revealed by the breeding success of vole‐eating avian predators

Summary1 Voles in northern Europe have been shown to exhibit cyclic population dynamics, with a latitudinal gradient in cycle length, amplitude and interspecific synchrony. 2 Previous studies have been based on a relatively sparse network of sampling sites. In the absence of spatially comprehensive long‐term records of vole dynamics, we analysed a proxy of vole density, bird‐ringing data on vole‐eating avian predators, Tengmalm's owl ( Aegolius funereus L.), the Ural owl ( Strix uralensis Pall.), the long‐eared owl ( Asio otus L.) and the rough‐legged buzzard ( Buteo lagopus Pontoppidan) to study spatial population dynamics of voles. 3 We demonstrate that the breeding success of the avian predators is highly dependent on the abundance of voles, which is also reflected in the numbers of nestlings ringed in a particular area in each year. 4 Our results show the expected increase in cycle length from south to north in Finland, but also from west to east, and in contrast to previous studies, increasing irregularity of the cyclic dynamics towards the north. 5 Fluctuations of vole populations have been synchronous over large distances, up to several hundred kilometres. Such large‐scale synchrony is more likely to be caused by movements of vole‐eating predators and/or by climatic perturbations than by dispersal of voles. 6 We could not conclusively verify the recent suggestion that vole population dynamics have become less regular across Finland, although certain long‐term changes are apparent.