Distribution, abundance and reproductive success of the Saker Falcon in Slovakia in 1976–2022

Between 1976 and 2022, we monitored the distribution of nest sites across two habitats of the Saker Falcon (Falco cherrug), nesting in both the mountains and lowlands of Western and Eastern Slovakia. In Western Slovakia, we observed nesting in 79 known nest sites, accounting for 703 nesting attempts, while in Eastern Slovakia, we monitored 281 nesting attempts in 32 nest sites. The brood size varied between these regions; pairs in Western Slovakia produced an average of 3.0 nestlings, whereas those in Eastern Slovakia produced an average of 2.5 nestlings per successful nest. Throughout the period from 1976 to 2022, a total of 2,468 young Saker Falcons fledged in Slovakia. During this period, the range of breeding population gradually shifted to the lowland from the mountains. In the new, predominantly agricultural environment, the nesting success significantly increased from 57.1% in the mountains to 81.1% in the lowland. In Western Slovakia, the benefits of shift in habitat were further justified by the observation that the mean brood size per all breeding attempts in the lowlands was consistently above two young per brood most of the time. In contrast, pairs breeding in the mountains frequently produced two or fewer young per all breeding attempts. Additionally, our findings indicate that electrocution on mid-voltage (22 kV) power lines is the primary cause of mortality among Sakers in Slovakia, with collisions being the second leading cause.