Seasonal Dynamics of Bat Activity in the Bosphorus Region (Istanbul, Türkiye): Acoustic Evidence for a Potential Migration Corridor Between Europe and Asia

Long-distance migratory bats may face concentrated risks where movements funnel through geographic corridors, yet migration in southeastern Europe remains poorly documented. Istanbul and the Bosphorus are internationally recognized as a major migration bottleneck for birds, but their importance for bats has not been systematically investigated. We used passive acoustic monitoring at four stations along the Bosphorus from April to November 2022 to characterize bat activity and species occurrence, with detailed seasonal and meteorological analyses focused on Pipistrellus pipistrellus, P. nathusii, and the Nyctalus noctula/N. leisleri acoustic group. Across 3613 station-hour observations and 259,654 bat passes, at least twelve species were identified, including the globally Vulnerable N. lasiopterus. Pipistrellus pipistrellus was active throughout most of the season, whereas 84 to 93% of P. nathusii passes occurred after mid-August, peaking synchronously at all four stations between 26 and 29 September. Season-specific wind associations were weak, not supported by cross-validation, and shared by the resident P. pipistrellus, indicating weather effects on local activity rather than directed movement. These patterns are consistent with seasonal bat migration through the Istanbul–Bosphorus region and support the hypothesis that the strait forms a migration corridor, highlighting its potential importance for conservation and wind-energy planning.