Seasonal Acoustic Monitoring of Bat Activity from the Northern Marmara Coast, Türkiye: Insights into Autumn Migration and Conservation Implications

Migratory bats face increasing risks from habitat fragmentation, artificial light, and the expansion of wind energy infrastructure, yet their migration patterns remain poorly documented in many regions, including Türkiye. This study presents the results of seasonal acoustic monitoring conducted at a coastal site on the northern shore of the Sea of Marmara, a potential migratory corridor between Europe and Asia. Using a passive ultrasonic detector, bat activity across 18 nights in summer, autumn, and winter 2020 was recorded and analyzed for species-specific activity levels through count-per-minute values. A total of 18.937 bat passes were detected, representing at least six species, including Myotis sp., Eptesicus serotinus, Pipistrellus pipistrellus, P. nathusii, Nyctalus noctula, and Plecotus sp. P. pipistrellus was the most consistently active species year-round, while P. nathusii exhibited a pronounced activity peak during September and October, consistent with autumn migratory behavior documented in other parts of Europe. While acoustic misclassification with P. kuhlii cannot be entirely excluded, the seasonally restricted spike and carcass records from regional wind farms strengthen the identification of P. nathusii as a migratory species in the area. N. noctula and E. serotinus were also detected almost exclusively during autumn, likely indicating their migratory movements through the region. These findings underscore the importance of structured, seasonal monitoring to detect migratory activity and support conservation planning. Given the proximity of the site to the proposed offshore wind developments, the results highlight the need for broader spatial monitoring and improved integration of bat migration into environmental impact assessments in Türkiye.