Assessing the Bosphorus as a migratory corridor for Pipistrellus nathusii using acoustic monitoring methods

Abstract

Türkiye has one of the richest bat diversity in the Mediterranean region. However, essential ecological information about bat species, such as population sizes, distributions and their migration behaviour is lacking. This information gap is primarily due to the elusive behavior of bats. Most of the bat research in Türkiye is about cave-dwelling species, which are relatively easier to study. Studies on other species, on the other hand, are generally based on opportunistic and non-systematic surveys. In this context, acoustic ecology methods offer an effective approach to investigating bats. This study aims to conduct a systematic acoustic ecology investigation in İstanbul, Türkiye, with a specific focus on the role of Bosphorus as a migratory corridor for bats. In particular, the migration patterns of Pipistrellus nathusii, a long-distance migratory bat species, were investigated. Additionally, the relationship between bat activity and meteorological parameters, as well as moon phases were explored to assess their impact on migration. Ultrasonic sound recordings were collected from four different locations along the Bosphorus, spanning from north to south, between April and November 2022. Recordings were preliminary analysed with Kaleidoscope Pro software and then processed manually. Analysis revealed that bat activity was positively related to temperature. Wind speed and direction affect bat activity in different ways depending on the season. In particular, light winds are positively associated with bat activity. When the effect of moon phases on bat activity was examined, it was found that the P. nathusii activity level in Yıldız City Park and ITU Campus was more affected by the moon phases, and especially the Nathusius Pipistrelle acoustic group activity decreased during the full moon phase. Pipistrellus nathusii activity in Yıldız City Park increased from mid-August and decreased towards the end of October. Activity on the ITU Campus started to increase in mid-August, peaked towards the end of September, and decreased at the end of October. Activity in the Atatürk City Forest started to increase in mid-August, peaked in September, and continued to decrease slightly in the autumn. In the Sarıyer Forest, there was an increase in August, the highest activity was seen in September and decreased with the end of the autumn. These findings show that the Bosphorus is a migratory corridor for P. nathusii. The insights gained from this study will contribute to the conservation of migratory bat routes between Europe and Asia.