More than ten years of autonomous acoustic recording of bats’ echolocation calls at an unmanned offshore research platform 45 km north of the island of Borkum (North Sea) were analysed in relation to season, time of day and weather. To our knowledge this is the longest systematic dataset on offshore bat migration worldwide. Three-hundred and seventeen call sequences were recorded during typical migration times in spring and autumn and assigned to at least 23 Nathusius’ pipistrelles (Pipistrellus nathusius), 3 northern bats (Eptesicus nilssonii) and 2 Leisler’s bats (Nyctalus leisleri). Compared to the prevailing wind conditions, more bats than expected were recorded at lower wind speeds and southerly winds. Bats occurred under supporting tailwinds, but also under strong headwinds. In both seasons most bats occurred under winds from the south (i.e. crosswinds), which indicates offshore wind drift. We neither found effects of air pressure, nor of change in air pressure. Most registrations coincided with a dense cover of clouds, fog/low stratus and/or rain. From the structure of echolocation calls it can be concluded that most bats explored the platform rather than just passed it on transfer flights, some even foraged there. We conclude that most of the bats were on migration and attracted by the brightly lit platform and/or sought refuge there. This involves the risk of collisions with offshore wind turbines (which need to be brighter lit at sea than onshore). We assume that a great part of offshore bat migration takes place beyond the range of currently available techniques at greater altitudes than known so far.
Migration Phenology and Behaviour of Bats at a Research Platform in the South-Eastern North Sea
Title: Migration Phenology and Behaviour of Bats at a Research Platform in the South-Eastern North Sea
December 01, 2016
Hüppop, O.; Hill, R. (2016). Migration Phenology and Behaviour of Bats at a Research Platform in the South-Eastern North Sea. Lutra, 59(1-2), 5-22.