This report is a supporting note to ZDV report no. 2016.031 Migration bats at the southern North Sea.
In recent years, exploratory research into the occurrence of bats at the Dutch North Sea has shown that there is regular seasonal migration over sea of at least Nathusius’ Pipistrelle Pipistrellus nathusii but perhaps also of Parti-coloured Bat Vespertilio murinus and Common Noctule Nyctalus noctula (Boshamer & Bekker 2008; Jonge Poerink et al. 2013; Lagerveld et al. 2014a, 2014b, 2015; Leopold et al. 2014). Given the planned large-scale development of wind farms in the Dutch part of the southern North Sea in the coming years (SER Agreement 2013), the growing evidence that bats are vulnerable to collisions with wind turbine rotor blades and barotrauma caused by the fluctuating air pressure near the blades (e.g. Baerwald et al. 2008, Brinkmann et al. 2011, Bach et al. 2014, Cryan et al. 2014), the Ministry of Economic Affairs commissioned to Rijkswaterstaat (RWS) a two-year monitoring programme in 2015 to determine the occurrence and abundance of bats at the North Sea. This study is currently being conducted in a monitoring project titled 'Research on distribution and behaviour of bats in the southern North Sea' (RWS case number 31103115). It aims at providing insight into bat movements over sea. However, in order to be able to make better estimates of the actual numbers of bats at sea and thus to get a clearer picture of the potential impact of offshore wind energy development on population level, more research is needed into the population ecology of bats in Europe and beyond. It is currently unclear what is the population size of the relevant species, which proportion migrates over sea and which proportion travels over land.