Differences in bat activity in relation to bat detector height: implications for bat surveys at proposed windfarm sites

We recorded bat activity simultaneously at ground level and 30 m height using Anabat II bat detectors and Anabat ZCAIM recording units mounted oil masts at seven sites of varying habitat type in eastern England At the lower detectors 6194 passes were recorded, 90 02% of calls were from Pipistrellus, 691% were from Nyctalus/Eptesicus 1.70% were Myotis/Plecotus. 0.13% were Barbastella and 1 24% could not be determined to species At the higher detectors 484 passes were recorded from Pipistrellus (65 08%) and Nyctalus/Eptestcus (34 09%) and 0 83% were not determined to species Total bat passes and the number of Pipistrellus passes were significantly higher oil the lower detectors compared with the upper detectors The difference between Minibus of passes of significantly upper and lower detectors was not significant, despite proportionally more passes of these species being recorded at height No extra Species groups were recorded at height than were recorded at ground level except at one site where closed canopy broadleaved woodland surrounded the mast Here, Nyctalus/Eptevicits species were recorded only at height Overall, 28% of Nyctalus/Eptesicus passes and 5% of Pipisireflus passes were recorded exclusively at height, and not at ground level Assessing bat activity levels From gound level detectors only can therefore be misleading, particularly when surveying high-flying species that are most likely to be at risk from wind turbine developments