A preliminary inventory of the parti-coloured bat in the Eemshaven – Delfzijl area, Groningen, the Netherlands
Authors: Roel E. Modderman, Raymond C.J.G. Haselager & Jeroen C.S. Creuwels
https://doi.org/10.63269/SJL5812
Abstract: The parti-coloured bat (Vespertilio murinus) has been considered a rare species in the Netherlands, with only one known nursery colony since 1998. A possible second colony was reported in 2002 in the north-eastern part of the province of Groningen, but it was not rediscovered afterwards. In 2016, a first systematic survey on the occurrence of the parti-coloured bat with hand-held and static bat detectors was conducted in the area of Eemshaven–Delfzijl in northeast Groningen. During the inventory, using a hand-held detector, three roosts belonging to two colonies, were found in the villages of Spijk and Bierum. In 2016, the highest number of departing particoloured bats in one night in Spijk was 29 and 12 in Bierum. In 2017 the highest figures were 61 and 12, respectively. Low numbers (1-4 individuals) of serotines (Eptesicus serotinus) were detected departing from the same roosts, always before the parti-coloured bats departed. There were indications of a possible third colony, but these could not be confirmed. We report observations showing that reproduction has taken place in the study area and occurred in or very close to the roosts that we observed. Automatic recorders detected much foraging activity in a relatively small area on the western shore of the river Ems, situated 2.5-4.5 km away from the roosts. During peak activity in this foraging area up to 71 recordings of nyctaloid bats (i.e. belonging to the acoustically similar genera of Nyctalus, Eptesicus or Vespertilio) in one 10-minute interval were recorded. In general, only a small proportion could be identified with certainty and we discuss the difficulties experienced with automatic identification of nyctaloid bat calls. In autumn the study area was surveyed for display calls and courting locations of males, especially in urban areas with high buildings. However, no courting male parti-coloured bats were found. Although the parti-coloured bat mostly lives in houses and buildings, the colonies are probably often overlooked and we suggest that the colonies found in this study have existed for decades.
