Abstract: This paper describes the trend of bats hibernating in marl quarries in the south of Limburg, the Netherlands, since 1986 and puts it into perspective by comparing it with the trend between 1940 and 1980, as described earlier by Daan (1980).

Abstract: Hibernation site selection by bats depends on various environmental and physiological factors, microclimatic conditions, and species-specific requirements. For successful overwinter survival, efficient use of stored fat reserves is crucial.

Abstract: The Dutch dune areas between Zandvoort and Bergen aan Zee contain various sites, such as bunkers and ice cellars, in which bats hibernate. The bats in these sites are counted annually each winter.

The winter of 2021 was a special anniversary for bat counts in hibernacula in the Netherlands.

Abstract: Twenty six different marl quarries in Flanders are checked annually for hibernating bats, 18 in the Meuse basin and eight in the Scheldt basin.

Abstract: Hibernating bats along the coast of the Dutch provinces of Noord-Holland, Zuid-Holland and Zeeland are described from the first counts in the early 1960s until the winter of 2020, with an emphasis on trends since 1990.