Het broedbestand van de Blauwe Reiger Ardea cinerea in Drenthe in 1988-96

Heronries in the province of Drenthe have been censused since 1970. This paper provides an update, covering the period of 1988-96 (and partly 1997, cf. Appendix 1). For the first time since 1970, the number of Grey Herons exceeded 400 nests, probably following a series of very mild winters (1988-90, see frost index in Table 1). The number of breeding birds more than halved after the severe winter of 1995/96 (Table 1), which was evident in the disappearance of small colonies (less than 10 nests) and a decline in number of nests in larger colonies. Most colonies are situated on higher ground along valleys, especially on the so-called Hondsrug in the eastern part of the province.