Aantalsverloop en verspreiding van de Nachtzwaluw Caprimulgus europaeus in Drenthe over de periode 1950-98

In the 1950s Nightjars were widely distributed in Drenthe. During the 1950s and 1960s many small heaths were transformed into arable land. This loss of suitable habitat resulted locally in the disappearance of Nightjars, especially in the northern part of the province (Figure 1). In 1972 and 1973 two gales wreaked havoc upon conifer plantations, resulting in large clearfellings and the creation of extensive potential Nightjar habitats. Several such clearfellings remained occupied by Nightjars until the early 1980s, when they became unsuitable due to replanting with and ageing of conifers. Settlement at newly created clearfellings coincided with simultaneous declines of numbers at traditional sites on open woodland and on heaths (Figure 2). In the mid-1980s measurements were taken to restore peat moors in the southeastern part of the province. Birch forest was clearfelled before raising the water level. Just in advance of raising the water table, and probably in response of the clearfelling, the local Nightjar population boomed. However, numbers declined again after the area was flooded (Figure 2). This decline had a significant impact on Drenthe's breeding population (Figure 3), as numbers decreased further and breeding sites in the western part of the province were evacuated. Apparently, the gales in 1972 and 1973 (with the creation of many clearfellings in their wake), as well as habitat restoration, only temporarily slowed down the decline started in the 1950s. In the course of the 1990s, numbers increased slightly for no apparent reason.