Overwinterende Slechtvalken Falco peregrinus in Zierikzee

The unfinished Gothic tower ‘Dikke Toren’ in Zierikzee (56 m high) in the province of Zeeland (southwestern part of The Netherlands) used to be a regular wintering site of Peregine Falcons, with observations throughout the 1950s. Wintering Peregrine Falcons became extremely scarce from the 1960s onwards. Apart from an observation in 1985, it lasted till December 1998 before another Peregrine Falcon was observed near the church tower. From January through early April 1999, an adult (presumably female) Peregrine Falcon was using the Dikke Toren as resting and feeding site. Pluckings, prey remains and intact prey (probably from a larder) were collected underneath the tower on a regular basis. The bird mainly captured teal, waders and feral pigeons (Table 1); hunting grounds were probably some 1.5 km away to the west of the town. In the winter of 1999/2000 an adult male Peregrine used the same church tower as roosting site. Again, teal and waders were important prey species (Table 1). This bird may also have hunted in tidal areas some 4 km northeast of Zierikzee (seen returning from this direction, without prey). Based on average prey weights and a 15% loss per prey (undigestible parts), it is calculated that both birds had a minimum net consumption of respectively 85 and 70 g. This does not suffice to cover daily energy expenditure, and it is therefore thought that both birds must have had other (undetected) roosting and feeding sites.