Roepactiviteit van een paartje Bosuil Strix aluco

During April 1992 through October 1994, unpremeditated vocal activity of a pair of Tawny Owls was registered. This pair occupied a territory at Berkenheuvel (province of Drenthe), where the density of Tawny Owls is low. Male and female were vocally least active during May, June and July (August), i.e. the period in which their fledglings were still dependent on food brought by their parents (Fig. 1). Use of the advertisement-call was especially pronounced in late summer (coinciding with eviction of young from territory). The period of constant begging of fledglings covered 20 and 25 days in resp. 1993 and 1994 (the latter year poor in food supply). The bubbling-call was given by both sexes and was heard exclusively between 26 June and 3 December (June lx, July 3x, August 3x, September 7x, October 3x, December 2x). Most advertisement calling took place in late evening and early morning (Fig. 2), but my coverage of midnight hours was poor.