Wespendieven Pernis apivorus in Sleeswijk-Holstein: een historisch overzicht

Based on the author’s field observations, mostly since the early 1950s in several regions in Schleswig-Holstein in northern Germany (but starting in eastern Germany in 1950), and a survey of the avifaunistic literature, the distribution and abundance of Honey-buzzards in Schleswig-Holstein, and changes therein, are outlined for the past century and a half. In the late 19th century, the Honey-buzzard was considered, by Rohweder, a scarce breeding bird in woodlands in the central and southern parts of Schleswig, but mostly absent from the intensively farmed eastern regions. Quantitative information was largely lacking, but surveys since then have confirmed relatively high densities in central Schleswig-Holstein, where sandy soils permit high densities of social wasps and reptiles) and in southeastern Schleswig-Holstein (not well known in Rohweder’s days because of inaccessibility, but now found to harbour a high density, especially in the duchy of Lauenburg). The coastal regions are largely devoid of Honey-buzzards (maritime influences, intensively farmed) except for the large forests on old sandy soils west of the July isotherm (Husum, Dithmarschen). Changes in this pattern of the past century were partly effort-related, some regions being intensively studied whereas others were hardly visited or intermittently only. The species may not have been affected by shooting and poisoning, contrary to Whitetailed Eagle Haliaeetus albicilla, Red Kite Milvus milvus and other raptor species. An extraordinary case of heavy moult in late June, involving at least four rectrices and four secondaries in an adult female Honey-buzzard in the exceptionally dry summer of 1959, is tentatively attributed to secondary poisoning, as disordered moult was also recorded in Red Kites and Black Kites M. migrans affected by parathion. A larger impact on population numbers and breeding performance is attributed to changes in farming practices, notably the removal and trimming of hedges (used to be preferred habitat for social wasps) and the large-scale conversion of ‘permanent’ grassland into maize (for biogas production), again negatively impacting wasp populations. Local studies, notably by H.D. Martens in the Danischer Wohld/RD near Kiel and by H.-J. Raddatz in the Barmstedter Geest (north of Hamburg), indicate stable populations up to the mid-1990s, then a steady decline. In line with these findings, the author also less frequently encounters moulted feathers of Honey-buzzards and depredated nests of wasps during fieldwork. The above-mentioned changes in the landscape may lie at the heart of this trend, but intraguild predation (especially by Goshawk Accipiter gentilis) may also play a role. In its turn, the latter species may increasingly find its Nemesis in the Eagle Owl Bubo bubo, a top predator which reaches a high density in present-day Schleswig-Holstein. Whether killing Goshawks by Eagle Owls results in less predation of Honey-buzzards by Goshawks remains to be seen.