In summer 2002, some 270 hours were spent in observing European Honey-buzzards on the Utrechtse Heuvelrug between Amerongen (52°00’N, 52°7’E) and Elst (51°59’N, 5°30’E), a forested region interspersed with small-scale farmland and small towns. Based on descriptions of plumage and stage of moult, four adults consisting of two pairs could be individually recognised. A female was discovered near a partly excavated, but not yet depredated, wasp nest on 27 July: between 16.39 h and 20.41 h the entrance was enlarged from a width of 15 cm (depth 20 cm) to a width of 20 cm. Three combs (2 with diameters of 11 and 15 cm) were eventually emptied in front of the entrance. European Honey-buzzards reacted strongly on playing tape-recorded main calls, both vocally (apparently answering) as physically (approaching the source of the sound and circling overhead). In one case, on 2 August, at least 7 Honey-buzzards (including a bird of unknown identity) eventually flocked around the recorder, circling and calling incessantly.