Grauwe Kiekendieven Circus pygargus in Nederland in 1996

In 1996, Montagu’s Harriers arrived two weeks later than usual on the breeding sites in The Netherlands. Altogether, the Dutch population comprised of 23 territories, i.e. 4 in De Lauwersmeer, 15 in Groningen (including 3 bigamous males) and 4 in Flevoland (Fig. 1). Mean onset of laying was 30 May (SD=16.1, range = 8-29 May, N=6). Clutch size of completed clutches averaged 3.28 eggs (2x 2,2x 3, 2x 4 and 1x 5 eggs). Mean number of fledglings averaged 2.56 (1x 1, 4x 2, 2x 3 and 2x 4 young). The sex of all nestlings could be established in six nests: 12 males and 6 females. Another nest contained a male and two females; a fourth nestling was too small to be sexed. Nests were built in alfalfa (7x), winter wheat (4x), grass sown for seed production (2x) and herbage (5x). This habitat choice necessitated an intensive cooperation between farmers, harvesters, conservationists, birdwatchers and governmental agencies to ensure safe fledging (see Photos). At and near nests in the province of Groningen, 196 prey remains were found and identified (Appendix 2). Common voles Microtus arvalis still constituted the main prey (as in earlier years, see Fig. 2), despite a vole crash in spring. Passerines are also important prey species, especially Skylarks Alauda arvensis, Meadow Pipits Anthus pratensis, Yellow Wagtails Motacilla flava and Starlings Sturnus vulgaris.