Grauwe Kiekendieven Circus pygargus in Nederland in 2003

The year 2003 was an average breeding season for Montagu’s Harriers in The Netherlands, with 35 pairs distributed over three breeding localities (Figs. 1 and 2), i.e. Groningen (mainly Oldambt: 27 pairs), Lauwersmeer (3) and Zuidelijk Flevoland (5). Mean onset of laying varied from 22 May in Flevoland, to 23 May in Lauwersmeer and 26 May in Groningen. Clutch size averaged 3.58 eggs, and the mean number of fledglings per successful pair was 2.57. Only 50% of the pairs was successful in raising at least one chick. Most pairs nested in cereals and alfalfa, and had to be protected from harvesting. Main food, as evident from pluckings, pellets and prey remains collected at nests, consisted of common voles Microtus arvalis and a quartet of passerines Alauda arvensis, Anthus pratensis, Motacilla flava, Sturnus vulgaris) but with a scattering of other prey species (including Crex crex). It is estimated that food-supply in 2003 was below-average, especially regarding common voles (poor numbers captured in April). In 2003 much effort was put into tracking radio-tagged birds, among which a bigamous male in its 11 th calender-year (the oldest known in the Dutch ringing scheme). Resightings and recaptures of (colour-)ringed birds shed light on natal philopatry, age of breeding birds, length of foraging flights, habitat preferences (hunting on sandy soils rather than clay, in concert with higher densities of passerines and quail on the first) and displacements after disturbance of first nesting attempts (over several km). In cooperation with German raptorphiles and farmers, Montagu’s Harriers nesting in breeding areas adjacent to the Dutch ones (i.e. in Niedersachsen) were also studied and colour-ringed (for further information; www.grauwekiekendief.nl).