Resultaten van de midwinter-telling 1990 op slaapplaatsen van de blauwe kiekendief <i>Circus cyaneus</i> in de Vlaamse kustpolders

As a part of an international study on wintering Hen Harriers Circus cyaneus in Europe, roosting sites in the coastal Polders of Flanders have been counted on 13 and 14 January 1990. The position of the roosts is given in Fig. I. The numeric distribution on mid-January counts in 1989 and 1990 is shown in Fig. 2. The total number of birds counted was 48-53 (see Table I). We assume however that there are still some (small) unknown roosts (especially in the western part of the Polders). So the real winter population was probably slightly higher (55-65 birds). A similar survey in January 1989 revealed a considerably lower number (40-45 birds) but this was partially due to an incomplete coverage. Some roosts in the western part of the Polders, especially in or near the flood plains of the river Yzer, held a considerable higher proportion of grey males than in the east. This difference in sex-ratio can probably be described to variation in habitat and food supply