Resultaten van slaapplaatstellingen van blauwe kiekendieven Circus cyaneus in de kustpolders en het krekengebied van NO-Vlaanderen in de winters 1990-1991 en 1991-1992

In January 1989 and 1990 simultaneous Hen Harrier Circus cyaneus roost counts were carried out in the Flemish coastal polders. In the following winters (1990-'91 and 1991-'92), similar counts were organized on five different dates as part of the "Hen Harrier winter Roost Survey" of the BTO IR. Clarke). The polder area of N.E.-Flanders was counted too. This paper provides a brief outline of these censuses. 16 roosts were visited in 1990-'91 and 12 ones in 1991-'92. Among them 10 and 7 ones were at least once occupied. The most important roost is and remains the Blankaart in Woumen. The next important ones are the Zwin in Knokke and the Oostpolder-kreek in Sint-Jan-in-Eremo. The numbers of the Hiddle Coast are traditionally low: only a few scattered specimen staying over in the Rattevalle or the Kleine Keignaert. The total numbers of January 1991 were 53-57. In January 199233-38 specimen were counted. In comparison to the fairly high numbers of the previous winter, 1991-'92 has low ones. The size of wintering Hen Harriers in het Flemish coastal polders can be estimated at 35-100 specimen. To this, one must add the 5-10 ones in the marshland of N.E.-Flanders. These relative high numbers in comparison to results of neighbouring countries, stress the great importance of our polders for Hen Harrier. Further investigation is necessary in order to find a solution for unresolved questions concerning winter distribution of this species and therefore colour-marking study can play a major role.