The Marsh Harriers breeding in the central part of the province of Friesland, a lowlying peat district with many lakes and extensive reedbeds, are being monitored since 1998-99. Nests are located, clutch and brood size established, chicks measured, weighed and ringed and breeding success recorded. Recently, the local population shows a slight decline: 16-23 pairs/year in 1998-2002, 14-15 pairs/year in 2003-05 (Fig. 1). Breeding performance is also showing a downward trend, particularly in 2003-05 (Table 1): clutch size and brood size declined and egg laying is being delayed. Whereas normally 40-55 chicks were ringed annually, only 20 chicks reached ringing age in 2005. Many nests failed under circumspect circumstances, among which a nest where 5 chicks had been killed by severing their heads. Although persecution is locally rampant, it is not clear whether this is (exclusively) responsible for the local decline, as a declining food supply in this farmland region may play a role as well. On 1 July, a bedraggled adult female was captured on her nest; she was unable to fly following heavy downpours in the preceding night (when she apparently had been protecting her 27-30 day old chicks from soaking). Body mass and wing length closely matched measurements taken from females in other parts of the range (Table 2).

De Takkeling

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Werkgroep Roofvogels Nederland

Romke Kleefstra, & Jan Kleefstra. (2005). Toevallige vangst van adult vrouwtje Bruine Kiekendief Circus aeruginosus als verrassing in teleurstellend kiekenseizoen. De Takkeling, 13(3), 178–184.