Plotseling zestig Blauwe Kiekendieven Circus cyaneus op slaapplaatsen van het Dwingelderveld en Doldersummerveld in 2006-08
Drentse vogels , Volume 22 - Issue 1 p. 42- 46
(Fig. 2) in the southwestern part of the Province ofDrenthe. Until2005 maximum numbers at both roosts never exceeded 15 birds (Fig. 1, Table 1). In 2006/07 and 2007/08 however numbers suddenly peaked at 35 and 60 individuals, but in 2008/09 the figures were back to normal'. Of 190 identified foraging harriers in 1998-2008, adult males predominated with 33%, adult females and subadult females both 25% and subadult males 17%. Fint arrivals occurred between 9 September and 2 October (mean 20 September) and the birds left the wintering grounds between 8 and 28 April (mean 18 April). The slight increase in the winter population between 1964 and2005/06 (Fig. 1) is in agreement with the increasing numbers found in the national scheme since 1980 (Bode et al. 2008). This was not the case in 2006/07. Then the national index dropped, while the numbers in Drenthe and in an other areas in the eastern part of The Netherlands increased sharply. Numbers in Drenthe did not correlate with weather conditions and were (as far as we know) not related to a local rodent peak.
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Joop Kleine, & Arend J. van Dijk. (2008). Plotseling zestig Blauwe Kiekendieven Circus cyaneus op slaapplaatsen van het Dwingelderveld en Doldersummerveld in 2006-08. Drentse vogels, 22(1), 42–46.
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