Snelle en massale doortrek van Wespendieven Pernis apivorus op 22-24 augustus 2007

On a migration lookout in the southeastern Netherlands, 22 August 2007 started overcast with lots of rain and a stiff NE wind (5-6 B). The weather improved somewhat in the afternoon (still overcast) when the rain abaited and the wind shifted to ENE and slackened to 4-5B. Counting started at 13.30 h, but only after 15.00 h (and especially around 16.00 h) did Honey-buzzards pass in large numbers. Between 13.30 and 19.00 ha total of 252 Honey-buzzards was recorded at this lookout. For the entire Netherlands, numbers on 22-24 August at migration lookouts amounted respectively to 458, 714 and 527 passage migrants (Table 1). The peak migration in The Netherlands was not preceded by a similar peak at Falsterbo in southern Sweden (Sweden is the most likely origin of passage migrants in The Netherlands), presumably because large numbers made the passage to Denmark to the west of Falsterbo following stiff northeasterlies (Table 2). Apart from over 1200 migrants between 25 August and 5 September 1958 (then identified as Buzzards Buteo buteo and Marsh Harriers Circus aeruginosus, but presumably having mostly involved Honey-buzzards), the above numbers are unprecedented in The Netherlands. The advanced timing of passage, as compared with the usual passage peak between late August and mid-September, may have been indicative of poor breeding success in Sweden, as indeed recorded for Dalsland (http://web.telia.com/~u32023468/index.html.