Het belang van een nestcontrole tussen ringen en uitvliegen van roofvogels

The number of nestlings during ringing is normally taken as the number of fledglings in raptors. This validity of this procedure is tested for six species of raptors in western Drenthe, The Netherlands. All nests were regularly checked between ringing and fledging (Table 1). Only in the Goshawk no losses occurrcd between ringing and fledging, All other species showed a discrepancy between ringed total and number of fledglings, especially Kestrel, Sparrowhawk and Hobby (but notice small sample size in Honey Buzzard, Kestrel and Hobby). Losses were particularly pronounced in the small raptor species. These were mainly caused by Goshawk predation. Disappearance of nestlings of Common Buzzards was due to food stress, resulting in the death of one or two of the smallest nestlings. Given these results, an extra nest visit between ringing and fledging is obligatory if breeding success is being monitored.