Postduifringen als indicator voor vroegere nestbezetting door Accipiter gentilis: Over de archeologie van Treekse havikshorsten

By systematically collecting rings of racing pigeons underneath old raptor nests, it was feasible to reconstruct the history of occupation in past years. Pigeon rings contain -apart from an individual code- information on land of origin and year of birth. It was therefore relatively easy to find out in what years the nest had been used by a Goshawk (regarding the fact that 70-80% of the racing pigeons taken by Goshawks are juveniles), to show shifts from one nest to another, to delineate separate territories on the basis of synchronously occupied nests, and to reconstruct the population trend in past decade (Tables 1 and 2). The reliability of this method depends on the collection of all rings underneath nests (use of metal detector is obligatory), a sufficiently large sample of rings per nest (single rings cannot be used), the mapping of all old large raptor nests in the study area, and information from pigeon fanciers when their birds were lost. A comparison of the ring-method with standardized territory mapping revealed an almost identical pattern.