Hoe lang nog jodelende Wulpen Numenius arquata in Drenthe?

In SW-Drenthe (23.500 ha of which 56% farmland and 10% heath) Curlews have been monitored since 1967. Breeding success was established indirectly by recording the proportion of pairs emitting alarm calls (i.e. with young). During 1967-97 the number of territories fluctuated between 194 and 316, without long-term declines or increases. Short-term declines, as in the mid-1980s, were thought to have resulted from severe winter weather. However, trends were very different between habitats. Numbers in farmland remained more or less stable throughout this period (Fig. 1), whereas numbers on heathland declined steeply from the mid-1980s onwards (Fig. 2). Curlews breeding on heaths are known to forage on nearby farmland, and the changes in numbers may have been partly due to a permanent switch from heath to farmland. Breeding success on heath also showed a significant decline during the 1980s and 1990s; no such decline was apparent in farmland (Fig. 3). It is thought that changes in breeding success are mainly responsible for the dichotomy in trends between heaths and farmland. Poor breeding success on heaths may have been caused by changes in local food supply (impoverished feeding conditions on farmland neighbouring heaths) and predation. Predators have increased since the 1960s, especially Red Fox Vulpes vulpes, corvids and raptors (Fig. 4). However, during the same period Lapwings Vanellus vanellus breeding on heaths have increased in numbers (following habitat management) whereas predators also abound in farmland (where Curlew numbers are stable).