Roofvogeltrek op Cap Bon, Tunesië, in april 1974

In 1974, raptor migration was counted at Cap Bon in Tunisia, the jumpboard for raptors crossing the Central Mediterranean in spring, between 21 and 29 April. This period complements the count, albeit with a 6-day gap, performed by Thiollay (1975) between 26 March and 14 April 1974. In combination with the May-count in 1975 (Thiollay 1977), these three separate efforts cover the better part of the migratory period of a single spring in the mid-1970s. The count by Dejonghe (1980), from 30 April up to and including 16 May 1979, produced another validation for numbers counted in the 1970s (Table 1). A comparison with spring counts in 1990-92 (Kisling et al. 1994) showed steep declines in the numbers of Honey Buzzard Pernis apivorus, Black Kite Milvus migrans, Egyptian Vulture Neophron percnopterus, Short-toed Eagle Circaetus gallicus, Pallid Harrier Circus macrourus, Buzzard Buteo buteo (probably nominate) and Booted Eagle Hieraaetus pennatus. Increases were evident in Marsh Harrier Circus aeruginosus, Sparrowhawk Accipiter nisus and Hobby Falco subbuteo. Montagu’s Harrier Circus pygargus and Long-legged Buzzard Buteo rufinus were more or less stable. Most of these trends reflect real population changes in Europe. However, the decline in passage of Honey Buzzards seems to contradict the supposedly stable European population (BirdLife); however, reliably monitored trends in Europe (Sweden, Finland, Germany) indicate long-term declines, and the decline in Tunisia during spring migration is therefore consistent with a decline on the western and northern breeding grounds. On the other hand, the decline in passage of Common Buzzards contradicts the positive trend in Europe; a similar discrepancy was found at Gibraltar (Bensusan et al. 2007). The tendency of Buzzards to cross the Mediterranean Sea to winter in Africa has presumably declined during the past decades, accounting for the much lower numbers counted at watch sites like Gibraltar and Cap Bon nowadays. A similar trend is visible in Booted Eagles, which increasingly winter in southern Europe.