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Résumé :
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Data on the breeding biology and demography of Goshawk and Buzzard have been collected since the years Sixties in the Entre-Sambre-and-Meuse during ringing activities of young birds in the nest. Data gathered since 1980 are analyzed here.The population of controlled Buzzards (approximately 20 breeding pairs on average) underwent cyclic variations of abundance following a 2 to 4 years period but remained stable overall in the long run. After a period of stability and abundance during the early Eighties (average of 15 breeding pairs), then of greater variability and lower abundance, the population of Goshawk fell in a brutal and drastic way after 1996 (average of 2 pairs) (fig. 1). The analysis of the data and the examination of various hypotheses (food or territory competition, contamination by pesticides, sensitivity to various causes, voluntary or not, of accidents) do not allow identifying the cause of these divergent evolutions.
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