Aves, p�le ornithologique de Natagora

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Aves, 28/4 | 1991 | 169-188

  Exceptionally high breeding figures for the Long-eared Owl (Asio otus) and the Kestrel (Falco tinnunculus) in 1991 in the Forêt de Soignes (Belgium).
De Wavrin, H., Walravens, M. & Rabosee, D.

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Article summary

In 1991, exceptional high numbers of Long-eared Owl and Kestrel bred in the Forêt de Soignes, an extensive beech forest to the south-east of Brussels. Taking into account only the Brussels region's part of this forest, 65 Long-eared Owl pairs (density: 3.92/km2) and 18 to 21 Kestrel pairs (density: 1.09 to 1.27/km2) were recorded. Extrapolation to the whole state forest (43.8 km2), the figures are respectively 172 and 48-56 breeding pairs. A similar phenomenon occured in 1971 and 1977 but to a lesser extend. These birds'habitat normally consists of semi-open countryside but on this occasion there was a marqued preference for the heart of the beech forest. Some pairs of Long-eared Owls nested also in neighbouring gardens. The main food source for these owls was Wood Mice instead of the usual Voles; that for the Kestrel was the Bank Vole. This unusual abundance in a forest was linked to a rodent population boom, itself the result of a heavy beech mast harvest in 1990, followed by a dry Spring in 1991. Concerning the Long-eared Owl, this exceptional abundance was seemingly also due to high over-wintering or post-wintering numbers, some birds remaining further to nest, as well in the agricultural areas of Brabant, as in the Forêt de Soignes itself.

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