Aves, p�le ornithologique de Natagora

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Aves, 25/2 | 1988 | 116-130

  Contribution to the study of Common Gulls (Larus canus) wintering in Belgium.
Schmitz, L. & Degros, E.

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During the course of winters 1985-1986 and 1986-1987, gulls were counted and caught at a rubbish tip in Henri-Chapelle. The affluence of Common Gulls was very pronounced during these two harsh winters. Their numbers increased in January, culminating in February to drop in March. Much more than is the case with the Black-headed Gull and the Herring Gull, the winter movements of the Common Gull are distinctly connected with the rigours of the climate. The wing-length of the 845 Larus canus caught was measured; the variations of this parameter which indicates the sex of the bird, showed a tendency of an ebb and flow of the wintering birds in proportion to the cold spells and successive milder weather. 5 % of the 333 adults could be determined on the basis of wing-length as being heinei; the actual proportion, however, must be much higher, and during winters as harsh as above, shoult attain at least a quarter of the effectives.

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