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Résumé :
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In Vienna, Austria, a first extensive census of Jackdaws (Corvus monedula) revealed a total of 697 breeding pairs at 387 sites. A proportion of only 1.6 % of these sites was occupied by single breeding pairs. Population density exhibited 2.5 breeding pairs per km2. Except for the inner city centre and the areas situated south and west of it all city districts were populated by Jackdaws. Concentrations of breeding pairs (bp) were only found in the 21st (404 bp), the 22nd (91 bp) and the 2nd district of Vienna (73 bp). About 92 % of all breeding pairs selected breeding places at buildings whereby the inside of chimneys accounted for nearly 60 % of all breeding places. The latter were mainly apparent in the 21st district where the birds form extensive colonies when breeding in neighbouring chimneys. Jackdaws nesting in holes and niches of the outer surface of the building mainly occur in a few high density colonies in the 22nd district as well as in many small stocks spread over the 2nd district. Only 8.2 % of all breeding pairs nest in natural tree hollows, primarily in old plane trees of parks and avenues. Since nest sites of Jackdaws in Vienna are endangered due to demolition, renovation of buildings, removal or closing of chimneys and pruning of trees, a conservation concept to preserve used breeding places and to provide new alternative nesting sites is proposed.
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