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Winter quantitative studies on the Rook Corvus frugilegus, Hooded Crow Corvus cornix and Jackdaw Corvus monedula were conducted independently by two observers in the season 1999/2000 in fragments of urban green areas in Bydgoszcz and Toruń. Each observer visited all plots six times at different dates and did two subsequent counts the same day, noted as the early and the late one, respectively. The...
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