Stanisław Kuźniak, Grzegorz Lorek, Sławomir Maćkowiak, Jakub Z. Kosicki Gawron Corvus frugilegus na Ziemi Leszczyńskiej The Rook Corvus frugilegus in the Leszno Province ABSTRACT: Distribution of the Rook breeding colonies was studied during the 80-ies and 90-ies and in 2002 in former Leszno Province (4154 km 2 ). In the studied area in the middle of the 80-ies there were around 6200 pairs in 86 colonies. In the 90-ies there were 54 colo- nies with 2881 pairs and in 2002 only 2649 in 58 colonies (Table 1, Fig. 1–3). So a steady de- cline of the breeding population was recorded. The decline between 80-ies and 90-ies was 53%, and by the year 2002 the breeding population decline further 8%. So in 2002 the Rook breeding population in the Leszno province was only the 43% of the one in 80-ies. All the re- corded colonies were located (except one) within human settlements. During the study in cities the number of colonies and nests was rather stable. In small cities the number of colo- nies was stable but the number of breeding pairs declined. In villages both the number of colonies and their size declined very distinctly. In the 80-ies 56% of the population studied bred in villages, in the year 2002 only 29% of the study population. Rooks build their nests mainly in parks and in different tree groups and tree alleys. The lowest number of colonies was located on isolated trees. The mean breeding density of Rook in Leszno province was about 1,5 p/km 2 in the 80-ies, 0,7 p/km 2 in the 90-ies, and 0,6 p/km 2 in the year 2002. Si- multaneously with the general decline in numbers the decrease in the mean size of the breeding colony was also recorded. In the 80-ies the mean colony size was 72 nests, in 90-ies – 53 nests, and in 2002 – 46. In every studied period small colonies dominated – up to 50 nests. In the 80-ies and 90-ies they represented 62% and 78% respectively and in 2002 – 81% of all colonies (Table 2). For many years the biggest colony has been located in the local park of Kościan. As early as in 1974 there were already 531 nests (Jakubiec 1980), in 1986 – 397 pairs, in 1996 – 568, and in 2002 – 569 pairs. In the year 2002 Rooks built their nests on Jerzak L., Kavanagh B.P., Tryjanowski P. (red.) Ptaki krukowate Polski [Corvids of Poland] Bogucki Wyd. Nauk., Poznań 2005 Stanisław Kuźniak, Grzegorz Lorek, Sławomir Maćkowiak, ul. Gen. Sikorskiego 28/10, 64-100 Leszno, e-mail: stakuz@poczta.onet.pl Jakub Z. Kosicki, Zakład Ekologii Behawioralnej, Uniwersytet im. A. Mickiewicza, ul. Umul- towska 89, 61-614 Poznań, e-mail: kubako@amu.edu.pl