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Despite being aware of the fact that splitting the year into homogeneous, rigidly distinct biological phases, valid for any species and geographical context, means forcing the biological reality, in order to characterize and compare the birds assemblages among sites and periods along the year, I performed a cluster analysis out of the Passerines 1982-2001 ringing data set (excluding Corvids and Hirundines), with the aim of clustering the thirty-six annual 10-day intervals on the basis of the degree of similarity in the composition and structure of birds assemblages sampled. The results comparison of the many approaches used suggest 9 periods: 1) Dec. 11-Feb. 10; 2) Feb. 11-Mar. 10; 3) Mar. 11-Apr. 10; 4) Apr. 11-May 20; 5) May 21-Jul. 20; 7) Jul. 21-Aug. 31; 9) Sep. 1-Sep. 30; 10) Oct. 1-Oct. 31; 11) Nov. 1-Dec. 10.
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