Urban European Blackbird (Turdus merula L.) population was studied in 1997–2004 in two city parks of Szczecin (NW Poland), based on observations of colour-ringed birds. Biometric studies involving numerous bird species showed that the wings of individuals in their second year of life are shorter than those of birds older than two years; the causes of the differences are, however, unclear. The wing length of the individuals observed the year following the ringing was similar to that of the individuals that were not observed that year (probably non-survivors) –127.2 vs. 127.5 mm for young birds, 129.9 vs. 128.3 mm for old birds, respectively. Therefore, the hypothesis assuming increased mortality of shorter-winged individuals has to be rejected. In opposition to the expected differences between the wing to tail length ratios in the young and older birds (1st year – 1.43, 2nd year – 1.40, older – 1.39) one has to reject the hypothesis that the young individuals benefit from higher maneuverability of shorter wings. On the other hand, the greater wing length of those individuals captured in their second year of life and recaptured one year later (127.2 vs. 129.7 mm respectively) allows to accept the hypothesis of better nutrition as the cause of longer wings in the older blackbirds.
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