The growth patterns of 36 flight feathers (12 primaries, 12 secondaries and 12 tail feathers) were studied in three Milvus migrans and three Buteo buteo. The length increases were registered every day. Ten mm/day was the maximum value obtained. The mean growth rate for feathers was 4.3 mm/day for the Common Buzzard and 4.4 mm/day for the Black Kite. The modal growth rate was 5 mm/day for the two species. The mean growth rate was associated directly with the final length of the feathers. The longest feathers showed the highest growth rates. Generally, growth rates were similar between species, with little differences in the mean growth, that seems independent of the total number of growing feathers and enviromental and trophic pressures.
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