From two to three individual feathers, a 0.3 cm segment was cut from the calamus end and placed in a 1.5 ml Eppendorf tube. Genomic DNA was extracted using of the GenEluteTM Mammalian Genomic DNA miniprep Kit (Sigma, Milano, Italy) according to the manufacter's instructions. Digestion was performed at 55 °C overnight using 200 μl of Lysis solution T (B6678) and 20 μl proteinase K (20 mg/ml).