Wild common crossbills produce redder body feathers when their wings are clipped.

Clipped birds lost about 1.7% of their initial body mass (difference to zero: t = − 3.03, df = 13, p = 0.010), whereas controls showed a statistical trend to increase body mass in a similar proportion ( t = 1.96, df = 19, p = 0.065; Fig. 1 ).

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However, among recaptured birds, individuals with experimentally impaired flying capacity showed body mass loss, whereas controls showed a trend to increase their weight.

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