SCHREVEN K & VAN DER HORST Y (2016) A sparrowhawk Accipiter misus nestling without cartenoid pigmentation.. LIMOSA 89 (1): 23-26.

On 21 June 2015 an abnormally coloured female Sparrowhawk nestling was ringed in a brood of two males and three females in a woodlot near Nijmegen, The Netherlands. It lacked yellow pigmentation in leg skin, cere and iris, which appeared white, blue and blueish grey respectively. Feathers, nails and bill were coloured as normal. The bird's four siblings were coloured normally. All nestlings were in good body condition and probably the whole brood fledged. It is likely that the observed aberration in the female nestling is a genetic disorder. According to literature, the yellow pigmentation in raptor leg skin is caused by a carotenoid, and the mutation may relate to an increased expression of the beta-carotene oxygenase 2 (BCO2) gene, which causes the leg skin in chickens to be white. However, in pet birds multiple mutations (autosomal, both dominant and recessive) are known to cause loss of carotenoid pigmentation. Whether the observed abnormality in the female nestling resulted from a spontaneous dominant mutation or from inherited recessive alleles is unknown as the parental phenotypes were not determined. The female nestling with this mutation was the first among 5500 Sparrowhawk nestlings ringed near Nijmegen, as well as among 18 311 Sparrowhawk nestlings ringed by colleagues at other locations in the Netherlands, Germany and Scotland. This corresponds to 0.0042% of the individuals. Although the female nestling appeared healthy, we cannot exclude that the lack of yellow pigmentation had negative effects. Potential consequences of this mutation may occur during pair formation, as bright carotenoid-based colouration is generally a sexually attractive trait. Especially in males, this could constitute a selection pressure against this mutation.

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