Moult pattern of primaries and secondaries in Eagle Owls Bubo bubo

Abstract

Moult of primaries and secondaries of Scandinavian Eagle Owls Bubo bubo was studied from 42 museum specimens of which the birds'age was known. During their second year they moult the three innermost secondaries (S 13-15). The following summer the moult of secondaries progresses outwards. Primary P7 is moulted, and in many birds also P6 and P8. During their third moult in their fourth summer, Eagle Owls may moult the last secondaries, but still retain 2-3 (4) of the innermost primaries. Even after the fourth moult in their fifth summer, some Eagle Owls may still have some, or at least one, juvenile flight feather left. However, as some birds may lose all juvenile feathers at this stage, Eagle Owls should not be aged higher than 5C+ in autumn, and 6C+ in spring. Scandinavian Eagle Owls seem to moult their flight feathers at a slower pace than other large owls.