Moult pattern of primaries and secondaries during first and second flight feather molt in Great Grey Owls Strix nebulosa

Roar Solheim

doi:10.34080/os.v21.22610

Abstract

Great Grey Owls start flight feather moult when in their second year. Moult was studied on outspread wings of 58 individuals in the collections at Naturhistoriska Riksmuseet in Stockholm. The owls always moulted the innermost secondaries in their first moult, and usually at least two primaries, most often P5 and P6. After this moult, birds had 11–17 juvenile feathers left in each wing, of a total of 21 flight feathers. In their second flight feather moult, birds shed primaries outwards and inwards from the primaries moulted during the first moult. A variable number of secondaries outwards from S10 and S11 were moulted. All birds retained at least one juvenile feather, always P1. The number of juvenile flight feathers after the second moult was 1–6. The collection held no individuals known to be in their third flight feather moult. Thus it was not possible to determine whether birds in this age group could be aged by the wing moult pattern. Great Grey Owls with no juvenile flight feathers should thus be classified as 4C+ in autumn, and 5C+ in spring.

Highlights

Very little is written on the moult of large feathers in owls. Mikkola (1983) does not cover this field, but in Cramp (1985) moult of flight feathers is described, mostly based on studies of captive birds
The birds moulted 4–10 flight feathers per wing. This means that a Great Grey Owl after its first flight feather moult (2CA and 3CS) has a mean of 14.3 juvenile flight feathers left in each wing.The moult pattern of a bird in this stage is recognized
The moult patterns of Great Grey Owls as revealed by the skin material at Naturhistoriska Riksmuseet (NRM), are in accordance with the description given in Cramp (1985), with moult of primaries starting with P5 or P6

Summary

Introduction

Very little is written on the moult of large feathers in owls. Mikkola (1983) does not cover this field, but in Cramp (1985) moult of flight feathers is described, mostly based on studies of captive birds. Year the moult continues, and the birds shed some of the older feathers In their third moult (as 4C) or even later, the last juvenile feathers are usually lost in the largest species. Based on work on Great Grey Owls Strix nebulosa in late autumn 2009 (Solheim 2009), I wanted to get a better insight into the moulting pattern of this great owl. This species moults a limited number of primaries and secondaries each year (Cramp 1985), thereby creating very distinct and visible moult patterns in the wings of older birds (see Solheim 2009, 2010). I was kindly allowed to visit the museum 12–15 January 2010, with access to the bird skin collections

Material and method

Discussion