Common Fiscal (Lanius collaris) Linnaeus, 1766: comparative biometrics, moult data and criteria for the determination of age and sex

Abstract

We present measurement and moult data for both subspecies groups of Common Fiscal (Lanius collaris) that occur in Namibia: for 235 Southern Fiscals (L. c. subcoronatus) ringed in Namibia and nine Northern Fiscals (L. c. capelli) in Zambia. We compare our observations of the moult process and our records of active brood patches with previous breeding records from Namibia (Brown et al. 2015) to gain a better understanding of the species’ annual cycle. In addition to the account of moult data in adults, we give those of first-year birds and describe in detail the plumage development through the discernible age groups: from fledgling to juvenile and immature, as well as second-year birds and adults. Furthermore, we discuss the possibility of a second generation of juvenile feathers as described in Palaearctic passerines, including the Laniinae, which has not yet been reported in the literature on African birds. Based on photographic evidence, we discuss the different plumages that we observed during more than 15 years of ringing. We add notes on interrupted moult, bi-focal moult, residual feathers of former plumage, recaptures and site fidelity, and precipitation and related numbers of shrikes. This monograph supplements published data and is intended to encourage further discussion and research relating to: subspecies measurements and description of juveniles of different subspecies, the different phases of feather growth of the juvenile plumage and their developmental relation to post-juvenile moult, the occurrence of residual feathers from former plumages throughout the different age groups, and the complexities concerning the overlap of moult and breeding (including double and multiple broods).