Multiple circannual moult strategies: feather tract moult patterns for common birds of the central Fynbos region, South Africa

Abstract

When and where birds lose their feathers during the annual moult cycle is a fascinating subject, but there is little reported on patterns and strategies of moult for most African bird species. While there have been great advances in our understanding of primary feather moult strategies, information on further plumage moult is generally lacking. This work reports on patterns of body, tail and head moult for 19 commonly captured species from ringing sessions mostly from the Blue Hill Nature Reserve in the Kouga Mountains, Western Cape province, South Africa, and surrounding mountain ranges. This is a temperate, aseasonal rainfall region, with ringing locations situated in the Fynbos biome. We used logistic generalised additive models to explore and visualise the annual patterns of head, tail and body moult in the context of primary feather moult for adult, non-migratory species. While we expected, and found, a degree of synchrony with primary and other feather moult, several interesting species-specific alternative strategies were also observed, with periods of extended or staggered moult across the annual cycle. For all species the moult period followed published breeding periods and, for most, peaked in the late austral summer period. However, there were many variations in tract moult between species with respect to initiation, duration and synchrony with other tract moult, as well as for sex, for two of the four sexually dimorphic species with sufficient data to explore this parameter. Additional moult based on presence/absence is commonly recorded by ringers, and submitted to the South African Bird Ringing Unit (SAFRING), but this data has seldom been analysed. We encourage ringers to do this for species they commonly encounter, as further interesting facets of life-history strategies await to be discovered.