Timing and sequence of moult, and the trade-off with breeding, in the Speckled Warbler (Chthonicola sagittata)

Abstract

We examined the timing, sequence and rate of moult and its relationship to breeding in a small, insectivorous passerine, the Speckled Warbler (Chthonicola sagittata). Adult Speckled Warblers moulted remiges and rectrices during a discrete annual event in summer and autumn, with the onset of moult varying by up to 41 days between successive years. Speckled Warblers breed in simple pairs or in trios of a female and two males (alpha (α) and beta (β)). There was no difference in timing of the onset of primary moult for breeding males (α males in trios or simply paired males) and females in the population, although β males appeared to begin moult earlier than other adults. Speckled Warblers routinely overlapped moult with breeding, with the start of primary moult coinciding with the final breeding attempt for the season. Birds that bred late in the season began moulting earlier in their final nesting attempt compared with birds that completed breeding earlier in the season, suggesting a trade-off between these energy-demanding processes. The species displayed a typical descendent pattern of primary moult in which inner primaries were shed first and replaced in an outward direction. Rate of primary moult varied from 0.37 to 1.14 units per day (mean ± s.e: 0.64 ± 0.15), where 50 units equates to the complete replacement of all ten primaries. These data suggest a full primary moult takes between 44 and 135 days (mean = 78). Moult of secondaries began after several primaries had moulted. Primary moult overlapped extensively with moult of body and tail, with primaries usually moulting first. Juvenile Speckled Warblers, even those that hatched early, rarely began moult of flight-feathers during their first year of life. Instead they moulted feathers of the body and head, and delayed moult of flight-feathers until their second year.