Pattern and chronology of prebasic moult in wood-warblers (Parulidae)

Abstract

This study compared the pattern and chronology of the prebasic moult in seven warbler species (Parulidae) at two locations in Ontario. Yellow Warblers {Dendroica petechia) were the earliest to start flight feather moult. Ovenbirds (Se/urus aurocapillus) underwent the most rapid flight feather moult, being only 22 days. Yellow-rumped Warblers (D, coronata) had the longest moult period (62 days) and were the last species to finish moult. These findings suggested that some warblers overlap the early and final stages of moult with the later stages of breeding and/or the onset of migration. Furthermore, a positive correlation between the duration of moult and timing of migration for all species, except Ovenbirds, suggested that earlier migrants moult more quickly and later migrants take a longer period to moult. Ovenbirds may be anomalous with regard to moult scheduling and migration because of their atypical ecological and behavioural attributes or their systematic position among parulids. A combination of external and internal factors may explain variations in the relationship between breeding, moult, and migration in warblers, allowing each species to fine-tune the onset of prebasic moult accordingly. I examined the relationship between raggedness scores and moult rates among five species of wood-warblers with similar moult patterns to determine if raggedness could be used as an index of moult rates. Positive correlations between raggedness and moult rates derived from pooled recaptures, least squares linear regressions, and individual species recapture methods suggested that average raggedness for the primary and secondary scores within a determined primary moult score range is a good index of the rate of moult in warblers. Therefore, mean raggedness scores may be a useful tool for (1) providing baseline moult rate assessments in populations with insufficient recaptures, allowing for comparisons to other populations with known moult rates; and (2) estimating the rate and duration of moult in some species. I compared the timing and patterns of the prebasic body moult between Hatch Year and After Hatch Year American Redstarts (Setophaga ruticilla), and Hatch Year and After Hatch Yellow Warblers. Both species displayed no difference in the number of moulting individuals in each designated body region. In addition, moult started in early July and lasted until mid-August for both age classes of American Redstarts. In contrast. Hatch Year Yellow Warblers started body moult in late June to early July, whereas adults began body moult in mid-July. Both American Redstarts and Yellow Warblers displayed differences in intensity and timing of moult among specific body regions between age classes. In addition, After Hatch Year individuals of both species underwent body moult concurrently with primary moult. Extrinsic and intrinsic factors may contribute to the variations in body moult scheduling observed in these two species.