A demonstration of the value of recapture data for informing moult phenology models for avian species with imperfect moult data

Abstract

The Underhill–Zucchini model has revolutionised the study of moult in the context of birds’ annual cycles, but, as for all statistical models, inferences are vulnerable to violations of model assumptions. In particular, the standard Underhill–Zucchini models for moult phenology are vulnerable to imperfect moult data arising, for example, from non-random sampling and/or the misclassification of non-moulting birds. Similarly, inference is challenging for species with dispersed moult periods (population-level moult extending beyond an annual cycle). Using ringing data from Cape Weavers Ploceus capensis and SAFRING data for Cape Sugarbirds Promerops cafer, we demonstrate how recent extensions to the Underhill–Zucchini framework can help the robust estimation of moult parameters in such situations, in particular when within-season recapture data is available.