  Molt is an essential life-history event in birds and many mammals, as
maintenance of feathers and fur is critical for survival. Despite this molt
remains an understudied life-history event. Non-standard statistical techniques
are required to estimate the phenology of molt from observations of plumage or
pelage state, and existing molt phenology models have strict sampling
requirements which can be difficult to meet under real-world conditions. We
present an extended modelling framework that can accommodate features of
real-world molt datasets, such re-encounters of individuals, misclassified molt
states, and/or molt state-dependent sampling bias.
  We demonstrate that such features can lead to biased inferences when using
existing molt phenology models, and show that our model extensions can improve
inferences about molt phenology under a wide range of sampling conditions. We
hope that our novel modelling framework removes barriers for modelling molt
phenology data from realworld datasets and thereby further facilitates the
uptake of appropriate statistical methods for such data. Although we focus on
molt, the modelling framework is applicable to other phenological processes
which can be recorded using either ordered categories or approximately linear
progress scores.
