Despite its importance to birds, molting patterns have been neglected in comparison to other life-history events such as breeding, wintering, and migration strategies. This neglect has resulted in several historical molt and plumage terminologies that were based on proximal factors, were incongruent with each other, and obscured a clear evaluation of molting strategies. In 1959, Humphrey and Parkes ("H-P") proposed a system that named molts based on a tracing of their evolutionary history and development (Humphrey, P. S. and K. C. Parkes. 1959. An approach to the study of molts and plumages. Auk 76: 1-31.)
In 2005, Pyle traced homologous molts from Anserinae (which lack additional inserted molts) to Anatidae and concluded that the bright fall and winter plumage in male ducks of many species resulted from a complete prebasic molt and that it thus should be considered the basic rather than the alternate plumage. This was contrary to the traditional thinking, where the bright male plumages of ducks were considered alternate, as they are in other groups such as sandpipers and warblers (Pyle, P. 2005. Molts and plumages of ducks. Waterbirds 28: 208-219).
In a 2011 rebuttal to Pyle, Hawkins defended traditional terminology while continuing to promote ensuing plumage color as an important factor driving the evolution of molts in birds (Hawkins, G. L. 2011. Molts and plumages of ducks (Anatinae): an evaluation of Pyle (2005). Waterbirds 34: 481-494).
In the March 2013 issue of Waterbirds, Pyle responded to Hawkins by suggesting that the prebasic molts in geese, ducks, and other birds likely evolved from wholescale restorative events common to all vertebrates, whereas distinguishable and less-comprehensive endocrinological and metabolic processes may accompany later-evolved inserted molts. Pyle defended his 2005 interpretation by applying this ancestral definition of the prebasic molt through geese to ducks. Pyle also proposed an alternative interpretation for the initial evolution of two (rather than one) inserted molts in the definitive cycles of female and male ducks (Pyle, P. 2013. Molt homologies in ducks and other birds: a response to Hawkins (2011) and further thoughts on molt terminology in ducks. Waterbirds 36: 75-79).
There is still much to learn about molt in birds; e.g., we don’t know where the prebasic molt occurs in many birds. It also may be very difficult to trace the evolution of molts, since it is possible that inserted molts may have regressed as well as arisen evolutionarily. However, the assumption that the prebasic molt is an ancestral restorative process that evolved from reptiles to prehistoric birds to modern-day birds, and that subsequently inserted molts may show identifiable metabolic signatures, provides a foundation that paves the way for a better nomenclature and thus a better overall understanding of molt in birds.
Attachments: Pyle%202005.pdf Hawkins%202011.pdf Pyle%202013.pdf