\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[english]{babel}



\usepackage{float}








\begin{document}

\title{Moult Terminology: Envisioning an Evolutionary Approach}



\author[1]{Peter Pyle}%
\author[2]{Steve N. G. Howell}%
\author[3]{Danny I. Rogers}%
\author[4]{Chris Corben}%
\affil[1]{The Institute for Bird}%
\affil[2]{Point Blue Conservation Science}%
\affil[3]{Arthur Rylah Institute for Environmental Research}%
\affil[4]{The Institute for Bird Populations}%


\vspace{-1em}



  
  \date{May 22, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup








\sloppy


\textbf{Moult Terminology: Envisioning an Evolutionary Approach}

The study of avian moult has been inhibited not only by its complexity
but by convoluted and often conflicting terminologies that have combined
to cloud the subject. Over time, two nomenclatures have emerged with
differing bases of definition. The 'life-cycle' system is used widely in
European literature (e.g., Cramp 1988, Jenni \& Winkler 2020) and
defines moult terms based on timing relative to current-day life-history
events, primarily breeding. Conversely, the Humphrey-Parkes or 'H-P'
system (Humphrey \& Parkes 1959, as modified by Howell et al. 2003), is
used more widely in the New World and Australia (e.g., Higgins \& Davies
1996; Pyle 2008, 2022a; Howell 2010), and defines terms based on the
principle of how moults have evolved along avian lineages (Pyle 2022b).

Recently, Kiat (2022) proposed that moult terminology be simplified, and
advocated use of the life-cycle approach as a more understandable system
to those not familiar with moult terminology. We appreciate and endorse
Kiat's (2022) plea for a simpler moult terminology, and we empathize
with his frustration, but we disagree with his primary conclusion. We
argue that if one intends moult to be a subject for study, then a
standardized terminology based on the best scientific evidence is
preferable to a system that, while perhaps more widely understood among
ornithologists and the general public for passerines in boreal regions,
is often imprecise or ambiguous and is difficult to apply to the
majority of avian taxa on a global basis (Higgins \& Davies 1996, Howell
et al. 2004, Johnson and Wolfe 2018, Kiat 2022, Pyle 2022b).

The debate over the best moult and plumage terminology to use has
persisted since the H-P system was proposed by Humphrey and Parkes
(1959) over 60 years ago (e.g., Howell et al. 2003, 2004; Jenni and
Winkler 2004, 2020; Kiat 2022; Pyle 2022b; and references therein). At
this point, certain opinions on which system should be favoured are
calcified, and we do not wish to belabour the details yet again. In our
experience, however, newer students grasp the H-P system quickly,
whereas older ornithologists---including ourselves---who first learned
life-cycle moult terminology, often have initial difficulty envisioning
the H-P system's evolutionary approach. Our goal with this perspective
is to propose and illustrate how moults may have evolved in birds, with
the hope that it will assist future ornithologists to envision and
appreciate the H-P system.

Adhering to the evolutionary H-P approach, we propose considering the
prebasic moult, and perhaps the preformative moult, as ancestral to all
modern bird lineages, having evolved from reptiles (Howell \& Pyle 2015,
Pyle 2022b; see also Kiat et al. 2020, 2021; Figs. 1, S1). The complete
or near-complete prebasic moult occurs in all current-day avian taxa
and, rather than simply a replacement of feathers, appears to be part of
an endogenous restoration of body tissues (Voitkevich 1966, Murphy 1996,
Kuenzel 2003) that may be ancestral to all vertebrates (King 1972).
Considering the prebasic moult as homologous among modern birds is thus
a parsimonious hypothesis, providing a robust nomenclatural framework
that can be applied to all bird moults and plumages. The preformative
moult also appears to be present in most if not all modern bird
lineages, and may have evolved in reptiles as body size developed
quickly in the first year of life; if not, it evolved early in avian
evolution as it is found in most or all basal lineages (Figs. 1, S1).
Assuming homology among all modern bird taxa, the prebasic and
preformative moults can provide the framework for defining all
subsequently evolved moults within the H-P system (Figs. 1, S1).
Additional inserted moults, including prealternate and presupplemental
moults, can evolve (both appearing and disappearing) along bird lineages
such that, unlike prebasic and preformative moults, they should not be
considered homologous across all birds (Howell et al. 2003, Johnson and
Wolfe 2018, Pyle 2022b).

Once an evolutionary basis is appreciated, moult strategies become
substantially easier to compare across all species and latitudes. For
example, the four underlying strategies identified by Howell et al.
(2003), which are defined by the number of moults that occur within the
first and later moult cycles, can be provisionally placed in an
evolutionary context (Fig. 1; see Supporting information file and Fig.
S1 for details). Although it is quite possible that inserted moults may
have disappeared without trace along some bird lineages, envisioning how
these four strategies may have evolved for current taxa has the
potential to help inform a greater appreciation for the adaptive causes
of inserted moults (Figure S1).

We contend that the evolutionary (H-P) system is more applicable on a
global basis for studying avian moult than is the life-cycle system, and
we thus encourage those who use the life-cycle system to also attempt
visualizing an evolutionary approach to moult terminology, rather than
trying to simply synonymize H-P terms with life-cycle terms. We suggest
first determining the prebasic moult cycle, then whether or not inserted
moults occur in the first and/or later cycles, and using an evolutionary
approach to infer the correct designation of each inserted moult. Once
envisioned, learned, and appreciated, the evolutionary approach proposed
by Humphrey \& Parkes (1959), as modified by Howell et al. (2003), is
scientifically more precise, allows the recognition of all inserted
moults, and is easier to apply consistently, to all taxa and by all
parties interested in the study of moult in birds. We provide more
detail on taking an evolutionary approach in the Supporting information
file.

\textbf{Figure Legend}

\textbf{Figure 1.} A theoretical evolutionary approach to moult in birds
from reptiles, using the four moult strategies defined by Howell et al.
(2003; see also Howell 2010). The phylogenetic tree is based primarily
on that of del Hoyo \& Collar (2014, 2016) with some revisions to
reflect recent systematic advancements (see Supporting information file
for the use of this tree during times of phylogenetic flux). The four
strategies are Simple Basic (SBS; no preformative or prealternate
moults), Complex Basic (CBS; a preformative moult but no prealternate
moults), Simple Alternate (SAS; a single moult in the first cycle and
prealternate moults in later cycles), and Complex Alternate (CAS; a
preformative moult in the first cycle and prealternate moults in all
cycles). Here we propose that both prebasic and preformative moults, and
hence the Complex Basic Strategy (purple lineages in the figure), are
ancestral to all modern birds, although further study is needed on when
preformative moults evolved in primitive avian taxa or reptiles
ancestral to birds. Prealternate (and presupplemental) moults have
evolved many times along different lineages and should not be considered
homologous. See Supporting information file for an expanded version of
this phylogenetic tree (Fig. S1) along with detailed explanation and
discussion.

\textbf{Data Availability Statement}

There are no data associated with this manuscript.

\textbf{ETHICAL NOTE}

None.

\textbf{REFERENCES}

Cramp, S. (ed). 1988. The Birds of the Western Palearctic. Vol. 5. :
Press.

del Hoyo, J., \& Collar, N. 2014. Illustrated Checklist of the Birds of
the World, Volume 1. : Lynx Ediciones.

del Hoyo, J., \& Collar, N. 2016. Illustrated Checklist of the Birds of
the World, Volume 2. : Lynx Ediciones.

Higgins, P.J., \& Davies, S.J.J.F. (eds). 1996. Handbook of Australian,
, and Antarctic Birds. Vol. 2. : Press.

Howell, S. N.G. 2010. Peterson Reference Guide to Molt in North American
Birds. : Houghton Mifflin Harcourt.

Howell, S.N.G., \& Pyle, P. 2015. Use of `definitive' and other terms in
molt nomenclature: A response to Wolfe et al. (2014). Auk 132: 365-369.

Howell, S.N.G., Corben, C., Pyle, P., \& , D.I. 2003. The first basic
problem: a review of molt and plumage homologies. Condor 105: 635-653.

Howell, S.N.G., Corben, C., Pyle, P., \& , D.I. 2004. The first basic
problem revisited: reply to commentaries on Howell et al. (2003). Condor
106: 206--201.

Humphrey, P.S. \& Parkes, K.C. 1959. An approach to the study of molts
and plumages. Auk 76: 1-31.

Jenni, L., and Winkler, R. 2004. The problem of molt and plumage
homologies and the first plumage cycle. Condor 106:188-190.

Jenni, L. \& Winkler, R. 2020. Moult and Ageing of European Passerines,
2nd Ed. London: .

Johnson E. I., \& Wolfe J. D. 2018. Molt in Neotropical birds: Life
history and aging criteria. : CRC Press.

Kiat, Y. 2022. Moult terminology: Let's make it simpler! Ibis 2022:
e13164 https//doi.org/10.1111/ibi.13164

Kiat, Y., Balaban, A., Sapir, N., O'Connor, J.K., Wang, M., \& Xu, X.
2020. Sequential molt in a feathered dinosaur and implications for early
paravian ecology and locomotion. Curr. Biol. 30: 3633--3638.

Kiat, Y., Pyle, P., Balaban, A., \& O'Connor. J.K. 2021.
Reinterpretation of purported molting evidence in the Thermopolis
Archaeopteryx. Communications Biol. 4: 837.

King, J. L. 1972. Adaptive functions of vertebrate molting cycles. Am.
Zool. 12: 77-93.

Kuenzel, W. J. 2003. Neurobiology of molt in avian species. Poultry Sci.
82: 981-991

Murphy, M.E. 1996. Energetics and nutrition of molt. Pages 158-198 in
Avian Energetics and Nutritional Ecology (C. Carey, Ed.). : Chapman \&
Hall.

Pyle, P. 2008. Identification Guide to North American Birds. Part 2.
Station: Slate Creek Press.

Pyle, P. 2022a. Identification Guide to North American Birds, Part 1,
2nd Edition. Knolls: Slate Creek Press.

Pyle, P. 2022b. Defining moults in migratory birds: A sequence-based
approach. J. Avian Biol. 2022: e02958.
https://doi.org/10.1111/jav.02958.

Voitkevich, A. A. 1966. The feathers and plumage of birds (English
translation). : October House Inc.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Fig1-molt-tree-JAB/Fig1-molt-tree-JAB}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

