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Searching for consensus in molt terminology 11 years after Howell et al.'s “first basic problem”


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Howell et al. (2003) published an innovative augmentation to terminology proposed by Humphrey and Parkes (1959) that classified bird molt on the basis of perceived evolutionary relationships. Despite apparent universal applicability, Howell et al.'s (2003) proposed terminological changes were met with criticism that cited a failure to verify the evolutionary relationships of molt and an inability to recognize homologous molts even within closely related taxa. Eleven years after Howell et al. (2003), we revisit arguments against a terminological system of molt based on evolutionary relationships, suggest an analytical framework to satisfactorily respond to critics, clarify terminology, and consider how to study molt variation within an evolutionary framework.
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Volume 131, 2014, pp. 371–377
DOI: 10.1642/AUK-13-087.1
Searching for consensus in molt terminology 11 years after Howell et al.’s
‘‘first basic problem’’
Jared D. Wolfe,
* Erik I. Johnson,
and Ryan S. Terrill
U.S.D.A. Forest Service, Pacific Southwest Research Station, Redwood Sciences Laboratory, Arcata, California, USA
Klamath Bird Observatory, Ashland, Oregon, USA
School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, USA
National Audubon Society, Baton Rouge, Louisiana, USA
Museum of Natural Science, Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, USA
* Corresponding author:
Received April 7, 2014; Accepted April 10, 2014; Published June 18, 2014
Howell et al. (2003) published an innovative augmentation to terminology proposed by Humphrey and Parkes (1959)
that classified bird molt on the basis of perceived evolutionary relationships. Despite apparent universal applicability,
Howell et al.’s (2003) proposed terminological changes were met with criticism that cited a failure to verify the
evolutionary relationships of molt and an inability to recognize homologous molts even within closely related taxa.
Eleven years after Howell et al. (2003), we revisit arguments against a terminological system of molt based on
evolutionary relationships, suggest an analytical framework to satisfactorily respond to critics, clarify terminology, and
consider how to study molt variation within an evolutionary framework.
Keywords: first basic problem, Howell et al. (2003), molt cycle, molt strategies, molt terminology, phylogenetic
Buscando consenso en la terminolog´
ıa de la muda 11 a ˜
nos despu ´
es de Howell et al. ‘‘ la problema del
primero basico’’
Howell et al. (2003) public ´
o una argumentaci ´
on innovadora para la terminolog´
ıa propuesta por Humphrey y Parkes
(1959) que clasificaba la muda de las aves basada en las relaciones evolutivas percibidas. A pesar de la aplicabilidad
aparentemente universal, los cambios terminol ´
ogicos propuestos por Howell et al. (2003) fueron considerados con
criticismo aduciendo a una dificultad para verificar las relaciones evolutivas de la muda y una falta de habilidad para
reconocer las mudas hom´
ologas incluso adentro de taxones cercanamente relacionados. Once a ˜
nos luego de Howell
et al. (2003) revisamos los argumentos en contra de un sistema terminol ´
ogico de la muda basado en las relaciones
evolutivas, sugerimos un marco anal´
ıtico para responder satisfactoriamente a las cr´
ıticas, clarificamos la terminolog´
ıa y
consideramos como estudiar la variaci ´
on de la muda adentro de un marco evolutivo.
Palabras clave: ana
´lisis filogen´
etico, ciclo de la muda, estrategia de la muda, Howell, la problema del primero
basico, terminolog´
ıa de la muda
Terminology for molt, the scheduled replacement of
feathers, is unnecessarily redundant, as exemplified by
the multitude of terms for the same molt (Figure 1). The
abundance of jargon stems from classifying molt in
relation to environmental or life-cycle seasonality (e.g.,
breeding; Wolfe and Pyle 2012). Unfortunately, categoriz-
ing molt in relation to breeding or seasonality does not
provide a universal system of molt terminology because
not all birds breed every year or reside in seasonal
environments—a fact championed by ornithologists for
more than half a century (Humphrey and Parkes 1959,
1963, Rohwer et al. 1992, Howell et al. 2003, 2004). For
example, Humphrey and Parkes (1959:14) noted that
naming molts on the basis of ‘‘environmental and
endocrinal phenomena’’ is problematic because such
phenomena ‘‘may be related in different ways in different
groups of birds, and . . . these relationships can only be
obscured by making the nomenclature of plumages and
molts contingent on states of any other cycle or
developmental processes.’’
The problems cited by Humphrey and Parkes (1959) are
more than theoretical. For example, Jackson (1915) first
suggested that the summer body molt in most male ducks
should be aligned with the later complete wing molt and,
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because it produced a cryptic plumage, Jackson considered
this a ‘‘winter’’ plumage followed by a brightly colored
‘‘summer’’ plumage even though it occurs primarily in the
winter (Jackson 1915, Pyle 2005). Since Jackson (1915),
variations in the terminology for duck plumage and molt
have proliferated in the literature, resulting in a diverse,
confusing, and sometimes counterintuitive list of molt
nomenclature based on season and breeding status
(Schiøler 1921, Witherby et al. 1939, Dement’ev and
Gladkov 1952, Oberholser 1974, Cramp and Simmons
1977, Marchant and Higgins 1990). The misleadingly
descriptive and unstructured nature of such terminology
has undoubtedly suppressed or obscured comparative
studies in molt and plumage variation across taxa.
Humphrey and Parkes (1959), recognizing that classifica-
tion of molt on the basis of seasonality and life-cycle events
unnecessarily differentiates identical molts and ignores the
evolutionary history of molt diversification, proposed a
unifying system of molt terminology, later augmented by
Howell et al. (2003), in which molt terminologies were
modified to reflect perceived homologies (Table 1).
Importantly, the definition of ‘‘homology’’ used here and
by Humphrey and Parkes (1959) refers not to similarity of
structure or function, but to historical continuity through
inheritance with modification (Wagner 2007). Note that
we prefer the term ‘‘paralogy’’ to describe repeated molts
within a species because it more accurately reflects their
assumed evolutionary relationship, despite the previous
use of ‘‘homologous’’ by Howell et al. (2003) in such
circumstances, which is instead more appropriate for
cross-species comparisons.
The defining difference between Humphrey and Parkes
(1959) and Howell et al. (2003) lies in the naming of molt
sequences within a bird’s first year of life. Humphrey and
Parkes (1959) concluded that the prejuvenal molt is unique
because it does not have an apparent paralogy later in life.
Humphrey and Parkes (1959) also identified the first
prebasic molt (i.e. the molt immediately following the
prejuvenal molt) as paralogous, with subsequent prebasic
molts occurring approximately annually. Because not all
species of birds replace all or parts of their juvenal
plumage soon after leaving the nest (e.g., many Accipi-
tridae and waterbirds; Howell 2010) and because first
prebasic molts can range from being limited to complete
across species (Pyle 1997), Howell et al. (2003) modified
the terminology of Humphrey and Parkes (1959) by
considering the prejuvenal molt synonymous with the first
prebasic molt and reclassified the first prebasic molt as a
preformative molt that occurs only early in life and lacks
paralogous counterparts. As a result, Howell et al.’s (2003)
system (hereafter ‘‘H-P-H’’) considers the prebasic molt to
be a recurring (often annual) complete or nearly complete
paralogous molt, shared by all bird species, that arose deep
in evolutionary time; periods between prebasic molts are
called ‘‘molt cycles.’’ Howell et al.’s (2003) simple changes
succinctly aligned molts and plumages across a diversity of
taxa, thereby dramatically improving upon the termino-
logical system originally proposed by Humphrey and
Parkes (1959; see Howell et al. 2003:figure 1). Howell et
al. (2003) further suggested that selective pressures led to
the subsequent evolution of other molts inserted between
prebasic molts, like the preformative molt, and also
prealternate and presupplemental molts, defined by the
cycle in which they occur (Table 1). Recognizing the
number or type of inserted molt(s) within each cycle places
every bird into 1 of 4 ‘‘molt strategies’’ (Howell et al. 2003,
Pyle 2008, Howell 2010).
Substantiating H-P-H assumptions is an important step
toward more rigorously examining the diversification of
feathers and their maintenance through molt that has
allowed birds to colonize the Earth’s surface. Additionally,
understanding the nature of inserted molts would provide
FIGURE 1. Diagram showing the annual plumages of Indigo Bunting (Passerina cyanea), following Howell et al.’s (2003) terminology.
In addition to plumages, we included examples of redundant molt terminology associated with each plumage.
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The Auk: Ornithological Advances 131:371–377, Q2014 American Ornithologists’ Union
372 Molt terminology 11 years after Howell et al. (2003) J. D. Wolfe, E. I. Johnson, and R. S. Terrill
insights into why certain avian lineages were more prone
to acquiring extra molts, which may have facilitated life-
history evolution. For example, there appear to be
correlations between migratory behavior and the presence
and extent of inserted molts. These extra molts may have
arisen to mitigate structural damage associated with a
migratory lifestyle and subsequently commandeered to
reflect honest signals associated with winter-ground
quality through changes in plumage coloration (Svensson
and Hedenstr¨
om 1999, Pyle and Kayhart 2010, Wolfe and
Pyle 2011).
Like other physiological processes and behaviors, molts
have presumably resulted from an evolutionary history in
which simple adaptations preceded increasingly complex
ones. For example, birds molt their feathers at least once a
year, so parsimony suggests that an annual molt is a shared
characteristic that preceded later inserted molts (which are
not shared across taxa) and likely descended from their
most recent common ancestor, instead of having evolved
multiple times. Although highly variable in timing, this
presumably ancestral annual molt is not known to have
been lost in any extant birds (although geese may rarely
skip an annual molt; see Summers 1983, Summers and
Martin 1985), whereas the ability to fly has been lost
potentially hundreds of times (Steadman 1989). Given that
variation in molt insertions and in the timing of the annual
molt probably aided in the global radiation of birds, we
believe that a universal terminology encompassing the
diversity of molt will promote collaborative study and a
deeper understanding of avian evolution.
Here, to move us toward a unified molt terminology, we
provide a review of hindrances associated with H-P-H and
suggest an analytical framework to address such problems.
We also assess ambiguous terminology associated with H-
P-H and offer clarifications. Hereafter, to be as consistent
as possible, we follow Howell et al.s (2003) convention for
naming molts and plumages (see Table 1).
Problems with H-P-H and Classifying Molt by
Evolutionary History
Despite H-P-H’s potential to improve our understanding
of molt and despite its universal applicability, critics noted
the system’s many evolutionary assumptions, including
presumed and untested homologies across, and paralogous
annual molts within, species (Willoughby 2004, Jenni and
Winkler 2004). Other critiques of H-P-H suggested that
Howell et al. (2003) lacked appreciation for the plasticity of
molt, which can obscure homologies (Willoughby 2004,
Jenni and Winkler 2004). For example, diversity in the
number of molts, extent of each molt, and color of the
subsequent plumage can be tremendously variable among
closely related taxa such as cardueline finches, making the
identification of molt homologies difficult, if not impos-
sible (Willoughby 2004; but see Howell 2010). Additional
TABLE 1. Important molt and plumage definitions following Pyle (2008) and Howell (2010).
Terminology Description
Prebasic molt Prebasic molts occur approximately annually in most birds, are complete to nearly complete, and
delineate molt cycles. The first prebasic or prejuvenal molt results in the juvenal plumage. The
prejuvenal molt usually occurs soon after hatching and often replaces natal down. Juvenal plumage
is the first pennaceous coat of feathers. The prejuvenal molt is ubiquitous (occurring in all birds) and
is complete in extent (replacing all feathers). Howell et al. (2003) considered the prejuvenal molt
comparable with later prebasic molts and, therefore, synonymous with the first prebasic molt.
Preformative molt Results in the formative plumage. Synonymous with the first prebasic molt of Humphrey and Parkes
(1959). The presence and extent of the preformative molt are extremely variable across birds. The
preformative molt is unique because it occurs only within the first molt cycle and lacks counterparts
in subsequent molt cycles. Sometimes 2 preformative molts occur within the first molt cycle, in
which case a second preformative molt is referred to as the ‘‘auxiliary preformative molt.’’
Prealternate molt Results in the alternate plumage. The presence and extent of the pralternate molt are extremely
variable across birds. When it occurs, it is often the third molt in the first cycle (in addition to the
preformative molt) and the second molt found in each subsequent molt cycle (in addition to the
prebasic molt).
Presupplemental molt Results in the supplemental plumage, which can be the fourth molt in the first molt cycle (in addition
to the prejuvenal, preformative, and prealternate molts) and the third molt in subsequent molt cycles
(in addition to the prebasic and prealternate molts). If a species has additional presupplemental
molts, they are referred to as ‘‘presupplemental a,’’ ‘‘presupplemental b,’’ etc.
Molt cycle Period between prebasic molts. For example, birds enter the first molt cycle upon beginning their
prejuvenal molt; at the start of the second prebasic molt, they enter the second molt cycle.
Definitive Here, we suggest that ‘‘definitive’’ be used only to describe molts and plumages derived from
definitive molt cycles (second or later molt cycle for the majority of species). Definitive molt cycles
are defined as having molts with counterparts in subsequent cycles. Thus, first, most cycles that
exhibit preformative molts are not considered definitive, because the preformative molt occurs only
within the first cycle.
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The Auk: Ornithological Advances 131:371–377, Q2014 American Ornithologists’ Union
J. D. Wolfe, E. I. Johnson, and R. S. Terrill Molt terminology 11 years after Howell et al. (2003) 373
problems included difficulties in verifying Howell et al.’s
(2003) assumption of paralogy between prejuvenal and
later prebasic molts (Willoughby 2004, Jenni and Winkler
2004); even Howell et al. (2003:639) suggested that
prejuvenal and prebasic molts ‘‘may be analogous based
on a widely shared function’’ rather than resulting from a
shared evolutionary history and underlying physiological
process. An additional problem associated with H-P-H is
variation in the definition of ‘‘ molt strategy,’’ reflecting an
inability to differentiate inserted molts. Howell et al. (2003)
first defined different molt strategies by determining which
inserted molt occurs within a particular cycle (e.g.,
prealternate or preformative molt within the first cycle;
see Table 1). Pyle (2008) modified the definition of molt
strategies by identifying the number of insertions (e.g., 1 or
2 insertions within the first cycle), thereby recognizing an
inherent difficulty in distinguishing between first-cycle
prealternate and preformative molts in some species (e.g.,
Ancient Murrelet [Synthliboramphus antiquus]; Pyle
2009). Most recently, Howell (2010) seemingly hybridized
the 2 approaches by defining molt strategy on the basis of
number of insertions, which usually correspond to a
particular inserted molt, within a given cycle.
In response to critics, Howell et al. (2004) reiterated that
feather color should not be used to identify homologous
molts and that molt homology should be considered
‘‘comparable,’’ awaiting verification of evolutionary origins
when ‘‘a genetic basis will eventually be discovered that
can reveal homologies of molts’’ (Howell et al. 2004:207).
Although H-P-H may be correct in assuming that an
annual molt is highly conserved, note that timing of
development is one of the most variable elements of
evolution and that the vast majority of morphological
evolution occurs through changes in developmental timing
(West-Eberhard 2003). We propose that the evolution of
molt should be studied under the framework of heteroch-
rony, or changes in timing of developmental events.
Developmental events and associated regulatory genes
are evolutionarily malleable and easily duplicated, and
molt is a physiologically complicated process. Repeated
annual molts in birds are likely paralogous, and inserted
molts may be the result of duplication and modification of
an ancestral molt. On the basis of these realizations, we
believe that 2 questions must be addressed to verify H-P-H
assumptions and move toward a universally accepted
system of molt terminology: (1) What was the ancestral
molt? (2) How many times and why have inserted molts
Testing H-P-H Assumptions
One major obstacle in testing H-P-H assumptions is the
determination of whether the prejuvenal and later prebasic
molts are paralogous within, and homologous across, taxa.
Within species, the relationship between prejuvenal and
prebasic molts may represent a synapomorphic character
or, conversely, 2 independently derived traits with respect
to other molts. Distinguishing between these possibilities is
difficult because every known bird species has a molt
resembling the prejuvenal and prebasic molt, which limits
our ability to analyze variation within a phylogenetic
framework. If the prejuvenal and prebasic molts evolved
independently deep in evolutionary time, then regulation
of prejuvenal and prebasic molts may operate indepen-
dently and might be assessed through transcriptomic
analysis. Such an analysis could sample a diversity of
species and molts to assess how dissimilar molts are
activated within and across species. Results of a tran-
scriptomic analysis experiment would cluster molts by
their expression profile, allowing analysts to determine
expression and genetic similarities of molts within an
individual. Despite apparent potential for transcriptomic
analysis, we realize that molt is likely determined by many
genes, gene duplication, or manipulation in the timing of
events (Carroll 2008), thereby complicating molecular
analysis focused on determining the evolutionary relation-
ship of paralogous molts within a species.
Despite inherent difficulties in examining evolutionary
relationships of paralogous molts within species, variation
in patterns of the prebasic molt may shed some light on
this issue. All birds molt their feathers simultaneously
during the prejuvenal molt, and many groups of birds molt
remiges simultaneously as adults (e.g., Gaviidae, Rallidae,
Anatidae, Alcidae, and Gruidae; Pyle 2008). This retention
of a juvenile trait into adulthood may be viewed as an
example of neoteny. The fact that simultaneous molt, when
exhibited in adults, is expressed during prebasic molts and
never during the preformative or prealternate molts
provides evidence for ancestral relationship and physio-
logical connection between the prejuvenal and prebasic
molts (Pyle 2008). Because parsimony and similarities in
feather replacement strongly suggest a shared evolutionary
origin of annual molts (prebasic and prejuvenal) within
species, the number and extent of inserted molts
(preformative, prealternate, and presupplemetal molts;
see Table 1) between prebasic molts can be examined as
characters throughout a phylogeny to estimate relation-
ships between similar molts in different species, in much
the same way that behavior is examined by ethologists
(Greene and Burghardt 1978; Figure 2). Testing this
assumption would determine whether multiple insertions
within molt cycles (e.g., prealternate and preformative
molts) in gulls (Laridae) and warblers (Parulidae) are the
result of 1 or multiple evolutionary events. Realistically,
finding single origins for inserted molts across all bird taxa
is not likely and does not render the fundamental concept
of H-P-H nomenclature invalid; it would only necessitate
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The Auk: Ornithological Advances 131:371–377, Q2014 American Ornithologists’ Union
374 Molt terminology 11 years after Howell et al. (2003) J. D. Wolfe, E. I. Johnson, and R. S. Terrill
new definitions of inserted preformative, prealternate, and
presupplemental molts reflecting their homoplasy.
Clarification of Terms
In addition to testing H-P-H assumptions, ambiguous molt
terminology associated with H-P-H must be clarified. In
particular, the term ‘‘definitive’’ is used in 4 different
contexts: (1) plumage maturation (definitive plumage), (2)
molts that produce a fully maturated plumage (definitive
molt), (3) molts that have paralogous counterparts in
subsequent cycles (definitive molt), and (4) cycles that
include only molts with paralogous counterparts in
subsequent cycles (definitive molt cycle) (Humphrey and
Parkes 1959, Rimmer 1988, Heise and Rimmer 2000,
Howell et al. 2003, Pyle 2008). Originally, Humphrey and
Parkes (1959) suggested the term ‘‘definitive’’ to describe
maturated plumages; unfortunately, using ‘‘definitive’’ in
its original context is confusing, as exemplified by White-
crowned Manakins (Dixiphia pipra). In the first cycle,
these manakins undergo a partial preformative molt,
FIGURE 2. Schematic illustrating our proposed analysis whereby molt insertions are associated with individual species, across a
phylogeny, to ascertain whether insertions denote synapomorphies across distantly related taxa. Our schematic is based on the
phylogeny proposed by Sibley and Ahlquist (1990).
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The Auk: Ornithological Advances 131:371–377, Q2014 American Ornithologists’ Union
J. D. Wolfe, E. I. Johnson, and R. S. Terrill Molt terminology 11 years after Howell et al. (2003) 375
resulting in a green bird with some retained juvenal
feathers for the remainder of the first cycle. The second
prebasic molt is complete in extent, resulting in green
males and females without retained juvenal plumage. After
the third prebasic molt, females remain green (and are
identical to second basic females), but males transition to a
striking black and white plumage that is either fully
maturated or becomes fully maturated after the fourth
prebasic molt (Ryder and Dur˜
aes 2005). Therefore, despite
being the same age, female White-crowned Manakins
enter a ‘‘definitive plumage’’ (sensu Humphrey and Parkes
1959) 1 or 2 yr before males, even though a ‘‘ definitive
molt’’ or ‘‘definitive cycle’’ commences with the second
prebasic molt in both sexes. Some other species, such as
Wrentit (Chamaea fasciata), undergo a complete prefor-
mative molt that results in a fully maturated plumage
aspect, similar to second and later basic plumages (Pyle
1997). These 2 examples demonstrate that a definitive
plumage could result from a definitive preformative,
second prebasic, third prebasic, or fourth prebasic molt;
thus, the term ‘‘definitive’’ as currently used is context
dependent and confuses a discussion of evolutionary
relationships across and even within species.
We believe that using ‘‘definitive’’ to describe plumage
maturation violates the spirit of H-P-H, in which 1 molt
results in 1 plumage and is not used to classify plumage
aspect (Howell et al. 2003). Presumably on the basis of this
realization, Pyle (2008:13) used molts with paralogous
counterparts in subsequent cycles to define definitive
molts as attaining ‘‘stasis in terms of extent and timing,
irrespective of plumage aspect.’’ It may seem natural to
define definitive molts as having paralogous counterparts
in subsequent cycles (sensu Pyle 2008); however, this
definition presents inconsistencies where the prejuvenal
molt, presumed to be paralogous with later prebasic molts,
might be considered definitive but is followed by a
preformative molt that lacks counterparts in subsequent
cycles. We suggest that molt and plumage terminology
should be consistently applied across taxa to better reflect
presumed evolutionary history and, thus, recommend that
‘‘definitive’’ be used only in the context of describing molt
cycles and the molts that occur within them, irrespective of
plumage aspect. In this context, the second molt cycle
would represent the definitive molt cycle in most birds
and, therefore, individual molts occurring within the
second and later cycles should be considered definitive.
In conclusion, H-P-H is a unique system of nomencla-
ture because, like systematics and taxonomy, it strives to
base molt terminology on the evolutionary history of the
subject. However, no major attempt has been made to
validate the evolutionary framework in which H-P-H
classifies molt. To move toward molt nomenclature
consensus, the evolutionary assumptions of H-P-H must
be tested and the terminology solidified. Through phylo-
genetic analyses and a stronger understanding of under-
lying physiological and genetic controls of assumed
prebasic molts, researchers will begin to subject the H-P-
H system to continual refinement, thereby providing novel
insights into avian evolution and natural history.
Thanks to P. Pyle, G. Seeholzer, and two anonymous reviewers
who greatly improved the quality of the manuscript, and
thanks to S. Taylor’s graduate seminar class at Louisiana State
University for vetting the manuscript. This article was
approved for publication by the Director of the Louisiana
Agricultural Experimental Station as manuscript no. 2014-
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J. D. Wolfe, E. I. Johnson, and R. S. Terrill Molt terminology 11 years after Howell et al. (2003) 377
... We recorded the stage of molt in remiges (primary and secondary wing feathers) and rectrices (tail feathers), color and wear of the plumage following the terminology and criteria proposed to categorize age, cycles, and molting strategies in Neotropical birds (Johnson et al. 2011;Wolfe et al. 2014). To establish the molting intensity of the individuals during the sampling time, we scored flight feathers (primaries, secondaries, and rectrices) from 0 to 5 for each bird, taking as 0 the oldest feathers and 5 the newest feathers (Pinilla 2000;Marini and Durães 2001;Batista-Silveira and Marini 2012). ...
... We collected 39 individuals in active molt, 21 females (10 juveniles, 3 reproductive adults, and 8 non-reproductive females) and 18 males (8 juveniles, 3 reproductive adults, and 7 non-reproductive adults). Following molting characteristics and terminology (Johnson et al. 2011;Wolfe et al. 2014), we assigned the collected birds to 3 plumage-age classes: juvenile, formative, and definitive plumage (Supplementary Material Figs. S2-S6). ...
... Most juvenile individuals showed evident wear on their plumage, probably since the first generation of flight feathers (resulting from the first pre-basic molt), acquired months after the bird leaves the nest (Ryder and Wolfe 2009), wears out faster than later generations (Ralph et al., 1996). This juvenile plumage is replaced by the preformative molt that is usually partial or incomplete (Pyle et al. 2016;Gómez et al. 2012;Botero-Delgadillo et al. 2013;Wolfe et al. 2014) and is largely common of tropical passerines (Ryder and Wolfe 2009;Wolfe et al. 2009;Radley et al. 2011;Batista-Silveira and Marini 2012;Gómez et al. 2012;Botero-Delgadillo et al. 2013) as in temperate zones (Pyle 1997;Pyle et al. 2016). The pre-formative plumage (acquired as a result of the pre-formative molt) is replaced by the complete pre-basic molt, which is characterized by the replacement of all feathers, including coverts (Ralph et al., 1996;Ryder and Wolfe 2009;Gómez et al. 2012;Botero-Delgadillo et al. 2013;Wolfe et al. 2014). ...
The Carib Grackle (Quiscalus lugubris) has recently extended its distribution to montane habitats in the Colombian Andes, including urban areas. Little is known about its reproductive biology in both natural and urban environments. We analyzed the relationship between morphological and morphometric external characters with sex, reproductive condition, and the annual reproductive activity of two groups of individuals that inhabit the city of Bucaramanga, Colombia. We aimed to know if there is a clear association between external features (including plumage/molting) and sex, maturity, and reproductive stage. We recorded the external morphology of these individuals (molt, iris color, and brood patch presence) as well as standard morphometric traits and classified these birds in reproductive stages according to morphology and histological analyses of their reproductive tracts. We found a clear sexual dimorphism between adults in morphometric features and plumage color. However, neither morphometric features nor iris and plumage color/molt pattern clearly indicates sexual maturity; some immatures can be mistakenly taken as adults due to the morphological characteristics obtained after they complete their pre-basic molt. Females reach maturity at different body masses and could reproduce asynchronically; therefore, the presence and type of brood patch is the only useful feature for the identification of female reproductive stages. Quiscalus lugubris has an extended breeding season throughout the year and a seasonal molting activity; at the end of the second rainy season (November) and during the driest time of the year (December–January), adults exhibited reproductive tracts in regression and were found in active molt.
... Males have a definitive plumage with a bright white crown and fully black body, wings, and tail. This male plumage is "definitive" in the sense that it has reached a stasis; all future molts will result in a similar plumage (Howell and Pyle 2015; but see Wolfe et al. 2014). Females in this population have a different definitive plumage-olive green across the wings, body, and tail, with some gray in the face-that is achieved after the first year. ...
... The technical name of the plumage that arises from the first preformative molt is "first cycle formative" (previously known as "first basic"; Wolfe et al. 2014). This plumage appears identical across male and female P. pipra pipra. ...
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Synopsis Birds with delayed plumage maturation exhibit a drab predefinitive plumage, often despite gonad maturation, before developing the definitive plumage associated with increased reproductive success. Manakins are a diverse clade of neotropical lekking birds with extreme sexual dichromatism, radical sexual displays, and a unique diversity in the predefinitive plumages of males across species. Here, we provide the first full review of the natural history of manakin predefinitive plumages as the basis for qualitatively addressing the six major hypotheses about the production and function of predefinitive plumages. We find little evidence to support the possibilities that manakin predefinitive plumages are directly constrained by inflexible molt schedules, resource limitations to definitive coloration, or hormonal ties to reproductive behaviors. There is little evidence that could support a crypsis function, although direct experimentation is needed, and mimicry is refuted except for one unusual species in which predefinitive males sire young. Instead, evidence from a handful of well-studied species suggests that predefinitive plumages help young males explicitly signal their social status, and thereby gain entry to the social hierarchies which dictate future reproductive success. Our conclusions are especially influenced by the unique fact that males of at least 11 species throughout the family exhibit multiple predefinitive plumage stages with distinctively male patches. For each hypothesis, we highlight ways in which a better knowledge of female and young male birds offers critical opportunities for the use of manakins as a model clade.
... We can imagine several scenarios that provide testable hypotheses for relationships between preformative molt and behavioral ecology in Neotropical birds. For example, virtually all woodcreepers (Dendrocolaptinae) exhibit complete preformative molts, and subsequent formative plumages are strikingly similar to their juvenal plumages (Johnson and Wolfe 2017), suggesting that formative plumages (2008), Howell (2010), and Wolfe et al. (2014). ...
... Here, we follow the Wolfe et al. (2014) definition that "definitive" is used only to describe plumages derived from definitive molt cycles (second or later molt cycle for the majority of species). Definitive molt cycles are defined as having molts with counterparts in subsequent cycles. ...
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The slow-paced life history of many Neotropical birds (e.g., high survival and low fecundity) is hypothesized to increase lifetime fitness through investments in self-maintenance over reproduction relative to their temperate counterparts. Molt is a key investment in self-maintenance and is readily shaped by environmental conditions. As such, variation in molt strategies may be a key mechanism underlying life-history trade-offs and adaptation to new environments. Here, we review molt strategies from a diversity of lowland Neotropical landbirds and examine how variation in molt strategies, characterized by differences in molt insertions, timing, extent, and duration contribute to life-history variation and adaptation to diverse ecological conditions. In addition to our synthesis, we present a case study to examine the relationship between home range size and duration of the definitive prebasic molt of a well-studied subset of Amazonian landbirds. Our results suggest a connection between prolonged molt duration and larger home range size of small-to-medium-sized Amazonian landbirds. Our aims were to identify key gaps in our knowledge of Neotropical bird molt, to stimulate further comparative studies into the evolution of molt strategies, and to highlight how variation in molt strategies may be a key mechanism underlying life-history variation across latitudes.
... The annual, complete molt all birds undergo is termed the prebasic molt and generates the basic plumage. In addition to the prebasic molt, many species of birds undergo a second molt within their annual cycle, termed the prealternate molt, which generates the alternate plumage and typically corresponds to what is colloquially known as the breeding plumage (Wolfe, Johnson, & Terrill, 2014). The prealternate molt varies broadly in presence and extent among taxa, as well as the amount of phenotypic change it produces. ...
... In some species, extent of molt and dichromatism differs between the first prealternate molt and definitive prealternate molts. In these cases, we considered only the definitive prealternate molts (Wolfe et al., 2014). We scored molt extent using the same museum and literature resources, through examination of molt limits (Pyle, 1997a). ...
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Many species of birds show distinctive seasonal breeding and nonbreeding plumages. A number of hypotheses have been proposed for the evolution of this seasonal dichromatism, specifically related to the idea that birds may experience variable levels of sexual selection relative to natural selection throughout the year. However, these hypotheses have not addressed the selective forces that have shaped molt, the underlying mechanism of plumage change. Here, we examined relationships between life‐history variation, the evolution of a seasonal molt, and seasonal plumage dichromatism in the New World warblers (Aves: Parulidae), a family with a remarkable diversity of plumage, molt, and life‐history strategies. We used phylogenetic comparative methods and path analysis to understand how and why distinctive breeding and nonbreeding plumages evolve in this family. We found that color change alone poorly explains the evolution of patterns of biannual molt evolution in warblers. Instead, molt evolution is better explained by a combination of other life‐history factors, especially migration distance and foraging stratum. We found that the evolution of biannual molt and seasonal dichromatism is decoupled, with a biannual molt appearing earlier on the tree, more dispersed across taxa and body regions, and correlating with separate life‐history factors than seasonal dichromatism. This result helps explain the apparent paradox of birds that molt biannually but show breeding plumages that are identical to the nonbreeding plumage. We find support for a two‐step process for the evolution of distinctive breeding and nonbreeding plumages: That prealternate molt evolves primarily under selection for feather renewal, with seasonal color change sometimes following later. These results reveal how life‐history strategies and a birds' environment act upon multiple and separate feather functions to drive the evolution of feather replacement patterns and bird coloration.
... The WRP system uses molt and plumage terminology originally proposed by Humphrey and Parkes (H-P), which is based upon how molts evolved along ancestral or in some cases recent bird lineages, rather than on contemporary and often plastic factors such as their seasonal timing, location, or extent (Pyle 2013a, Wolfe et al. 2014, Howell and Pyle 2015. Unlike traditional molt and plumage nomenclatures, the WRP system is equally applicable to birds in both temperate and tropical regions, irrespective of the timing and location of molts relative to those of breeding. ...
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Determination of a bird’s age or cohort is critical for studies on avian demography, occurrence patterns, behavior, and conservation management. Age designations have largely been developed in north-temperate regions and utilize calendar-based or seasonally based codes; however, in tropical regions and in the southern hemisphere, these coding systems have limited utility at best. To address these issues, we had previously devised the “WRP system,” based on the nomenclature of Humphrey and Parkes (H–P) and Howell et al., which defines molts in an evolutionary context applicable to birds globally. Here we refine and build upon core concepts and definitions of the WRP coding system, resolving key limitations that were identified during its first decade of use. The WRP system employs a three-letter alpha code in which each letter describes a different aspect of H–P terminology: the molt cycle (which informs a bird’s age) and molt and plumage status within the cycle (each of which can also inform age). Here we recommend the continued use of most of the original (“core”) WRP coding while augmenting the system with an optional adjunct-code entry for comprehensiveness, clarity, and flexibility, and we clarify a few additional codes to cover less common molting and plumage strategies. For most users, from 7 to 13 core and 1 adjunct WRP code will be sufficient to describe all plumages and provide molt status and ages for demographic studies or other purposes. The revised WRP system is flexible enough to be adapted to the specific goals of programs while also providing core codes that can facilitate the comparison of avian age, molt, and plumage status on a global basis. We anticipate that our revised and standardized version of the WRP system will be easily adopted and could eventually replace calendar-based and seasonally based coding.
... Terminologies. Progress in understanding molt faces unfortunate obstacles because of differences in terminology (Wolfe et al. 2014, Howell and Pyle 2015, Jenni and Winkler 2020. Life cycle terms, which are generally used throughout Europe, Asia, and Africa, categorize molt relative to reproduction (e.g., post-breeding molt). ...
... T. schwierige Terminologie bis heute noch Uneinigkeit: "This, like molt itself, is a function of evolution" . Zwei Modelle konkurrieren miteinander: In den USA wird bei der Zählung der Kleiderfolge strikt auf Homologien geachtet; in Europa orientiert sich die Benennung pragmatisch am Jahreszyklus (basierend auf Dwight 1900;Humphrey & Parkes 1959;Amadon 1966;E & V Stresemann 1966;Howell et al. 2003;Jenni & Winkler 1994, 2004Wolfe et al. 2014). ...
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Oskar Heinroth, Erwin Stresemann, and a short history of the study of moult The unifying characteristic of all birds is the feathers, which consist of keratin. They enable flight but are subject to abrasion and wear, which necessitates that they must be renewed regularly by moulting. Moult is an energy-intensive process without which a bird cannot survive. It is all the more astonishing that it has aroused little interest among ornithologists. A simple, but perhaps not completely wrong explanation attributes this to "an aversion to messy birds" (Howell 2003). Even at the beginning of the 20th century it was questioned that changes in the body feathers are caused by moulting. Instead, even prominent ornithologists believed the process to be a change of colour. Oskar Heinroth (1871-1945) and Erwin Stresemann (1889-1972) are two ornithologists who enthusiastically studied the process of moult throughout their lives and who made important contributions to moult research. For Heinroth, the so-called "change of colour theory" was the trigger for his interest in moult, while for Stresemann it was the careful examination of study skins. They came into contact as early as 1907, when Stresemann was 18 years old, and their scientific exchange only ended with Heinroth's death. In their final working years, Erwin Stresemann and his wife Vesta (1902-2004) devoted themselves intensively to the study of moult. The results are summarized in their work "Die Mauser der Vögel", which they dedicated to Oskar Heinroth (Stresemann 1966). These two prominent ornithologists are rightly regarded as pioneers of moult research. Their studies and lifelong scientific exchange contributed significantly to the establishment of this branch of ornithology. Both Heinroth and Stresemann recognised early on the bewildering variability of moulting strategies, which depends more on ecological than phylogenetic factors, and left many open questions for modern moult research. Since the 1960s the number of moult-related publications has increased considerably, bringing important new insights into ornithology. This development is briefly described. Today's innovative techniques have long since provided answers that go far beyond those of the early researchers.
... We are quite aware that our descriptions of moult lack the precision typically demanded by students of moult. Indeed, moult terminology continues to divide researchers otherwise eager to describe moult variation in an evolutionary framework (Humphrey and Parkes 1959;Rohwer et al. 1992;Howell et al. 2003;Wolfe et al. 2014). ...
A verbal model from 1937 proposed that the darkness of the nest cavity acts as a proximate trigger for the simultaneous moult observed in female hornbills. Although never tested, the plausibility of this hypothesis has allowed it to be cited frequently. We tested the role of darkness on the moult of Tockus hornbills by providing females with either opaque wooden nest boxes or translucent plastic ones. Most females underwent a simultaneous moult of their remiges and retrices following clutch completion, regardless of the amount of time they had spent in the nest. More importantly, the variation in the simultaneity of the flight feather moult was unrelated to box type. These results suggest that darkness does not act as a proximate cue for the simultaneous moult of female hornbills.
The timing of events in birds’ annual cycles is important to understanding life history evolution and response to global climate change. Molt timing is often measured as an index of the sum of grown feather proportion or mass within the primary flight feathers. The distribution of these molt data over time has proven difficult to model with standard linear models. The parameters of interest are at change points in model fit over time, and so least-squares regression models that assume molt is linear violate the assumption of even variance. This has led to the introduction of other nonparametric models to estimate molt parameters. Hinge models directly estimate changes in model fit and have been used in many systems to find change points in data distributions. Here, we apply a hinge model to molt timing, through the introduction of a double-hinge (DH) threshold model. We then examine its performance in comparison to current models using simulated and empirical data. Our results suggest that the Underhill–Zucchini (UZ) and Pimm models perform well under many circumstances and appear to outperform the DH model in datasets with high variance. The DH model outperforms the UZ model at low sample sizes of birds in active molt and shorter molt durations and provides more realistic confidence intervals at smaller sample sizes. The DH model provides a novel addition to the toolkit for estimating molt phenology, expanding the conditions under which molt can accurately be estimated.
For decades, ecologists have studied fundamental questions of how Amazonian biodiversity is maintained, and whether that diversity can persist following deforestation. The long history of avian research at the Biological Dynamics of Forest Fragments Project, near Manaus, Brazil, has helped advance this understanding in the context of a broader research program focused on rainforest fragments embedded in a dynamic matrix. By sampling birds beginning before fragments were isolated, in the late 1970s, and continuing the protocol to the present, our work has revealed community dynamics driven not just by area and isolation, but also by larger landscape patterns, particularly second growth recovery over decadal scales. Fragments permanently lose some bird species, but their communities need not follow a trajectory toward catastrophic change. Our challenge now is to determine under what conditions remnant patches and developing second growth can support not just the rich diversity of Amazonian rainforest species but also their population processes and emergent community properties.
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All birds have fundamentally similar patterns of plumage succession. Thus Humphrey and Parkes (1959) proposed a system of nomenclature (the H-P system), based on homologies, that has become standard for molt studies in North America. However, presumably analogous similarities in pattern between first basic and definitive basic plumages have obscured homologies. Many plumages conventionally known as “first basic” are better considered as novel first-cycle plumages that lack homologous counterparts in subsequent cycles. Consequently, current nomenclature does not consistently reflect between-species homologies. Howell and Corben (2000b) proposed that traditional juvenal plumage can be considered an unambiguous starting point for a terminology that better reflects presumed homologies in basic plumages; alternate and other nonbasic plumages may not necessarily be homologous between species. Four underlying strategies of increasing complexity incorporate all known patterns of plumage succession: the Simple Basic Strategy, the Complex Basic Strategy, the Simple Alternate Strategy, and the Complex Alternate Strategy. We review inconsistency in the H-P system; explain the four underlying strategies; and discuss how one can identify homologies (if any) between plumages in first and subsequent cycles and among taxa. Many species have novel plumages added into their first plumage cycle; we argue that existing terminology for these plumages is unsuitable and we term them formative plumages attained by preformative molts. Finally, we provide examples of how this modified H-P system can be applied to diverse taxa of birds while reflecting the homology underlying all basic plumage cycles. Our revision validates the flexibility and utility of the H-P system. El Problema del Primer Plumaje Básico: Una Revisión de las Homologías de la Muda y del Plumaje Resumen. Todas las aves tienen patrones de sucesión del plumaje fundamentalmente similares. De este modo, Humphrey y Parkes (1959) propusieron un sistema de nomenclatura (el sistema H-P), basado en homologías, el cual ha sido de uso común en estudios de muda de plumaje en Norte América. Sin embargo, supuestas similitudes análogas entre el primer plumaje básico y el plumaje definitivo básico han confundido las homologías. Muchos plumajes convencionalmente conocidos como “primer básico” son considerados mejor como plumajes originales del primer ciclo que carecen de contrapartes homólogas en los ciclos siguientes. Consecuentemente, la nomenclatura actual no refleja las homologías entre especies. Howell y Corben (2000b) propusieron que el tradicional plumaje juvenil puede ser considerado como un punto de partida inequívoco para una terminología que refleje mejor las homologías presuntas en los plumajes básicos; los plumajes alternos y otros plumajes no básicos pudieran no ser homólogos entre especies. Cuatro estrategias de creciente complejidad incorporan todos los patrones conocidos de sucesión de plumajes: La Estrategia Básica Simple, La Estrategia Básica Compleja, La Estrategia Alterna Simple, y La Estrategia Alterna Compleja. Examinamos ciertas inconsistencias en el sistema H-P; explicamos las cuatro estrategias subyacentes, y discutimos cómo se pueden identificar homologías (cuando existen) entre los plumajes del primer ciclo y de los ciclos siguientes, y entre taxa diferentes. Muchas especies tienen plumajes originales adicionales en su primer ciclo de plumaje; sostenemos que la terminología actual para estos plumajes es inadecuada y los denominamos como plumajes formativos, logrados por mudas preformativas. Finalmente, damos ejemplos de como este sistema H-P modificado puede ser aplicado a diversos tipos de aves y al mismo tiempo reflejar la homología subyacente a todos los ciclos de plumajes básicos. Nuestra revisión valida la flexibilidad y utilidad del sistema H-P.
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Adult birds replace their flight feathers (moult) at least once per year, either in summer after termination of breeding or (in the case of some long-distance migratory species) in the winter quarters. We reconstructed the evolutionary pathways leading to summer and winter moult using recently published molecular phylogenetic information on the relationships of the Western Palearctic warblers (Aves: Sylviidae). Our phylogenetic analysis indicates that summer moult is the ancestral pattern and that winter moult has evolved 7–10 times in this clade. As taxa increased their migratory distance and colonized northern breeding areas, summer moult disappeared and winter moult evolved. Our data also allows us to trace the historical origins of unusual moult patterns such as the split-moult and biannual moult strategies: the most parsimonous explanations for their origins is that they evolved from ancestral states of summer moult. We briefly discuss our results in the light of recent criticisms against phylogenetic comparative methods and the utility of historical versus functional definitions of adapation.
The recent paper by Howell et al. (2003) recognizes that birds have evolved special plumages before entering the adult plumage cycle that should, therefore, be named differently in the terminology introduced by Humphrey and Parkes (1959) for plumages and molts (the H-P system). We agree with the principle of this suggestion, but we nevertheless suggest that birds take different lengths of time and different numbers of molts to enter the adult molt cycle and to acquire the adult plumage. We suggest that this variation should not be concealed by the assumption of an artificial first cycle of the same length as subsequent cycles, but should be reflected in the terminology of plumages and molts. We also suggest a distinction between entering the adult molt cycle and entering the adult plumage cycle. A main problem of the H-P system and Howell et al.'s modification is the claim that it is based on the concept of homology. In our opinion, there are no firm and convincing criteria on which to base a plausible phylogeny of plumages and molts. We would prefer to call Howell et al.'s modified H-P system a “terminology” for molts and plumages without the claim to determine homologies. We suggest that plumages or molts having the same Howell et al. term should be called “comparable,” rather than homologous. Moreover, it is debatable whether the phylogeny of molt is always the same as the phylogeny of plumages, as the H-P system claims by linking one molt to one plumage. We believe that the H-P system and Howell et al.'s modification of it remains too rigid to adequately reflect the evolution of molts and plumages. El Problema de las Homologías de la Muda y el Plumaje y el Primer Ciclo del Plumaje Resumen. El artículo reciente de Howell et al. (2003) reconoce que las aves han desarrollado a través de la evolución plumajes especiales que ocurren antes del ciclo del plumaje adulto y que deberían, por lo tanto, tener un nombre diferente en la terminología introducida por Humphrey y Parkes (1959) para los plumajes y las mudas (el sistema H-P). Nosotros estamos de acuerdo con el principio de esta sugerencia, pero sin embargo sugerimos que las aves toman diferentes períodos de tiempo y diferentes números de mudas para entrar al ciclo de muda adulto y para adquirir el plumaje adulto. Sugerimos que esta variación no debería ser enmascarada por la suposición de un primer ciclo artificial de la misma longitud de los ciclos subsecuentes, sino que debería reflejarse en la terminología de plumajes y mudas. También sugerimos una distinción entre entrar al ciclo de muda adulto y entrar al ciclo de plumaje adulto. Un problema principal del sistema H-P y de la modificación de Howell et al. es la idea de que están basados en el concepto de homología. Nuestra opinión es que no existen criterios firmes y convincentes sobre los cuales basar una filogenia plausible de los plumajes y las mudas. Preferiríamos tratar al sistema H-P modificado por Howell et al. como una “terminología” para mudas y plumajes, sin pretender determinar homologías. Sugerimos que los plumajes o las mudas que tienen el mismo término en el sistema de Howell et al. deberían llamarse “comparables” en lugar de homólogos. Más aún, es debatible si la filogenia de la muda es siempre igual a la filogenia de los plumajes, como el sistema H-P asevera al conectar una muda con un plumaje. Creemos que el sistema H-P y la modificación de Howell et al. son todavía demasiado rígidos para reflejar adecuadamente la evolución de la muda y los plumajes.
Forty-five years ago Humphrey and Parkes (1959) introduced their system of nomenclature for molts and plumages (the H-P system). They claimed that their biologically neutral terminology, independent of the bird's life cycle events, could accurately reflect homologies of molts and plumages across a wide range of avian taxa. Soon, however, several investigators reported trouble adapting the terminology to unusual sequences of molts and plumages, and others expressed doubts that it could accurately reflect true phylogenetic homologies. Howell et al. (2003) reviewed these problems and proposed a modification of the original H-P system that identifies the juvenal plumage as the first basic plumage, and any postjuvenal plumages that are not repeated in later plumage cycles as formative plumages. By doing this, they solved the problem of adapting the original H-P system to plumages of the first year of life in many species. However, they have not overcome the arguments of Stresemann (1963) and Amadon (1966) that patterns of molting and plumage are so variable, and so subject to natural selection, that there is doubt that the H-P terminology can reveal phylogenetic homologies even among closely related species. Molting and plumage sequences within a clade comprising four species of the genus Carduelis confirm that within this limited grouping, molting and plumages are highly variable, and apparent homologies are not revealed in the H-P terminology as modified by Howell et al. La Terminología de la Muda y el Plumaje de Howell et al. (2003) Podría no Reflejar Aún las Homologías Resumen. Hace cuarenta y cinco años, Humphrey y Parkes (1959) introdujeron su sistema de nomenclatura para la muda y el plumaje (el sistema H-P). Ellos sugirieron que su terminología biológicamente neutra, independiente de los eventos del ciclo de vida de las aves, podría reflejar con exactitud las homologías de la muda y el plumaje a través de un amplio espectro de taxa. Sin embargo, poco después varios investigadores notaron problemas al adaptar la terminología a secuencias inusuales de muda y plumajes, y otros expresaron dudas en cuanto a si podría reflejar con exactitud las verdaderas homologías filogenéticas. Howell et al. (2003) revisaron estos problemas y propusieron una modificación del sistema H-P original que identifica el plumaje juvenil como el primer plumaje básico, y cualquier plumaje post-juvenil que no se repita en ciclos posteriores del plumaje como plumaje formativo. Haciendo esto, solucionaron el problema de adaptar el sistema H-P original a plumajes del primer año de vida de muchas especies. Sin embargo, no lograron resolver las críticas de Stresemann (1963) y Amadon (1966) de que los patrones de muda y plumaje son tan variables y tan propensos a ser afectados por selección natural, que es dudoso que la terminología H-P pueda revelar homologías filogenéticas, aún entre especies estrechamente relacionadas. Las secuencias de muda y plumaje al interior de un clado formado por cuatro especies del género Carduelis confirman que dentro de este limitado grupo, la muda y el plumaje son áltamente variables y que algunas homologías aparentes no son reveladas por la terminología H-P con las modificaciones de Howell et al.
We studied the pattern and timing of prebasic molt in adult Gray Catbirds (Dumetella carolinensis) at two New England sites: Block Island, Rhode Island (BIRI), and the Vermont Institute of Natural Science (VINS) in Woodstock, Vermont. Catbirds at VINS initiated molt earlier and molted at a significantly slower rate than catbirds at BIRI. Mean individual molt durations spanned approximately 54 days at VINS and 44 days at BIRI. The two groups ended molt at about the same time. Catbirds at VINS were more variable in the timing of their molt. At both sites, second-year catbirds began and ended molt significantly earlier than after second-year catbirds. Males and females did not differ significantly in their rate or timing of molt at either site. Behavioral observations at BIRI indicated that catbirds spent less time foraging during the heaviest period of molt, but that increased foraging during late molt stages coincided with increases in fat stores, indicating overlap of molt and hyperphagy. We found no evidence that Gray Catbirds at either site departed for migration prior to completing remigial molt. The later molt schedule of BIRI birds likely resulted from the extended breeding season of some individuals. We believe that molt schedules at the two sites were influenced less by latitude per se than by site-specific differences in vegetation, food abundance, and temperature, resulting from differing elevations and conditions of coastal and inland environments.