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Avian molt, or the regularly scheduled replacement of feathers, is an important life history event, particularly in central Amazonian rainforest birds for which a relatively high proportion of the annual cycle can be dedicated to this process. Here, we detail molt strategies of 18 antbird species (Thamnophilidae) based on 2,362 individuals captured from lowland tropical rainforest at the Biological Dynamics of Forest Fragmentation Project near Manaus, Brazil. All species exhibited a molt strategy consistent with the Complex Basic Strategy, in which birds undergo an inserted preformative molt within the first cycle, but apparently lack prealternate molts. The preformative molt and resulting formative plumage aspect of the 18 antbird species can be grouped by three distinct patterns: 1) a complete molt resulting in an adult-like formative plumage without molt limits; 2) a partial molt involving body feathers, lesser coverts, at least some or all median and greater coverts, and sometimes tertials or rectrices, resulting in an adult-like formative plumage with molt limits; and 3) a partial molt as in ‘2’ but resulting in an adult female-like formative plumage in both sexes with plumage maturation delayed in males until the second prebasic molt. In addition, we show that one species, Percnostola rufifrons, exhibited an extra inserted molt (a partial auxiliary preformative molt) in the first cycle before initiating a complete preformative molt making this, to our knowledge, the first description of an auxiliary preformative molt for a suboscine. The extent of the preformative molt or delayed plumage maturation was not predicted by ecological guild, raising questions about how phylogenetic relatedness and ecological adaptation drive variation in molt patterns across antbirds.
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Thamnophilidae (antbird) molt strategies in a central
Amazonian rainforest
Source: The Wilson Journal of Ornithology, 126(3):451-462.
Published By: The Wilson Ornithological Society
DOI: http://dx.doi.org/10.1676/13-163.1
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THAMNOPHILIDAE (ANTBIRD) MOLT STRATEGIES IN A CENTRAL
AMAZONIAN RAINFOREST
ERIK I. JOHNSON
1,2,3,4
AND JARED D. WOLFE
1,2
ABSTRACT.—Avian molt, or the regularly scheduled replacement of feathers, is an important life history event,
particularly in central Amazonian rainforest birds for which a relatively high proportion of the annual cycle can be
dedicated to this process. Here, we detail molt strategies of 18 antbird species (Thamnophilidae) based on 2,362 individuals
captured from lowland tropical rainforest at the Biological Dynamics of Forest Fragmentation Project near Manaus, Brazil.
All species exhibited a molt strategy consistent with the Complex Basic Strategy, in which birds undergo an inserted
preformative molt within the first cycle, but apparently lack prealternate molts. The preformative molt and resulting
formative plumage aspect of the 18 antbird species can be grouped by three distinct patterns: 1) a complete molt resulting in
an adult-like formative plumage without molt limits; 2) a partial molt involving body feathers, lesser coverts, at least some
or all median and greater coverts, and sometimes tertials or rectrices, resulting in an adult-like formative plumage with molt
limits; and 3) a partial molt as in ‘2’ but resulting in an adult female-like formative plumage in both sexes with plumage
maturation delayed in males until the second prebasic molt. In addition, we show that one species, Percnostola rufifrons,
exhibited an extra inserted molt (a partial auxiliary preformative molt) in the first cycle before initiating a complete
preformative molt making this, to our knowledge, the first description of an auxiliary preformative molt for a suboscine.
The extent of the preformative molt or delayed plumage maturation was not predicted by ecological guild, raising questions
about how phylogenetic relatedness and ecological adaptation drive variation in molt patterns across antbirds. Received 4
October 2013. Accepted 1 March 2014.
Key words: auxiliary preformative molt, delayed plumage maturation, molt cycle, preformative molt, understory
insectivore.
The durability, aerodynamic capability, and
thermoregulatory properties of feathers undoubt-
edly contributed to the global proliferation of
birds. Despite the importance of feather mainte-
nance through regular replacement, or molt,
ornithological interest has disproportionately been
focused on other phases of the life cycle such as
migration and breeding (Bridge 2011). Given that
the timing, speed, and extent of molts have
cascading effects on the entire avian life cycle,
documenting variation in molt strategies among
species is a necessary step towards understanding
factors that contributed to the evolution of
plumage coloration, migration, and courtship
behaviors among other aspects of the avian cycle
(Humphrey and Parkes 1959; Rohwer et al. 1980,
2005; Svensson and Hederstro¨m 1999). In gener-
al, molt strategies have been well documented in
North American and European taxa (Svensson
1992; Baker 1993; Mulvilhill 1993; Jenni and
Winkler 1994; Pyle 1997, 2008; Howell 2010),
whereas similar work in the Neotropics is still in
its infancy (reviewed in Ryder and Wolfe 2009;
see also Ryder and Dura˜es 2005; Guallar et al.
2009; Wolfe et al. 2009a, b; Herna´ndez 2012).
The antbirds (Passeriformes: Thamnophilidae,
sensu Remsen et al. 2014) are members of a diverse
family of suboscines with about 220 species
confined to the New World tropics and subtropics
(Zimmer and Isler 2003). Antbirds are relatively
well studied among Neotropical birds, ranging
from the detailed life history descriptions by Willis
(1969, 1973), to recent phylogenetic analyses
(Brumfield et al. 2007, Moyle et al. 2009, Bravo
et al. 2012), to community assembly analyses
(Go´mez et al. 2010), but their molt strategies have
received little attention. From what is known,
antbirds apparently follow the Complex Basic
Strategy, in which an inserted extra molt, the
preformative molt (sensu Howell et al. 2003),
occurs in the first cycle of a bird’s life and ranges in
extent among species from partial to complete,
although details of the preformative molt in many
species have yet to be described (Ryder and Wolfe
2009). Partial molts involve body feathers and
some wing coverts, but not flight feathers, resulting
in two generations of plumage, and the boundary
between retained juvenal and replaced formative
1
School of Renewable Natural Resources, Louisiana
State University and Louisiana State University Agricul-
tural Center, Baton Rouge, LA 70803, USA.
2
Projecto Dinaˆ mica Biolo´gica de Fragmentos Florestais,
Instituto Nacional de Pesquisas da Amazoˆ nia, Avenue
Andre´ Araujo 2936, Petro´polis, Cep 69083-000, Cp. 478,
Manaus, Amazonas, Brazil.
3
Current address : National Audubon Society, 6160
Perkins Road, Suite 135, Baton Rouge, LA 70808, USA.
4
Corresponding author; e-mail: ejohnson@audubon.org
The Wilson Journal of Ornithology 126(3):451–462, 2014
451
feathers is referred to as a ‘molt limit’ (sensu Pyle
1997).
Plumage maturation is an import aspect of the
preformative molt in many passerines, as this
process exchanges a juvenile plumage with a
more adult-like plumage. Plumage color is driven
by endogenous hormonal signals refined through
adaptive necessities or constraints, and the
development and deposition of these pigments
presumably represent tradeoffs between factors
such as energetic cost, social status, and predation
risk (Murphy 1996, Hill and McGraw 2006).
Delaying plumage maturation until after the
formative plumage is a strategy employed by a
wide variety, albeit a minority, of temperate and
tropical passerines, perhaps most famously among
manakins (Pipridae) but also among a variety of
other migratory suboscines and oscines (e.g.,
Thompson 1991, McDonald 1993, Hill 1996,
Saetre and Slagsvold 1996). Delayed plumage
maturation is often considered an adaptation to a
social consequence in which not advertising
maturity is adventitious (reviewed in Hawkins et
al. 2012). Unfortunately, the frequency and role of
delayed plumage maturation within the diverse
antbird family has not been systematically
examined.
What drives variation in the extent of pre-
formative molts in antbirds? In diverse predom-
inantly temperate passerine families such as
Sylviidae, Parulidae or Emberizidae, more exten-
sive preformative molts are common among
species living in harsh environments characterized
by dense vegetation or increased daily exposure to
ultraviolet light. This relationship probably re-
flects an adaptation in which the juvenile plumage
lacks the structural integrity necessary to carry-on
day-to-day activities (thermoregulation, flight,
etc.) and needs to be quickly replaced by an
extensive formative plumage (Dwight 1900,
Willoughby 1991, Jenni and Winkler 1994, Pyle
1998, Svennson and Hedenstro¨m 1999, Howell
2010, Small et al. 2013). Exposure to ultraviolet
light may not be particularly problematic for
antbird species that frequent tropical forest
understories, with the exception of gap specialists,
when compared to migratory temperate species
that are exposed to more hours of sunlight
throughout the annual cycle. Other factors such
as understory vegetation density, distance traveled
(ant-following birds commonly travel long dis-
tances), and foraging behavior (sallying versus
terrestrial insectivores) may exert increased deg-
radation pressures to juvenile feathers and neces-
sitate a more extensive preformative molt extent
in antbirds.
In this study, we examine preformative molt
variation within a community of rainforest,
understory-dwelling antbirds from the central
Amazon. More specifically, we describe variation
in the preformative molt within and among
species, and describe whether this molt results in
delayed plumage maturation (i.e., a juvenile or
female-like formative plumage in males). After
assigning study species to one of four ecological
guilds, we discuss whether these guilds are useful
predictors of preformative molt characteristics.
METHODS
We captured birds with mist-nets (NEBBA type
ATX, 36-mm mesh, 12 32 m) from 2007–2012 in
continuous and fragmented primary rainforest at
the Biological Dynamics of Forest Fragmentation
Project (BDFFP), ,80 km north of Manaus,
Amazonas, Brazil (2.5uS, 60uW). Mist-nets were
placed at ground level in lines of 4, 8, or 16
depending on the site and were open between 0600
and 1400 Amazon Time (AMT) (see Bierregaard et
al. 2001 and Stouffer et al. 2006 for details). We
sampled primarily during the dry season from June
to December; while this may initially appear
seasonally limiting for assessing molt strategies,
most antbirds at the BDFFP breed and molt in any
month of the year (Johnson et al. 2012, Stouffer
et al. 2013) providing an opportunity to see all
potential age and sex classes and their intermedi-
ates during our field season.
There are 28 species of Thamnophilidae known
to occur at the BDFFP (Cohn-Haft et al. 1997). We
report molt strategies in 18 understory species for
which we have adequate samples, excluding three
mid-story/canopy species and seven locally rare
species (Cohn-Haft et al. 1997, Johnson et al.
2011a). Captured birds were banded and examined
for active molt or molt limits, skull ossification,
and soft-part colors. When molt limits were
suspected, we described the extent of the molt in
each feather tract, such as how many greater
coverts, rectrices, tertials, primaries, and second-
aries were replaced versus retained. Digital images
of open wings (e.g., Fig. 1) were also taken to
analyze and document molt patterns. Given high
capture rates during our banding operations, not all
data were recorded from each bird when fast
processing was necessary to ensure bird safety.
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THE WILSON JOURNAL OF ORNITHOLOGY NVol. 126, No. 3, September 2014
We assessed the extent of preformative molts
using two criteria. First, we looked for clear
evidence of mixed juvenile and adult-like (i.e.,
formative) feathers in all birds whether molting
or not. Juvenile feathers in Thamnophilidae are
distinct from subsequent plumages by having
loosely textured feathers with lower barb densities
than in subsequent plumages, having distinct
coloration, and having distinct shapes with
rectrices being more pointed and longer, greater
coverts being shorter, and remiges being shorter
(Dwight 1900, Zimmer and Isler 2003). Second,
we looked for molt limits in birds that were not
molting that appeared consistent in extent among
other individuals of the same species. We follow
Pyle (1997) and define a molt limit as an
interruption in a molt episode that is arrested,
i.e., the molt does not continue later but starts over
at the next episode. We recorded details of the
numbers of feathers replaced in relevant feather
tracts, including the greater coverts, secondaries,
primaries, primary coverts, and rectrices, as well
as the presence or absence of molt limits among
median coverts. For sexually dichromatic species
(i.e., all species with the exception of Pithys
albifrons), we also noted whether the resulting
formative plumage aspect was adult-female-like
or adult-male-like.
We also evaluated other criteria for aging birds,
which was helpful to assign observations of active
FIG. 1. Representative images of first cycle birds with incompletely ossified skulls, including two species going
through complete preformative molts (A, B) and two species with molt limits resulting from a partial preformative molt (C,
D). A) Pithys albifrons, sex unknown, with p1–2 replaced, p3 growing, p4–10 juvenile; B) Percnostola rufifrons, male, with
three generations of feathers including juvenile (five outer greater coverts, primary coverts, secondaries, and primaries),
female-like auxiliary formative (lesser and median coverts), and adult-male-like formative (four median coverts and two
greater coverts); C) Hypocnemis cantator, male, with molt limits among the greater coverts (the outer five greater coverts,
carpal covert, primary coverts, secondaries, and primaries are retained from the juvenile plumage); D) Myrmotherula
longipennis, sex unknown, with molt limits among the greater coverts (the inner four are replaced/formative and the outer
five are retained/juvenile; the carpal covert, primaries and secondaries are also retained from the juvenile plumage).
Johnson and Wolfe NAMAZONIAN ANTBIRD MOLT STRATEGIES
453
molt or molt limits into age brackets. First, we
looked for changes in soft-part colors, such as in
the iris, bill, or tarsus, and determined when
particular species reached an adult-like color
relative to the molt status. Second, we examined
skulls for ossification, which often completes in
passerines between six and eight months of age,
before the second prebasic molt initiates (Nero
1951, Pyle 1997). To our knowledge, no detailed
account of skull ossification timing exists for
antbirds, but ossification is believed to complete
or nearly complete in a similar timeframe as
found in other passerines (Capparella et al. 1997,
Isler et al. 1997, Tallman and Tallman 1997,
Zimmer and Isler 2003).
We categorized each species into an ecological
guild that represents foraging strategy and habitat
use, following Stouffer et al. (1995). These guilds
included obligate mixed-species flock members,
gap or disturbed-forest specialists, obligate ant-
followers, and other understory insectivores
(Table 1).
RESULTS
We accumulated 3,859 captures representing
2,764 individual antbirds after 48,898 mist-net hours
of effort, ultimately aging 2,362 individuals (85.5%;
Appendix A). We found that all 18 study species
followed a Complex Basic Strategy. Preformative
molts grouped into three distinct patterns (Table 1):
1) complete, resulting in an adult-like formative
plumage (Fig. 1a, b); 2) partial, with replaced adult-
like body feathers, lesser coverts, at least some or all
median and greater coverts, and sometimes tertials
or rectrices in both sexes (Fig. 1c); and 3) partial, as
in ‘2’ but always resulting in an adult female-like
formative plumage in both sexes with plumage
maturation delayed in males until the second
prebasic molt (Fig. 1d). In species with complete
preformative molts, the skull always ossified during
the preformative molt, sometime between the
replacement of primary 1 and 6 (Fig. 2, Table 2),
whereas in species with partial preformative molts,
i.e., not involving flight feather replacement, the
skull ossified after the completion of the preforma-
tive molt (Table 2).
Five of 18 study species showed a complete
preformative molt (Table 1). In these species, the
resulting formative plumage was essentially
identical to subsequent definitive basic plumages
(i.e., ‘adult’-like). One species, P. albifrons, was
sexually monochromatic and the other four were
sexually dichromatic in the formative and defin-
itive basic plumages. We concluded that these
complete post-juvenile molts were consistent with
a preformative molt (sensu Howell et al. 2003)
using four criteria. First, continuous body and
wing molt always followed a distinct juvenile
plumage. Second, an interrupted molt that was
consistent with a partial or incomplete molt was
not observed or predominant in these species.
Third, soft-part colors, such as iris color (in
Gymnopithys rufigula,Frederickena viridis,
Thamnophilus punctatus, and Percnostola rufi-
frons) and tarsus color (in P. albifrons) transi-
tioned into an adult-like coloration before com-
pletion of the post-juvenile molt. Finally, we
examined the timing of skull ossification in P.
albifrons,G. rufigula, and P. rufifrons and found
that it completed between the replacement of
primary 1 and 6 (Table 2, Fig. 2).
The remaining 13 study species showed molt
limits resulting from a partial preformative molt
(Table 1). Multiple individuals of these species
showed similar molt limits among the median
coverts, greater coverts, tertials, and/or rectrices,
and there was no evidence for more extensive or
complete preformative molts in these species
(Table 2). In some species (e.g., Thamnomanes
caesius), more feathers were replaced in the
median and greater coverts, on average, than in
other species (e.g., Epinecrophylla gutturalis).
Similarly the frequency and extent of tertial and
rectrix replacement was greater in some species,
particularly those that replaced more greater
coverts (Table 2). In five of these species, we
were able to recapture at least one individual that
retained the identical molt limit for at least 15 days
and up to 186 days later (Appendix B), confirming
that molt limits were not the result of actively
molting birds or molt suspensions. In all species,
we found that the skull had completely ossified
before the second prebasic molt initiated, and in
seven species we found individuals with molt
limits with either ossified or incompletely ossified
skulls, suggesting the skull ossified during or
shortly after completion of the preformative molt
(Table 1).
In all 13 species with partial preformative
molts, the second (definitive) basic plumage was
sexually dichromatic, but in only nine of these
were replaced formative plumage feathers in both
sexes similar to subsequent definitive basic
counterparts. The remaining four species exhibit-
ed delayed plumage maturation in males with the
formative plumage appearing adult female-like;
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THE WILSON JOURNAL OF ORNITHOLOGY NVol. 126, No. 3, September 2014
TABLE 1. The percentage of individuals with unossified skulls (and number of individuals examined) in each age category (following Wolfe et al. 2010, Johnson et al. 2011b)
indicating the timing of skull ossification. In all species (with one exception*), the skull ossifies before the initiation of the SPB/DPB, i.e., during the FCF in species with partial
preformative molts and during the FPF in species with complete preformative molts (see also Fig. 2). Also indicated is the ecological guild for each species (A 5understory
insectivore; B 5gap or disturbed-forest species; C 5ant-follower; D 5obligate mixed-flock member).
Age Category
Species Guild FPJ or FCJ FPF FCF FAJ SPB DCB DPB
Complete preformative molt
Frederickena viridis A - - 0.0 (11) -
Thamnophilus punctatus B - - 0.0 (1) -
Percnostola rufifrons B - 31.6 (19) 0.0 (12) 0.0 (9)
Pithys albifrons C 100.0 (11) 51.3 (39) 1.8
a
(56) 0.0 (11)
Gymnopithys rufigula C 100.0 (5) 36.4 (11) 0.0 (29) 0.0 (5)
Partial preformative molt – sexually dichromatic
Thamnophilus murinus B - - 20.0 (5) - 0.0 (8) 0.0 (1)
Thamnomanes ardesiacus D - 100.0 (1) 20.0 (10) 0.0 (7) 0.0 (29) 0.0 (2)
Thamnomanes caesius D - - 4.8 (21) 0.0 (3) 0.0 (19) 0.0 (3)
Isleria guttata A - - - - - 0.0 (2)
Epinecrophylla gutturalis D 100.0 (1) - 81.3 (16) - 0.0 (7) 0.0 (1)
Myrmotherula axillaris B - - 0.0 (9) 0.0 (3) 0.0 (6) 0.0 (1)
Hypocnemis cantator B - 100.0 (1) 11.1 (9) 0.0 (2) 0.0 (23) 0.0 (1)
Myrmeciza ferruginea A - 100.0 (3) - - 0.0 (3) 0.0 (2)
Hylophylax naevia A - - - - 0.0 (2) -
Partial preformative molt – delayed plumage maturation
Myrmotherula longipennis D - - 0.0 (6) 0.0 (6) 0.0 (28) 0.0 (3)
Myrmotherula menetriesii D - - 100.0 (2) 0.0 (2) 0.0 (6) -
Schistocichla leucostigma B 100.0 (1) 100.0 (1) 66.7 (3) 0.0 (2) 0.0 (3) -
Willisornis poecilinota A - 100.0 (1) 23.5 (17) 0.0 (12) 0.0 (26) 0.0 (10)
a
Skull was estimated to be 90%ossified in one individual.
Johnson and Wolfe NAMAZONIAN ANTBIRD MOLT STRATEGIES
455
FIG. 2. The relationship between ossification and feather molt of primaries in three species with complete preformative
molts: a) Pithys albifrons;b)Gymnopithys rufigula;c)Percnostola rufifrons.
456
THE WILSON JOURNAL OF ORNITHOLOGY NVol. 126, No. 3, September 2014
the adult male plumage aspect was not acquired
until the second prebasic molt.
In one species, P. rufifrons, an apparent extra,
or third, molt in its first cycle was noted, which
we call an auxiliary preformative molt following
Howell et al. (2003), also referred to as a
presupplemental molt by Rohwer (1986), Thomp-
son (1991), and Pyle (1997). In this species, this
partial molt replaced juvenile body, lesser coverts
and some median coverts with adult female-like
feathers in both sexes, and was quickly followed
by a sexually dichromatic complete preformative
molt that initiated before the skull ossified
(Fig. 2c, Table 1). Therefore, three generations
of feathers were apparent on birds early in the
preformative molt, which was particularly obvi-
ous in males (Fig. 1b). The skull ossified before
this complete molt concluded, similar to other
antbird species with complete preformative molts
(Fig. 2, Table 1).
Preformative molt strategies were not appar-
ently associated with ecological guild as all three
preformative molt strategies were utilized by
multiple ecological guilds (Table 1). Each of the
three preformative molt strategies was observed
in three of four guilds. Only the obligate ant-
follower guild aligned with one preformative molt
strategy, but there were only two species to
consider in this guild.
DISCUSSION
All 18 species of antbird that we examined
appeared to follow a molt strategy that was
consistent with the Complex Basic Strategy and
preformative molts were variable in extent across
species, as indicated by Ryder and Wolfe (2009).
Although we could not conclusively eliminate the
possibility of an undetected prealternate molt in
this study, it seems unlikely that prealternate
molts exist in these species, as few other resident
tropical forest species apparently exhibit prealter-
nate molts (Howell et al. 2003, Ryder and Wolfe
2009). Complete wing molts in these antbirds can
take 155 days (M. menetriesii) to 301 days (P.
albifrons), leaving little time in an annual cycle to
insert additional molts, although molt cycles may
not be annual in some ant-followers (e.g., P.
albifrons, J. Chaves-Campos, pers. comm., John-
son et al. 2012), and prealternate molts have a
potential to overlap protracted preformative or
definitive prebasic molts. Because individuals of
antbirds at the BDFFP can molt or breed at any
time year (Johnson et al. 2012, Stouffer et al.
TABLE 2. The number of replaced feathers (range, median, and absolute median deviation [MAD]) in four different feather tracts during partial preformative molts and the
number of individuals examined (n) for 13 species of Thamnophilidae.
Median coverts: Greater coverts: Tertials: Rectrices:
Species %with limits (n) Range (n) Median 6MAD Range (n) Median 6MAD Range (n) Median 6MAD
Thamnophilus murinus 0.0 (2) 2–9 (3) 3 61 0 (2) 0 60 0 (1) 0 60
Thamnomanes ardesiacus 9.1 (11) 1–9 (22) 6 63 0–2 (15) 1 60 0 (3) 0 60
Thamnomanes caesius 40.0 (15) 0–9 (34) 6 62 0–3 (20) 2 61 0–6 (9) 0 60
Isleria guttata 100.0 (1) 5 (1) 5 60 2 (1) 2 60 0 (1) 0 60
Epinecrophylla gutturalis 37.5 (16) 0–8 (19) 0 60 0 (16) 0 60 0 (4) 0 60
Myrmotherula axillaris 0.0 (12) 1–9 (17) 4 62 0–3 (13) 0 60 0 (4) 0 60
Myrmotherula longipennis 0.0 (2) 1–9 (5) 3 62 0–1 (4) 0 60 0 (3) 0 60
Myrmotherula menetriesii 0.0 (1) 3 (1) 3 60 0 (1) 0 60- -
Hypocnemis cantator 8.3 (12) 0–8 (17) 3 62 0–1 (14) 0 60 0–1 (7) 0 60
Schistocichla leucostigma 0.0 (3) 1–6 (4) 4 61 0 (3) 0 60 0 (2) 0 60
Myrmeciza ferruginea 0.0 (5) 8–9 (5) 8 60 0 (5) 0 60 0 (3) 0 60
Hylophylax naevia 100.0 (1) 1–5 (2) 3 62 0 (1) 0 60- -
Willisornis poecilinota 0.0 (8) 0–9 (23) 3 61 0–3 (9) 0 60 0 (6) 0 60
Johnson and Wolfe NAMAZONIAN ANTBIRD MOLT STRATEGIES
457
2013), distinguishing body molts from other
scheduled molts and adventitious feather replace-
ment would require an in-depth examination of
body feather tracts using recaptured birds. Our
data indicate that partial prealternate molts
involving wing coverts or tertials, at least, do
not occur.
To our knowledge, P. rufifrons is the first
suboscine described to have an auxiliary prefor-
mative molt inserted between the juvenile and
formative plumages in the first cycle. An
alternative explanation for what we call the
auxiliary preformative molt (sensu Howell et al.
2003) in P. rufifrons is that this is instead a partial
preformative molt that results in a female-like
plumage, which is then followed by a complete
second (definitive) prebasic molt, a strategy
exhibited by Myrmotherula longipennis,Myr-
motherula menetriesi,Willisornis poecilinota,
and Schistocichla leucostigma. In this scenario,
the second prebasic molt would begin while the
skull is incompletely ossified (Fig. 2c), suggesting
an advancement of the second prebasic molt by at
least six months. This idea was also posed as an
alternative for explaining Ruby-throated Hum-
mingbird molts (P. Pyle, in Cardiff and Dittmann
2009), and such a dramatic temporal advancement
of the second prebasic molt would represent a
novel strategy for molt in birds. We instead
suggest that this inserted partial first-cycle molt in
P. rufifrons is indeed an auxiliary preformative
molt and that the subsequent complete molt is a
preformative molt, based on consistencies with
complete preformative molts in other antbirds.
First, the skull ossified during the complete molt,
consistent with the other species that exhibited a
complete preformative molt. Second, the iris
transitioned from a juvenile brown color to an
adult red (in males) or orange (in females) color
during this complete molt, comparable to soft-part
transitions in other antbird species with complete
preformative molts. Third, the plumage resulting
from the partial molt was never observed for more
than a few weeks before it began transitioning into
the next complete molt, unlike the plumages
resulting from partial preformative molts that
often lasted months in other species.
It was perhaps surprising that four of our 18
study species showed delayed plumage matura-
tion, a phenomenon not well-documented in
Thamnophilidae (Zimmer and Isler 2003). A
number of hypotheses have been proposed to
explain delayed plumage maturation in other
birds, particularly for independent subadults of
temperate migratory species (reviewed in Thomp-
son 1991) and lekking species (Foster 1987,
McDonald 1993, Ancia˜es and Del Lama 2002,
Ryder and Dura˜es 2005). These hypotheses are
founded on explanations related to the social
environment (Hawkins et al. 2012), such as the
juvenile mimicry hypothesis (Lawton and Lawton
1986, Foster 1987) and summer female mimicry
hypothesis (Rohwer et al. 1980), but slight
modifications to these hypotheses may be neces-
sary when considering non-lekking resident trop-
ical species. Our antbird study species maintain
year-round territories held by an often sexually
monogamous male-female pair, thus breeding
is expected to be reserved for territory-holding
individuals (Stutchbury and Morton 2001, Zim-
mer and Isler 2003).
In non-lekking resident Neotropical species
with delayed plumage maturation, we hypothesize
that delayed plumage maturation may correlate
with delayed natal dispersal. Interestingly, we
have observed brood patches during the formative
plumage in several species that do not undergo
delayed plumage maturation, such as Thamno-
manes and E. gutturalis, suggesting they disperse
from their natal territory and at least attempt to
breed in territories of their own within their first
cycle of life. To the contrary, in all four species
that show delayed adult male plumage acquisi-
tion, we have not observed brood patches in
formative-plumaged birds. From these observa-
tions, we postulate that the acquisition of adult-
like male feathers during the preformative molt
may be linked to hormonal signals that facilitate
breeding in the first cycle, and certainly further
study is needed to corroborate this. Non-exclusive
mechanisms related to delayed natal dispersal and
delayed plumage maturation in antbirds may
include assisting with rearing offspring (as in
some Australian fairy-wrens; Schodde 1982),
remaining on natal territories to increase lifetime
fitness and fecundity, or life-history traits result-
ing in breeding territory saturation. The hypoth-
esized relationship between delayed breeding or
territory acquisition and delayed plumage matu-
ration should be tested with data on the timing of
natal dispersal relative to the preformative molt in
antbirds, along with an exploration of mechanisms
that may help drive these patterns.
Molt strategies may be adaptive and optimized
in response to drivers that include environmental
conditions, migration strategy, and social require-
458
THE WILSON JOURNAL OF ORNITHOLOGY NVol. 126, No. 3, September 2014
ments (Rohwer et al. 2009, Howell 2010). Here,
we show substantial variation in preformative
molt strategies of non-migratory birds occurring
in similar habitats, from a single location, and
within a single taxonomic family. The observed
variation in molt presents an interesting opportu-
nity to relate these strategies to other life history
traits, relatively independent of environmental
conditions; however, preformative molt strategies
did not align with our classifications of ecological
guilds with three of four guilds represented in
each of three preformative molt strategies. It may
be that ecological guilds per se are less important
than explicit measures of the density of vegetation
and exposure to ultraviolet light – unfortunately
measurements of these environmental conditions
in occupied habitat-space do not exist for these
species. As an exception, complete preformative
molts were found in both species of ant-followers,
an ecological category confounded with taxonom-
ic relatedness as all obligate ant-following ant-
birds cluster within the Pithyini Tribe (Brumfield
et al. 2007, Moyle et al. 2009). A complete
preformative molt resulting in an ‘‘adult-like’’
plumage has also been described in other ant-
followers including Rhegmatorhina gymnops
(Willis 1969) and Phaenostictus mcleannani
(Willis 1973), suggesting complete preformative
molts are wide-spread and shared among ant-
followers, posing the question whether complete
preformative molts among obligate ant-followers
is a result of phylogenetic inertia, convergence on
optimized strategy for ant-following, some other
factor, or all of the above.
Although we assessed molts in fewer than 10%
of the Thamnophilidae species, our results suggest
that preformative molt patterns may not necessarily
be phylogenetically conserved, with perhaps the
exception of ant-followers (Brumfield et al. 2007,
Moyle et al. 2009). For example, in two species of
Thamnophilus, one showed a complete preforma-
tive molt whereas the other showed a partial
preformative molt. In the five ‘antwren’ species
(Myrmotherula,Isleria, and Epinecrophylla), all
showed partial preformative molts but with differ-
ent levels of plumage aspect maturation. Among
the closely-related Percnostola,Schistocichla,and
Myrmeciza, respective preformative molts were
complete, partial with delayed plumage maturation
in males, and partial and sexually dichromatic.
Only once molt and plumage strategies are
described in other antbirds, can advances in under-
standing their population biology be realized, which
is particularly critical as these Neotropical species
face increased habitat alteration in the coming
decades. This large and ecologically diverse family
may also be a particularly interesting model for
examining functional and evolutionary mechanisms
that drive variation in molt strategies across species.
Revealing these patterns might help elucidate
adaptive responses to social, ecological, and
evolutionary forces and lead to a more comprehen-
sive understanding of avian life histories.
ACKNOWLEDGMENTS
We would like to thank our field assistants for their
dedication and hard work to help capture birds, particularly
J. Lopes, C. F. Vargas, S. M. de Freitas, F. C. Diniz, and
T. Straatmann. Logistical support from the staff of the
Biological Dynamics of Forest Fragmentation Project
(BDFFP) and support by M. Cohn-Haft and G. Ferraz at
Brazil’s Instituto Nacional de Pesquisas da Amazoˆnia
(INPA) and the Smithsonian Institute made this research
possible. Funding was provided by the U.S. National Science
Foundation acquired by P. C Stouffer (LTREB-1257340).
Helpful comments by P. C Stouffer and two anonymous
reviewers have improved the quality of this manuscript. This
is publication 637 of the BDFFP Technical Series and
number 31 in the Amazonian Ornithology Technical Series
of the INPA Zoological Collections Program. This manu-
script was approved for publication by the Director of the
Louisiana Agricultural Experimental Station as manuscript
number 2014-241-14051.
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APPENDIX A. The number of individuals in each age category captured/recaptured near Manaus, Brazil for 18 species
of Thamnophilidae grouped by preformative molt strategy. FPJ 5first prejuvenile molt; FCJ 5first cycle juvenile
plumage; FPF 5first preformative molt; FCF 5first cycle formative plumage; SPB 5second prebasic molt; DCB 5
definitive cycle basic plumage; DPB 5definitive prebasic molt; FAJ 5after juvenile plumage (age codes follow Wolfe et
al. 2010, Johnson et al. 2011b).
Species FPJ or FCJ FPF FCF SPB DCB DPB FAJ
Partial preformative molts – sexually dichromatic
Thamnophilus murinus 0/0 1/0 8/0 4/1 34/5 10/1 -
Thamnomanes ardesiacus 7/0 4/0 33/3 39/5 120/26 34/5 -
Thamnomanes caesius 6/0 5/0 68/2 35/4 94/21 28/1 -
Isleria guttata 0/0 0/0 1/0 2/0 1/0 3/1 -
Epinecrophylla gutturalis 4/0 2/0 27/1 4/0 62/6 20/4 -
Myrmotherula axillaris 0/0 2/0 32/4 17/1 51/7 18/3 -
Hypocnemis cantator 3/0 3/0 31/2 13/0 82/17 22/1 -
Myrmeciza ferruginea 2/0 4/0 9/0 1/0 23/6 15/2 -
Hylophylax naevia 1/0 0/0 2/0 0/0 3/0 0/0 -
Partial preformative molts – delayed plumage maturation
Myrmotherula longipennis 2/0 2/0 15/0 20/3 77/12 26/2 -
Myrmotherula menetriesii 0/0 0/0 5/0 12/3 40/2 7/0 -
Schistocichla leucostigma 1/0 1/0 6/0 4/0 14/1 4/0 -
Willisornis poecilinota 2/0 3/0 63/11 38/11 156/37 82/24 -
Complete preformative molts
Frederickena viridis 0/0 3/0 - - - 3/0 18/3
Thamnophilus punctatus 0/0 1/1 - - - 0/0 2/0
Percnostola rufifrons 2/0 57/7 - - - 53/10 87/18
Pithys albifrons 93/8 211/38 - - - 168/26 218/41
Gymnopithys rufigula 14/0 25/1 - - - 20/2 123/26
Johnson and Wolfe NAMAZONIAN ANTBIRD MOLT STRATEGIES
461
APPENDIX B. Individuals with molt limits (indicating formative plumage) recaptured at least 15 days later with
identical molt limits near Manaus, Brazil.
Species Individual Days between captures
Thamnomanes caesius E34895 49
E44087 18
Epinecrophylla gutturalis D95268 128
Myrmotherula axillaris E49364 186
C43752 40
C38335 28
C38336 28
Hypocnemis cantator 4H6455 181
D93777 42
Willisornis poecilinota E44116 119
E43839 40
E79385 33
E128621 24
E44082 18
E44123 16
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THE WILSON JOURNAL OF ORNITHOLOGY NVol. 126, No. 3, September 2014
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Molting is an important process of birds’ natural history and learning about molt and plumage allows a better understanding of various aspects of birds’ life. In temperate zones, knowledge about molt strategy, type of plumage characteristics and their association with age are well documented. In contrast, knowledge about molt in Neotropical birds is not well developed. One species with numerous studies regarding molt in several localities is the widely-distributed Rufous-collared Sparrow (Zonotrichia capensis). These studies covered various localities along the species range, facilitating comparisons among populations, and providing an excellent model for the study of plumage and molt variation. In this study, I described both molt strategy and extent of molt Z. capensis costaricensis, through sampling data for one year at two localities in Bogotá city. I captured and banded Z. capensis individuals and collected information about characteristics such as molt limits, skull ossification and iris coloration, which allow for the identification of molt/plumage type and its relation to age categories of a cycle-based age classification system. I found that Z. capensis has a complex basic strategy, where all prebasic molts, including prejuvenal molt, are complete and the preformative molt is a partial molt. The results are congruent with previous findings for this species in some areas. Nevertheless, the molt varies largely in Z. capensis across its distribution and individuals out of Neotropics have an additional partial-incomplete prealternate molt and it is still unknown why.
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Work on the publication date of Bonnaterre & Vieillot’s Tableau encyclopédique et méthodique calls into question the priority of some names in use today. Among these Myrmothera guttata Vieillot, 1824, proves to be a junior synonym of a name introduced earlier. The possible reversal of precedence is studied here in compliance with the International Code of Zoological Nomenclature.
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Research Proposal
Boasting with 1640 bird species, Ecuador is known worldwide for its high diversity in bird species. But despite the high species richness and endangerment of its avian fauna, ornithological research in Ecuador is still scarce. Especially certain biogeographic regions, like the humid forests of the Ecuadorian Chocó, are very poorly documented. One of the many challenges for field biologists is the enormous lack of baseline information on avian life cycle events, such as molt and breeding. Molt strategies and patterns are unknown for many resident bird species, making it difficult to reliably determine age and gender of birds in the field. In 2014, I started a long-term avian monitoring project at Un poco del Chocó nature reserve in the Andean Chocó. In my doctoral research I will investigate the avian life cycle phenology of a community of landbirds in the Andean Chocó. I will capture birds on a monthly basis and document molt and breeding events over the course of three annual cycles together with food abundance and climate, in order to determine the timing, duration, intensity and interrelatedness of these two life cycle events in relation to climatically-influenced variables. This study will therefore contribute substantially to our knowledge and understanding of the life cycle events of the threatened bird community of the Andean Chocó. Furthermore, I will examine the utility of different ageing and sexing criteria for the bird species of the Andean Chocó that have not previously been described. With the determination of reliable criteria to identify age and sex of birds in the field, I hope to lay the foundations for further demographic research and science-driven conservation planning.
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Background Vast areas of lowland neotropical forest have regenerated after initially being cleared for agricultural purposes. The ecological value of regenerating second growth to forest-dwelling birds may largely depend on the age of the forest, associated vegetative structure, and when it is capable of sustaining avian demographics similar to those found in pristine forest. Methods To determine the influence of second growth age on bird demography, we estimated the annual survival of six central Amazonian bird species residing in pristine forest, a single 100 and a single 10 ha forest fragment, taking into consideration age of the surrounding matrix (i.e. regenerating forest adjacent to each fragment) as an explanatory variable. Results Study species exhibited three responses: arboreal, flocking and ant-following insectivores ( Willisornis poecilinotus , Thamnomanes ardesiacus and Pithys albifrons ) showed declines in survival associated with fragmentation followed by an increase in survival after 5 years of matrix regeneration. Conversely, Percnostola rufifrons , a gap-specialist, showed elevated survival in response to fragmentation followed by a decline after 5 years of regeneration. Lastly, facultative flocking and frugivore species ( Glyphorynchus spirurus and Dixiphia pipra , respectively) showed no response to adjacent clearing and subsequent regeneration. Conclusions Our results in association with previous studies confirm that the value of regenerating forest surrounding habitat patches is dependent on two factors: ecological guild of the species in question and second growth age. Given the rapid increase in survival following succession, we suggest that the ecological value of young tropical forest should not be based solely on a contemporary snapshot, but rather, on the future value of mature second growth as well.
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We studied molt patterns and age determination based on molt limits, plumage criteria, and skull ossification for the Blue‐and‐yellow Tanager (Pipraeidea bonariensis), a passerine that is commonly distributed along the western slope of the Peruvian Andes. Through careful examination of live individuals in the hand and museum specimens, we suggest that P. bonariensis exhibits a complex alternate strategy with partial preformative and prealternate molts during its first cycle, a complete definitive prebasic molt, and presumably a partial definitive prealternate molt starting with its second cycle. We established the age in 68% of captured individuals using the skulling technique. Most individuals of P. bonariensis were recorded with fully ossified skulls during their preformative molts, whereas some adults in basic plumage had retained small, unossified windows. Our results corroborate those reported for related Neotropical taxa and provide important guidelines that facilitate an accurate and rapid technique for aging and sexing Neotropical tanagers in the hand, an essential requirement in demographic studies and long‐term banding projects.
Thesis
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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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Molt patterns and sex and age criteria for five resident landbird species from the Colombian Andean zone are presented. This information was gathered throughout 12 months of field work in the Reserva Forestal Protectora Regional de Bitaco, and visits to Museo de Ornitologia of Universidad del Valle, Colombia. Partial to incomplete preformative molts, and complete prebasic molts were found for all species, similar to related taxa in temperate zones. Prealternate molts were detected for one species (Tangara vitriolina), while presupplemental molts remained undetected. Morphological differences between sexes were not observed, therefore its use is not recommended when sexing these birds. Age determination is possible thanks to the presence or absence of differences in quality, shape, and wear between juvenal and formative feathers, produced by partial or incomplete preformative molts; similar to the system used in temperate latitudes.
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Amazonian forest bird communities are among the richest in the world. Even so, relatively little is known about the organization of the entire avian community at local scales or about differences across Amazonia. These are fundamental data not only for understanding the processes generating and maintaining tropical diversity, but also as a baseline for evaluating anthropogenic changes to Amazonian forests. Here we provide a description of the entire bird community for a 100 ha plot of terra firme forest at the Biological Dynamics of Forest Fragments Project, near Manaus, Brazil, based on spot-map and mist net surveys augmented by additional field and analytical techniques. Although our results are from a single plot surveyed in a single year, our methods and interpretation reflect nearly 30 years of ornithological research at the site. We found 228 species on the plot, of which 207 were considered part of the core regional avifauna. Median density was five individuals/100 ha. Only 13 species (6% of the core species) had densities ≥ 20 individuals on the plot, although 55 species (27%) had ≤ 2 individuals. No species had territories smaller than 3 ha; median territory size was 11 ha for the 103 species for which we could make reasonable estimates. Measured by numbers of species or individuals, the plot was dominated by insectivores (54% of species, 62% of individuals). Biomass, however, was dominated by frugivores and granivores (59%). Compared to available data from other Amazonian forests, our site appears to have comparable richness of a similar set of species, but lower density and greater patchiness. Our results suggest that the area required to support populations of many species will be even greater in central Amazonia than in western Amazonia.
Article
Long-tailed manakins (Chiroxiphia linearis) and swallow-tailed manakins (C. caudata) are closely related, sexually dichromatic, lek-breeding species in which male mating success is highly skewed. Males of both species delay plumage maturation. Before reaching the definitive state, they wear a sequence of feather coats less conspicuous than that of the adult. Nondefinitive plumages probably enhance male survival in the two species; in C. caudata they may also enhance breeding success of young males, who may be fully reproductively mature their first year. In C. linearis testicular development is retarded along with that of plumage, although males may be physiologically capable of breeding prior to the acquisition of the definitive plumage. This difference probably reflects differences in the social systems of the two species. Five hypotheses have been proposed to explain the evolution of delayed plumage maturation. The sexual-selection, cryptic-breeder, and winter-adaptation hypotheses suggest that it functions primarily to enhance survival of young males. The juvenile- and female-mimicry hypotheses emphasize enhancement of immediate mating success. Support is provided for all but the female-mimicry hypothesis; it is argued that data are more consistent with juvenile mimicry and a neotenic origin of nondefinitive plumages.
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First-year, but not adult, Indigo Buntings (Passerina cyanea) have a previously unknown supplemental plumage. The presupplemental molt includes all of the rectrices, the outermost but not the innermost primaries, and, typically, the three innermost secondaries and all body feathers. In this molt, young females exchange one adult-femalelike plumage for another, while young males exchange an adult-femalelike plumage for one that matches that of adult males in winter. Thus, in their first year Indigo Buntings wear: first, the juvenile plumage, the body feathers of which begin replacement before the tail is fully grown; second, the first basic plumage, which in both sexes is entirely femalelike in coloration and includes the juvenile remiges and rectrices; third, the supplemental plumage, assumed either prior to fall migration (<10% of individuals) or on the wintering ground (>90% of individuals) and in which obvious sexual dichromatism is first achieved; and fourth, the first alternate plumage, acquired in a prolonged and often incomplete prealternate molt of body feathers that occurs during February, March, and April on the wintering ground and during the spring in the United States. Because almost all of the femalelike first basic plumage of young males is lost in the presupplemental molt, this plumage almost certainly is an adaptation to conditions encountered either in the fall or early in the first winter. Furthermore, the ensuing supplemental plumage cannot be compromised by color requirements of the first breeding season because of the intervening prealternate molt; thus, the adult-malelike plumage produced by the presupplemental molt likely evolved to meet a change in signaling requirements that occurs in early winter. The signaling function of this plumage is unknown. Because this supplemental plumage of young males resembles the winter plumage of adult males and because all feathers grown by young males in their first prealternate molt resemble those of the adult male breeding plumage, the female mimicry hypothesis of Rohwer et al. (1980) is untenable for the subadult breeding plumage of yearling male Indigo Buntings.
Chapter
The nutrition of animals involves procurement of food, digestion and absorption of component nutrients, metabolism and (or) assimilation of absorbed nutrients, and elimination of resulting waste products. Adequate nutrition is essential to an organism’s survival and reproductive success (i.e., fitness). Determining what constitutes adequate nutrition for free-living animals poses a challenge. An animal’s nutritional status depends on (1) its nutrient needs, (2) nutrient accessibility, and (3) the metabolic, physiological, morphological, and behavioral plasticity that the animal can invoke either to avert or to minimize discrepancies between demand and accessibility, or to resolve conflicting demands through the course of its annual or life cycle (e.g., adaptive anorexias; Mrosovsky and Sherry 1980). This chapter focuses on these three elements of the nutritional budgets of birds. An exhaustive review of the literature germane to this topic is neither practical nor possible. This chapter is intended only to provide an overview and some direction for future research. For the sake of brevity, reviews and recent reports have been preferentially cited here. Two sources of notable value, because of their scope and attention to avian nutrition, are Scott et al. (1982) and Robbins (1993).