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The flight feather moult pattern of the bearded vulture (Gypaetus barbatus)

  • Estudios Medioambientales Icarus S.L.


Moult is an extremely time-consuming and energy-demanding task for large birds. In addition, there is a trade-off between the time devoted to moulting and that invested in other activities such as breeding and/or territory exploration. Moreover, it takes a long time to grow a long feather in large birds, and large birds that need to fly while moulting cannot tolerate large gaps in the wing, but only one or two simultaneously growing feathers. As a consequence, large birds take several years to complete a full moult cycle, and they resume the moult process during suboptimal conditions. A clear example of this pattern is the Bearded Vulture (Gypaetus barbatus), which needs 2–3 years for changing all flight feathers. Here we describe the sequence, extent, and timing of moult of 124 Bearded Vultures in detail for the first time. We found that extent and timing of flight feather moult was different between age classes. Subadults (from 3rd to 5th calendar year) started moult, on average, in early March, whereas adults only started moult, on average, in late April, possibly due to breeding requirements. Second calendar year individuals delayed onset of moult until the middle of May. In general, the moult lasted until November, and although adults started to moult later than subadults, they moulted more feathers. Subadults needed 3 years for moulting all flight feathers, whereas adults normally completed it in 2 years.
The flight feather moult pattern of the bearded vulture
(Gypaetus barbatus)
igo Zuberogoitia
Juan Antonio Gil
Enrique Martı
Birgit Erni
Bakartxo Aniz
Pascual Lo
Received: 27 February 2015 / Revised: 15 June 2015 / Accepted: 29 June 2015 / Published online: 14 July 2015
Ó Dt. Ornithologen-Gesellschaft e.V. 2015
Abstract Moult is an extremely time-consum ing and
energy-demanding task for large birds. In addition, there is
a trade-off between the time devoted to moulting and that
invested in other activities such as breeding and/or territory
exploration. Moreover, it takes a long time to grow a long
feather in large birds, and large birds that need to fly while
moulting cannot tolerate large gaps in the wing, but only
one or two simultaneously growing feathers. As a conse-
quence, large birds take several years to complete a full
moult cycle, and they resume the moult process during
suboptimal conditions. A clear example of this pattern is
the Bearded Vulture (Gypaetus barbatus), which needs
2–3 years for changing all flight feathers. Here we describe
the sequence, extent, and timing of moult of 124 Bearded
Vultures in detail for the first time. We found that extent
and timing of flight feather moult was different between
age classes. Subadults (from 3rd to 5th calendar year)
started moult, on average, in early March, whereas adults
only started moult, on average, in late April, possibly due
to breeding requirements. Second calendar year individuals
delayed onset of moult until the middle of May. In general,
the moult lasted until November, and although adults
started to moult later than subadults, they moulted more
feathers. Subadults needed 3 years for moulting all flight
feathers, whereas adults normally completed it in 2 year s.
Keywords Bearded Vulture Gypaetus barbatus Moult
sequence Underhill–Zucchini model
Die Flugfedermauser beim Bartgeier
Die Mauser ist ein extrem zeit- und energieaufwa
Vorgang fu
r große Vo
gel. Daru
ber hinaus gibt es einen
Konflikt zwischen der Zeit, die fu
r die Mauser aufgebracht
wird und derjenigen, die in ander e Aktivita
ten investiert
werden kann, so wie Bru
ten oder territoriale Exploration.
Außerdem braucht das Wachstum einer langen Feder bei
großen Vo
geln lange; und große Vo
gel, die darauf ange-
wiesen sind wa
hrend der Mauser zu fliegen, ko
nnen sich
keine gro
ßeren Lu
cken in den Flu
geln leisten, sondern nur
ein oder zwei gleichzeitig nachwachsende Federn. Als
Konsequenz braucht es mehrere Jahre, bis große Vo
einen vollen Mauserzyklus vollendet haben, und sie neh-
men die Mauser unter suboptimalen Bedingungen wieder
auf. Ein deutliches Beispiel fu
r dieses Muster ist der
Bartgeier (Gypaetus barbatus), der zwei bis drei Jahre
braucht fu
r einen kompletten Wechsel sei ner Flugfedern.
Hier beschreiben wir zum ersten Mal im Detail die
Abfolge, das Ausmaß und das Timing der Mauser von 124
Bartgeiern. Wir fanden, dass Ausmaß und Timing der
Communicated by F. Bairlein.
& In
igo Zuberogoitia
Estudios Medioambientales Icarus S.L. C/San Vicente, 8. 6
Planta, Dpto 8, Edificio Albia I, 48001 Bilbao, Bizkaia, Spain
n para la Conservacio
n del Quebrantahuesos, Plaza
San Pedro Nolasco 1, 4u F, 50001 Zaragoza, Spain
s Eagle Study and Conservation Group, Apdo,
4009, 30080 Murcia, Spain
Department of Statistical Sciences, Centre for Statistics in
Ecology, Environment and Conservation, University of Cape
Town, Rondebosch 7701, South Africa
Pl Dra Juana Garcı
a Orcoyen 5, 31012 Pamplona, Spain
Vertebrates Zoology Research Group, University of Alicante,
Apdo. 99, 03080 Alicante, Spain
J Ornithol (2016) 157:209–217
DOI 10.1007/s10336-015-1269-3
Flugfedermauser sich zwischen Altersklassen unterschied.
Subadulte (vom dritten bis fu
nften Kalenderjahr) begannen
die Mauser, im Durchschnitt, im fru
hen Ma
rz, wa
hrend die
Mauser der Adulten im Durchschnitt erst im spa
ten April
begann, mo
glicherweise aufgrund von Zwa
ngen im
Zusammenhang mit der Brut. Individuen im zweiten
Kalenderjahr verzo
gerten den Beginn der Mauser bis Mitte
Mai. Generell dauerte die Mauser bis November, und
obwohl Adulte mit der Mauser spa
ter begannen als Sub-
adulte, mauserten sie mehr Federn. Subadulte brauchten
drei Jahre zur Mauser sa
mtlicher Flugfedern, wa
dagegen Adulte normalerweise in zwei Jahren fertig waren.
Large birds take a long time to complete a full cycle of life-
history stages. Normally, each stag e requires high amounts
of energy that determine mutual ly exclusive activities (e.g.
breeding, migration, and flight feather moult, Hedenstro
2006). In birds, the time required to raise young increases
with body size (Calder 1984), leaving large birds with less
time in their annual cycle for other activities (Rohwer et al.
2011). In long-distance migrants, flight feather moult rarely
overlaps with breeding or migration, but some species start
moulting during the last part of the bree ding season and
stop before migration, resuming the moult in winter
grounds (Herremans 2000; Chandler et al. 2010), whereas
others only moult once in the wintering areas (Barshep
et al. 2013). In contrast, sedentary large species can extend
the time devoted to moult, but suspend moult in winter to
save energy, in order to survive during adverse weather
periods and to obtain enough reserves to start reproduction
early (Zuberogoitia et al. 2013a). Hence, the more time
spent rearing young, the less time for moult, and, recip-
rocally, a longer moult that clears worn feather s from the
wing may make breeding in the next season impossible
(Rohwer et al. 2011).
Non-breeding birds have more time available for
moulting. However, for immature birds, time devoted to
moult is constrained by their inexperience (a poor knowl-
edge of the home range and thus decreased feeding effi-
ciency). On the other hand, experienced breeders take
advantage of their better knowledge of the territory,
allowing them to obtain resources more efficiently than
young birds (Espie et al. 2000; Daunt et al. 2007;
Zuberogoitia et al. 2013b; Penteriani et al. 2013). Hence,
adults optimize time and resources and, as a result, they can
moult more flight feathers in a given moult period and
quicker than inexperienced birds (Dietz et al. 2013;
Zuberogoitia et al. 2013a).
In some of the biggest flying birds, such as vultures,
condors, storks, and albatrosses, each moult cycle las ts
more than a year, but may be interrupted during difficult
periods, such as chick rearing, migration, or times of food
shortage, such as midwinter in high latitudes or during
extended droughts (Mundy 1982; Edelstam 1984; Clark
2004; Newton 2009). The moulting process places addi-
tional energy demands on birds (Hemborg and Lundberg
1998) in order to: (1) produce replacement plumage; (2)
regulate body temperature while feather insulation is
reduced; and (3) maintain efficient flight despi te gaps in the
wing due to dropped or growing feathers (Ginn and Mel-
ville 2000).
Feather growth rate in large birds is not much higher
than in small birds, but because feathers are much longer, it
takes longer to grow a long feather. Rohwer et al. (2009)
suggest that feather growth rate does not increase propor-
tional to feather size, but is constrained by one-dimensional
follicle size. Moreover, many large birds that depend on
flight for feed ing during moult, shed only a part of their
flight feathers annually and require two, and sometimes
three, years to complete moult (Rohwer et al. 2009). They
cannot tolerate large gaps in the wing, but can only tolerate
one or two simultaneously growing feathers. The replace-
ment of two or three adjacent remiges in quick succession
can lea ve large gaps in the wings inhibiting flight, so most
of these species have evolved strategies in which remiges
at different locations are replaced at the same time, pro-
ducing multiple smaller gaps while maintaining the wing’s
surface integrity and the bird’s ability to fly (Pyle 2006).
Moult duration is mainly determined by the number of
simultaneously growing feathers (Rohwer and Rohwer
2013). This strategy for replacing remiges among large
birds is known as ‘stepwise’ or ‘serial’ moult, and it is
also called ‘Staffelmauser’ (Stresemann and Stresemann
The Bearded Vulture, as other vultures, is a classic
example of a bird that has a serial/stepwise moult
(Staffelmauser; Houston 1975; Clark 2004; Zuberogoitia
et al. 2013a ). The moult pattern of the Bearded Vulture
(Gypaetus barbatus) has received little attention despite its
endangered status (see Margalida 2011). The species is
currently listed as ‘priority species in the conservation
strategies of the European Union (Birds Directive, Anne x
I) and is listed as ‘endangered’ in Spain (Antor et al.
2005). Hiraldo et al. (1979) documented a first approxi-
mation to the moult and later Adam and Llopis (2003)
described the flight feather moult in captive birds and in
free-ranging birds using photographs in flight. Later, Sese
(2011) published a summary of the moult pattern of
Bearded Vultures. Therefore, the aim of this paper is to
describe the moult pattern of the flight feathers of Bearded
210 J Ornithol (2016) 157:209–217
Vultures and analyse differences in the onset and duration
of moult between age groups.
A total of 153 Bearded Vultures of different ages [87
nestlings, 34 2nd calendar year (cy), 18 subadults, and 14
adults] and both sexes (86 males, 58 females, nine
unknown sex) were trapped, ringed, and tagged with wing-
tags from 1987 to 2014. Tags included an alphanumeric
code allowing individual identification at distance with
spotting scopes. This work took place as part of a long-term
conservation and research program conducted by FCQ
n para la Conservacio
n del Quebrantahuesos
in Spanish) in the central Pyrenees (Gil et al. 2010, 2014).
The number of trapped Bearded Vultures was limited
due to the small population size of the species in the
Pyrenees (i.e. 105 breeding units in Spain in 2010, Mar-
galida 2011; Gil 2012). Moreover, the endangered status of
this bird restricted the time devoted to obtain a correct
moult pattern because we were not allowed to hold them
long enough to score the moult of all trapped birds. Out of
the 66 completed moult sheets, we used 24 in the analysis.
The rest were excluded because we could not validate their
moult sheets with adequate photos. Moul t scores from six
dead, marked birds of known age from wildlife rehabili-
tation centres were also obtained.
In addition, 94 moult cards were obtained from high
definition (HD) and high quality pictures of wild birds taken
by wildlife photographers (see Snyder et al. 1987, Fig. 1, see
acknowledgements for photo credits). We compared series
of photos of each individual and used individual marks in
order to improve information about the moult.
Summarizing, we used 124 complete moult sheets: 11
1st cy, 25 2nd cy, 21 3rd cy, 15 4th cy, 18 5th cy, and 34
Number of feathers
The birds in hand were inspected following a standardized
protocol by one trained researcher (JAG). All birds were
photographed, and these pictures and those of the other non-
handled birds were inspected by a second trained researcher
(IZ, see Zuberogoitia et al. 2013a). We recorded a moult card
for both wings of each individual, identifying feather gen-
eration by wear, shape, colour, age pattern, and growth of the
remiges (i.e. primaries and secondaries) and rectrices. This
gave us data for 10 primaries (PP) and 19–20 secondaries
(SS) for each wing, and 12 rectrices (RR). For the moult
analysis, we only included the first 16 SS because we
observed that not all individuals had the expected 20 SS
(Adam and Llopis 2003): in four dead Bearded Vultures (two
first calendar year birds and two adults) with no active moult
in winter, the two juven ile birds had 19 SS, whilst the adults
had 20 SS, confirmed by removing all feathers to count the
insertion marks of SS in the ulna (forewing bone; Cieslak and
Bolestaw 2006). These results suggest an individual differ-
ential number of SS, possib ly due to the lack of one of the
innermost SS. Primaries were numbered in descending order
(from inside to outside), SS were numbered in ascending
order (from outside to inside) and RR were numbered cen-
trifugally (from the central feathers outwards).
Moult score
Following Ginn and Melville (2000) and Newton (2009)
we followed a standard recording system according to the
stage of growth of primaries and secondaries: old feathers
were scored as 0, fully grown new ones as 5, and growing
ones as 1–4 for intermediate stages of feather development.
These individual moult scores were then summed to give
an overall moult score between 0 and 50 (for 10 PP) and 0
and 80 (for 16 SS). Following Zuberogoitia et al. (2013a),
feathers scored as 0 were also recorded as A (juvenile), K
(moulted in the previous moult season), M (moulted
2 years ago), and O (moulted 3 years ago).
The extent of the moult at different age stages
In order to determine the extent of the moult for each age
class, we used birds checked at the end of the year, with no
active moult (some from the last days of November and
December), from which we considered all the feathers
scoring as ‘5’ and birds from the first months of the year
before the onset of the moult, considering all the feathers
scoring as ‘K’’.
Fig. 1 Example of HD picture from which a moult pattern can be
derived moult (picture by Bakartxo Aniz). This is a 4 cy bird recorded
on 18th November 2011. This bird had completed the moult of all the
flight feathers in 3 years. During 2011 it moulted P3, P4, P5, P9, and
P10 from both wings, S1, S4, S7-13 from the right wing, S1, S7-10,
S13-15 from the left wing and R3 and R5 from the tail feathers,
including R2 right, which was growing
J Ornithol (2016) 157:209–217 211
To calculate the symmetry of the moult process between
wings, we superimposed both wings and compared each
corresponding primary, secondary, and rectrix. We
assigned ‘1’ when both feathers were at the same moult
level and ‘0’ in those cases where the feathers were at a
different stage. We then summed up the scores of PP and
SS and calculated the perc entage of symmetry for the flight
feathers by comparing the sum to the total (see also
Zuberogoitia et al. 2005).
Timing of moult
We analysed timing of primary and secondary moult using
the models of Underhill and Zucchini (1988) and Underhill
et al. (1990), implemented in the ‘moult’ package (Erni
et al. 2013) for R (R Core Team 2014). These models give
estimates of moult duration and average start date (from
which average end date can be calculated) and also the
standard deviation of the start date. Because the number of
feathers moulted in a season differed between individuals,
it was not possible to calculate the proportion of feather
mass grown (the moult index used in the Underhill–Zuc-
chini models) in the current season. For this reason we used
the moult data type 1 (Underhill and Zucchini 1988),
requiring only the information whether an individual has
not yet started, is in moult, or has completed moult, coded
as 0, 0.5, and 1, respectively, only using the current year’s
moulting feathers for analyses. We used Julian day (Jan-
uary 1 = 1) as time scale in the analyses and graphs. We
classified individuals into three age groups: (1) Second cy:
birds in the second calendar year (cy) during their first
moulting season; (2) subadults: birds from 3cy to 5cy that
are still non-breeders (Lo
pez et al. 2013); and (3)
adults: birds from 6cy onwards with adult plumage (Sese
2011). Differences in start and duration of moult were
expected between the age groups. This was tested by
including age as a covariate on start and duration.
We ran three sets of models to estimate timing of moult
in PP, SS, and PP and SS combined. We compared models
using AIC, assuming models within two AIC units of the
best model to have similar support as the best model
(Burnham and Anderson 2002).
Modelling start and duration of moult
According to Underhill and Zucchini’s Models, the best
model for PP and PP&SS was M5 (Table 1). Models
improved when ‘age’ was considered as covariate. Start of
moult and standard deviation in start clearly differed
between age classes, and possibly duration differed
between ages when considering PP and SS combined
(model M4 was wi thin two units of AIC of the best model
M5). Most 2nd cy did not moult secondaries (Fig. 2).
Therefore, for secondaries, we fitted the moult models to
data including 2nd cy and then excluding 2nd cy.
Excluding 2nd cy, the null model was within two AIC units
of the best model (M2), showing that start and duration of
moult of SS did not clearly differ between subadults and
adults, although adults moult ed on average more SS than
subadults (Fig. 2).
Estimated average start of moult for subadult Bearded
Vultures was 3rd of March [Table 2 (PP&SS); Fig. 3],
whereas adults started on average on 26th of April. Second
cy birds delayed onset of moult until the 10th of May. The
duration of moult also differed between age groups. The
moult of PP finished before the SS (Table 2). In general,
the moult lasted until November (Fig. 3). Subadults had the
longest moult period (8 months) whilst 2nd cy were
moulting on average over a period of 6 months (Table 2).
Moult pattern
Second calendar year (2cy)
Bearded Vultures started moulting in their second cy. We
did not find evidence of flight-feather moult in any of the
11 first cy Bearded Vultures analysed between the fledging
season and the end of the year. There was no evidence of
moult in 2cy Bearded Vultures before May (n = 6), and
50 % of the analysed birds in May (n = 6) and 100 % of
birds in June (n = 5) had just dropped the P1. From then
until December, 2cy Bearde d Vultures moulted on average
4.32 inner primaries of each wing (SD = 1.25; range 3–6;
n = 25, Fig. 4). When the fourth primary was moulted, by
October, 2cy Bearded Vultures started to moult SS, nor-
mally S1, and rectrices, normally R1. Second cy Bearded
Vultures moulted on average only 0.58 SS (SD = 0.71;
range 0–2; n = 26, Fig. 4) of each wing and 0.56 RR
(SD = 0.71; range 0–3; n = 25) of each side of the tail.
The moulting process at this age showed a high degree of
symmetry (96.8 % in PP, 99.5 % in SS, and 96.67 % in
Third calendar year (3cy)
Bearded Vultures continued moulting PP, beginning
where they had left off in December of the previous
year, mainly P5, P6, and P7. We also detected 35 % of
birds beginning a new wave from P1. During the third
cy they replaced on average 3.75 PP of each wing
(SD = 0.97; range 2–5; n = 20). The moult of SS and
212 J Ornithol (2016) 157:209–217
RR started 2 or 3 weeks after start of primary moult.
During this period, 3cy birds moulted on average 5.78
SS (SD = 2.95; range 1–11; n = 19) and 2.55 RR of
each side of the tail (SD = 1.25, range 1–5, n = 18).
The moult of SS showed three foci: in S1, the starting
focus, which continued inwards in an orderly manner, in
S5 inwards, and in S15 towards both sides (Fig. 4).
These foci were observed in birds that showed the
neighbour feathers in sequential growing stages and
different birds showing the overlapping sequence (one
feather growing on the side of another new feather). Tail
feather moult als o showed different foci, starting in R1
outwards and following R6 inwards. We detected these
two foci in rectrices active at the same time in some
birds. The moulting process during the 3 cy still showed
a high degree of symmetry in PP (92.5 %), but sym-
metry was lower than in 2nd cy birds in SS (88.3 %)
and RR (82.5 %).
Table 1 Results of multi-
model evaluation applied to the
moult index of the Bearded
Model Duration | start | SD Type K AIC PP AIC SS AIC SS* AIC PP&SS
M1 1 | 1 | 1 1 3 (2) 139.4 206.0 142.3 136.0
M2 Age | 1 | 1 1 5 (4) 142.1 208.1 141.5 138.2
M3 Age | Age | 1 1 7 (6) 139.9 168.6 143.4 137.7
M4 Age | Age | Age 1 9 (6) 136.9 171.2 144.2 132.6
M5 1 | Age | Age 1 7 (6) 134.2 169.0 144.0 132.0
M6 1 | 1 | Age 1 5 (4) 140.7 187.3 142.5 135.2
Model ranking was assessed by Akaike information criteria (AIC). The models were fitted to four data sets:
primaries (PP), secondaries (SS), secondaries without 2nd cy birds (SS*), and all remiges (PP&SS). The
best model is marked in bold. The number of parameters is different (in parentheses) for the model of SS*
SD standard deviation in start date, K number of parameters
Fig. 2 Box plots of total moult
scores for primaries and
secondaries per age category.
All sampled birds were
considered for performing this
Table 2 Duration (days), start date, and standard deviation in start
date (days) estimates for each age class obtained from the M4 models
for primaries (PP) and primaries and secondaries (PP&SS)
Duration (SE) Start (SE) SD in start (SE)
2nd cy 166.4 (21.1) May 17th (10.1) 24.9 (16.3)
Subadults 184.7 (30.4) March 3rd (22.5) 80.6 (35.0)
Adults 143.0 (24.8) April 27th (18.8) 48.4 (23.3)
2nd cy 184.2 (13.2) May 10th (6.3) 13.2 (10.1)
Subadults 239.0 (33.7) March 6th (22.3) 79.5 (36.8)
Adults 216.1 (39.9) April 26th (27.6) 76.5 (41.0)
SE standard error
Fig. 3 Observed moult index (0, not started; 0.5, actively moulting;
1, moult completed for season) for moult in primaries and secondaries
of Bearded Vultures versus date (Julian days). The lines represent
estimated moult trajectories of the three age classes obtained with
model M4, starting at the mean start date, ending at mean end date
J Ornithol (2016) 157:209–217 213
Fig. 4 Moult pattern of
Bearded Vultures. The pattern
shows the most frequently
moulted primaries and
secondaries in second, third,
fourth, and fifth calendar years.
The feathers moulted in the
current season are black, those
moulted in the previous year are
grey and those which have not
been moulted are white. Moult
foci and moult direction are
indicated by arrows
214 J Ornithol (2016) 157:209–217
Fourth calendar year (4cy)
On average, 3.95 PP (SD = 1.10; range 3–7; n = 20) of
each wing were moulted, completing the first moult cycle
(Fig. 4). During their fourth calendar year, Bearded Vul-
tures moulted on average 7.05 SS (SD = 2.01; range 3–10;
n = 19) and 2.5 RR of each side of the tail (SD = 0.95,
range 1–4, n = 20). The moult of SS followed the trajec-
tory from the three above-mentioned foci, although two
more foci may appear in S10 and S13. These new foci are a
continuation of the moult wave. The same occurred in the
tail feathers, filling the gaps and starting again. The
moulting process during the 4th cy was less symmetrical in
PP (89.3 %) than in the previous calendar year, but mainl y
in SS (60.6 %) and RR (60.3 %).
Fifth calendar year (5cy)
The moult followed where they had left off in winter of the
previous year. Some birds (44.4 %) completed the second
moult cycle of all P during this year, and all birds had
advanced the second moult of SS, mainly in the three first
foci (S1, S5, S15). In contrast, 29.4 % of the birds still had
juvenile SS (mainly S10, S11, and S12) in summer, at the
middle of the moulting season. On average, 4.44 PP
(SD = 0.88; range 3–6; n = 9), 7.11 SS (SD = 1.17;
range 6–9; n = 9), and 3 RR (SD = 0.71; range 2–4;
n = 9) were moulted in the fifth cy. The symmetry of
moult in PP (82.29 %) and SS (58.65 %) was similar to 4
cy birds, but less in RR (40.09 %).
Moult in adults
Adults moulted almost half of the flight feathers every
year. On average, 4.8 PP (SD = 0.79; range 4–6; n = 22),
8.2 SS (SD = 1.4; range 5–10; n = 22), and 2.7 RR
(SD = 0.48; range 2–3 ; n = 22) were moulted in adults.
Moult did not follow an evident pattern at this age because,
from the third moult onwards, the perc entage of PP, SS and
RR moulted (and consequently the start point of each
moult) varied considerably among individuals and even
between wings of the same bird. In fact, the symmetry
between wings was on average 77.7 % in PP, 50.6 % in SS,
and 52.3 % in RR.
Bearded Vultures fledge between late June and early
August, and birds remain in their natal areas for the first
2 months after fledging, starting a post-fledging depen-
dence period close to the natal areas until the onset of
dispersal that coincides with the adult’s next breeding
season (Lo
pez et al. 2014). During the following
months, they will wander over extensive areas, and they
must learn to become self-sufficient, acquire flight skills,
find food resources, and exploit them efficientl y. This
period is, therefore, critical for survival (Margalida et al.
2013; Gil et al. 2014;Lo
pez et al. 2014). Possibly as
a consequence, we found that 2nd cy birds delayed start of
primary moult until late in May, and only few birds were
able to moult secondaries during the last month before the
end of the moulting season, in winter. During the second
calendar year, they only moulted on average four inner
primaries of each wing and rarely any secondaries. Possi-
bly, only birds that had enough energy or could start sooner
moulted the central pair of the tail feathers.
Feathers grown during the nestling period are of poorer
quality than those of grown-up birds (Ginn and Melville
2000), so the wear of the feathers may be more pronounced
until the individuals replace them. In the case of Bearded
Vultures, juvenile secondaries are significantly longer than
moulted ones, and these feather s show increasing degra-
dation from 2nd cy onwards, greatly contrasting with adult
feathers, which are of much better quality. During the
following years, birds should invest any surplus energy into
moult in order to improve plumage quality. Remaining
juvenile feathers are worn in the fourth calendar year.
Insofar as birds have moulted their plumage during their
first 4 cy, they will be in a better condition to overcome
winter. Subadults (3–5 cy) started moult in March, con-
siderably earlier than 2nd cy birds and adults, although
they showed high variability among individuals. As birds
gain experience they can mobilize more energy to moult
secondaries, increasing the percentage of secondaries
moulted with age, whereas the number of primaries
moulted per year remains the same or slightly increases
with age. We would expect that non-breeding birds moult
more feathers than breeders. The reduction in the number
of feathers moulted after breeding has been proposed to
reflect energy limitation due to reproductive activit y (Pi-
inen et al. 1984); however, we did not have data on
breeding status. In the case of subadults, foraging inexpe-
rience may be a limiting factor for the extent of moult.
The moult pattern of Bearded Vultures is char acterised
by the replacement of few flight feathers during the first
moult periods. Following the usual moult pattern in large
soaring raptors (i.e. moult waves; Edelstam 1984 ; Clar k
2004), the innermost primaries and neighbouring secon-
daries tend to be replaced more often than others (Houston
1975; Mundy 1982; Snyder et al. 1987; Pyle 2005;
Zuberogoitia et al. 2013a). In fact, our results (Fig. 4)
showed that before outer primaries or some secondaries of
the fourth and fifth foci (S10 and S13) were moulted for the
first time, bir ds had replaced inner primaries and secon-
daries for the second time. Langst on and Rohwer (1995)
J Ornithol (2016) 157:209–217 215
suggested that Laysan (Phoebastria immutabilis) and
Black-footed Albatrosses (Pygathrix nigripes) more often
replace those primaries that drag on the sand of the atolls
where the birds breed and become severely abraded. In the
same line, Brommer et al. (2003) showed that Ural Owls
(Strix uralensis) more often replace oute r primaries, sug-
gesting that the allocation of position-specific energetic
costs may benefit large birds. The moult pattern of subadult
Bearded Vultures reflects the importance of the good
maintenance of inner primaries and secon daries for soaring
and gliding.
Bearded Vultures reach definitive plumage in their 6th
calendar year (Sese
2011), approximately the same age at
which they start to establish a territory (Lo
pez et al.
2014). This, in turn, reflects the importance of the rela-
tionship between the acquisition of definitive plumage, the
reach of sexual maturity and the settlement in a breeding
territory (Rohwer et al. 2011).
Adults started moult 1.5 months later than subadults,
possibly due to breeding requirements. The onset of moult
synchronizes with the presence of 1-month-old nestlings
(see Margalida et al. 2005). For example, Rohwer et al.
(2011) showed that the Black-footed Albatross’s moult is
so time-constrained by reproduction that some individuals
fail to replace all their flight feathers every 2 years. This
resulted in reduced breeding performance due to skipping
behaviour or breeding with worn feathers. Moult in birds
that overlap moult and breeding was found to be slow and
protracted (Foster 1975; Rohwer et al. 2009 ), confirming
the high cost of replaci ng flight feathers while breeding.
Most adults moulted all flight feathers in 2 year s. They
started a bit later than subadults, moulted more feathers,
but duration was almost the same. Our findings correspond
to those of Dietz et al. (2013) who showed that moult of
adult Red Knots (Calidris canutus) is seriously time-con-
strained by reproduction and that adults moult later but
faster than second calendar year birds.
Adult Bearded Vultures show a high degree of asym-
metry, mainly in secondaries and tail feathers. According
to Rohwer et al. (2011) and Zuberogoitia et al. (2013a)
some mechanism may enable them to replace feathers that
are damaged or unusually worn, regardless of the biennial
cycle. However, asymmetry appears to have negative
consequences for survival (Brommer et al. 2003). In
agreement with Brommer et al. (2003), asymmetry in pri-
maries, which are used for flight propulsion (Hickman et al.
1993), appears to be less than the asymmetry in secon-
daries, which are used for lift.
Acknowledgments This paper has been developed under the
agreement signed by the Foundation for the Conservation of the
Bearded Vulture (FCQ), Arago
n regional government and the Spanish
Ministry of Environment, under the actions of the Bearded Vulture
Recovery Plan in Arago
n and the Bearded Vulture Reintroduction
Program in Picos de Europa. We are indebted to the Departamento de
Agricultura, Ganaderı
a y Medio Ambiente (Arago
n regional gov-
ernment), European Union (LIFE 1998–2006, and INTERREG IIIA
2002–2006 programs), MIMAM (Spain), Guardia Civil (GREIM),
n Forest Rangers (APN), Wildlife Rehabilitation Centre at La
Alfranca (Zaragoza), LVFS, IREC-CSIC, EBD-CSIC, SEO/BirdLife,
n’ Ringing Group, Trango, Zeiss and Land Rover. Thanks to J
Guiral, J Insausti and M. Alcantara. G. Gonza
lez, I. Otra, J. Serra, J.
nchez, J. Marti, S. Marcedos, J. Vecino, D. Forsman, for sharing
with us their picture collections of Bearded Vultures. L Palomares
helped us drawing the Fig. 4. Special thanks are due to all the
members of the FCQ and particularly to O
ez, G Baguena, L
Lorente, R Antor, G Che
liz, JC Ascaso and JC Gonzalez. Two
anonymous reviewers provided helpful comments on the manuscript.
This paper complies with the current laws in Spain. The authors
declare that no conflict of interest exists.
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... Adult falcons (Falconidae) typically moult their flight feathers in one moult cycle (Pyle 2005;Zuberogoitia et al. 2018), but the timing and extent of juvenile flight feather moult varies among species (Zuberogoitia et al. 2016). Juvenile falcons have distinct juvenile plumages, differing from adults in terms of colour and pattern, and with sexual differences in plumage among several species (Brown and Amadon 1968). ...
... Juvenile falcons have distinct juvenile plumages, differing from adults in terms of colour and pattern, and with sexual differences in plumage among several species (Brown and Amadon 1968). Post-juvenile body moult (preformative moult) is staggered between 6 and 12 months after fledging (Zuberogoitia et al. 2016). As a result, the timing and extent of post-juvenile moult determines the appearance of the individual, influencing its attractiveness, social status and camouflage (Kiat et al. 2019). ...
... The extent of post-juvenile moult advanced more in females than males in response to historical climate warming trends (Kiat et al. 2019), suggesting that moult in juvenile females may be more sensitive to environmental variation (Delhey et al. 2020). There are often age-related differences in the extent and timing of moult (Zuberogoitia et al. 2016). Juveniles require more energy to obtain the same food intake as adults and are not constrained by breeding activities, and thus normally start moulting later than adults. ...
... Adult falcons (Falconidae) typically moult their flight feathers in one moult cycle (Pyle 2005;Zuberogoitia et al. 2018), but the timing and extent of juvenile flight feather moult varies among species (Zuberogoitia et al. 2016). Juvenile falcons have distinct juvenile plumages, differing from adults in terms of colour and pattern, and with sexual differences in plumage among several species (Brown and Amadon 1968). ...
... Juvenile falcons have distinct juvenile plumages, differing from adults in terms of colour and pattern, and with sexual differences in plumage among several species (Brown and Amadon 1968). Post-juvenile body moult (preformative moult) is staggered between 6 and 12 months after fledging (Zuberogoitia et al. 2016). As a result, the timing and extent of post-juvenile moult determines the appearance of the individual, influencing its attractiveness, social status and camouflage (Kiat et al. 2019). ...
... The extent of post-juvenile moult advanced more in females than males in response to historical climate warming trends (Kiat et al. 2019), suggesting that moult in juvenile females may be more sensitive to environmental variation (Delhey et al. 2020). There are often age-related differences in the extent and timing of moult (Zuberogoitia et al. 2016). Juveniles require more energy to obtain the same food intake as adults and are not constrained by breeding activities, and thus normally start moulting later than adults. ...
Full-text available
Amur Falcons Falco amurensis undergo one of the most extreme migrations of any raptor, crossing the Indian Ocean between their Asian breeding grounds and non-breeding areas in southern Africa. Adults are thought to replace all their flight feathers on the wintering grounds, but juveniles only replace some tail feathers before migrating. We compare the extent and symmetry of flight feather moult in a large sample of Amur Falcons killed at communal roosts during two hailstorms in KwaZulu-Natal, South Africa in March 2019, shortly before their northward migration. Most adults had completed replacing their remiges, with only a few still growing 1–3 feathers (mainly secondaries), but most were still growing their tail feathers. Juveniles only replaced tail feathers. Moult typically was distal from the central rectrices, but 25% of adults and 1% of juveniles replaced the outer tail first, and a few individuals exhibited other moult patterns (simultaneous moult across the tail, or among the inner and outer feathers). These different moult strategies were independent of sex. Adults that replaced the outer tail first typically had replaced a greater proportion of the rectrices (mean ± SD; 0.81 ± 0.19) than adults starting from the central tail (0.17 ± 0.08). Proportionally fewer distal moulting adults were killed on 9 March than 21 March, resulting in the average proportion of rectrices replaced by adults decreasing between the two storm events from 0.52 ± 0.26 to 0.43 ± 0.23. By comparison, juvenile tail moult increased from 9 March (0.34 ± 0.18) to 21 March (0.40 ± 0.15). Overall, the probability of replacement for T1 was similar for adults (0.82) and juveniles (0.83), but adults were more likely to have replaced T2–6 (0.40–0.45) than juveniles (0.18 for T2 and 0.04–0.07 for T3–6). Asymmetry in tail moult was greater at T1 for adults (15%) than juveniles (10%), but asymmetry for T2 to T6 was greater in juveniles (3–10%) than adults (1–4%), especially given the greater probability of feather replacement in adults. Despite these differences, the degree of asymmetry was less than expected by random replacement across all rectrices in both age classes. Interestingly, moult tended to be more advanced on the left than right side of the tail. The extent of tail moult was correlated with body condition in adults and juveniles, suggesting that moult pattern might be used as an indicator of fitness in falcons.
... However, two birds were growing secondaries distally at S3 and S25, whereas one was growing secondaries proximally at S27 of primaries replaced each year. However, the resultant age contrasts between adjacent moult waves were generally minor and may have resulted from withinseason age differences rather than across season differences, so it was not feasible to assess the proportion of feathers replaced in each moult (Zuberogoitia et al. 2016). We were able to recognise nodal points in the secondaries where there was a new feather older than adjacent new feathers (cf. ...
... We modelled the moult of Cape Gannets using the data type 1, requiring only data on whether a bird has not yet started moult, is in moult, or has completed moult, using only the current year's moulting feathers for analyses (cf. Zuberogoitia et al. 2013Zuberogoitia et al. , 2016Zuberogoitia et al. , 2018. We fitted the model using the maximum likelihood method (Underhill and Zucchini 1988;Newton 2009) and calculated 95% confidence limits for moult parameters following Erni et al. (2013). ...
Full-text available
Little has been reported on moult in sulids, including gannets. The Cape Gannet Morus capensis is an endangered seabird endemic to southern Africa. We describe the timing, duration, symmetry and sequence of flight feather moult in Cape Gannets from two breeding colonies and assess whether moult can be used as an index of condition. Using the Underhill-Zucchini model, we estimate moult parameters based on the proportion of feather mass grown. Adult Cape Gannets began primary moult at the beginning of January (2–3 January ± 28 days SD) at both colonies. Primary moult is protracted, with multiple active centres (mean ± SD 1.8 ± 0.8, range 1–4) and 2.0 ± 0.9 feathers growing at the same time (range 1–5). Primary moult is suspended by early June at Malgas Island (estimated duration of moult ± SE, 153.9 ± 4.1 days) and late June at Lambert’s Bay (176.5 ± 5.5 days). Secondary moult commenced in late January and proceeded from two nodal points. Despite more secondaries (3.3 ± 1.9, range 1–8) being grown simultaneously than primaries, 8% of birds were still moulting secondaries at the start of the breeding season. However, it was not certain that these individuals were breeding. Tail moult also overlapped with that of the primaries, with multiple active centres (2.7 ± 1.2, 1–6) and 2.9 ± 1.3 feathers growing at the same time (range 1–8). Almost all primary (98%) and secondary moult (97%) was symmetrical, but there was little symmetry in tail moult (54%). Rectrix symmetry tended to be greater among gannets at Malgas Island (T1: 58%; T2–T6: 67–73%) than at Lambert’s Bay (T1: 50%; T2–T6: 55–66%). Differences in moult duration and perhaps asymmetry between locations may be linked to foraging conditions, given that Lambert’s Bay gannets are thought to be under greater food stress than Malgas birds.
... The latter two tend to correlate negatively with some parameters of the definitive molt phenotype, including number of barbs and feather density . Duration of remex replacement vary from three to four weeks in some synchronous molting species to several annual cycles in some large raptors, although most small to medium-size species of the Holarctic spend 8-12 weeks , Zuberogoitia et al. 2016. Duration of molt in Neotropical species is longer probably because of their slower pace of life (Wiersma et al. 2007). ...
... On the other hand, most large species cannot renew their whole plumage within a year and molt must be protracted along multiple annual cycles (Zuberogoitia et al. 2018, Jenni & Winkler 2020a. Other molt elements also vary among episodes within the individual, including intensity (Zuberogoitia et al. 2016) and plumage quality (Weber et al. 2010). ...
Molt is the process of plumage renewal by which birds maintain and adjust its functionality throughout their lifecycle. Multiple elements have been tackled in bird molt research (timing, duration, sequence, intensity, extent, feather growth rate, and plumage quality), but major gaps still exist on molt regulation, and especially on molt evolution. This thesis focuses on one molt element extensively recorded since mid-20th century but seldom studied as an individual trait: the set of feathers replaced after a given molt episode by one individual (here referred to as final molt phenotype). This is surprising because feathers differ in their function (e.g. signaling, thermoregulation, contribution to different flight functions, durability), costs of production, and morphology (e.g. exposure, mass, shape), all of which can be targeted by natural selection. Therefore, the final molt phenotype should be under strong selective pressures, suggesting that its regulation has been shaped during evolution to optimize plumage performance throughout the bird’s lifecycle. This thesis explores the potential of analyzing final molt phenotypes as is (instead of being analyzed partially or indirectly) to uncover underlying mechanisms of molt regulation and to provide insights on the evolution of molt in passerine birds. Following are the main findings presented in this thesis. Final molt phenotypes differed between the post-juvenile and the pre-breeding molts along the passerine phylogeny. A nested organization of final molt phenotypes suggested a rank of feather molt importance as underlying rule of molt. However, deviations from perfect nestedness were largely associated with the pre-breeding molt. Shared ancestry explained a large portion of final molt phenotype variation, likely due to constraints associated to plumage morphology, which is highly conserved in passerines. Phylogenetic analyses confirmed the phylogenetic independence of the pre-breeding molt and the strong phylogenetic signal of the post-juvenile molt. Further, they showed the overlooked relevance of environmental factors on the evolution of passerine molt, although their effect varied among taxonomic groups and molt episodes, thus highlighting the flexibility and adaptiveness of molt. Findings exposed in this thesis confirm the relevance of the final molt phenotype as a promising element to advance in our understanding of bird molt.
... However, some mediumsized accipitrids need more than one year in order to complete one moult cycle, while large raptors need several years (from 2 to 4 years; Snyder et al. 1987;Zuberogoitia et al. 2013c). In some species the immature plumage is changed first for a subadult plumage and later for an adult dress (Watson 2010;Zuberogoitia et al. 2016). ...
... Bearded vultures reach definitive plumage in their 6th calendar year (Sesé 2011;Zuberogoitia et al. 2016), approximately at the same age at which they start to establish a territory . This, in turn, reflects the importance of the relationship between the acquisition of definitive plumage, the reach of sexual maturity and the settlement in a breeding territory (Rohwer et al. 2011). ...
Full-text available
Raptors are limited by suitable breeding habitat, and they have specific nest-site requirements. Habitats of high quality presumably have the resources required to sustain relatively high rates of survival and reproduction. High-quality individuals would occupy territories of higher quality and would have greater fitness. Many birds may use their own reproductive success to assess the quality of their territories, and breeding failure would act as a determinant for dispersal, increasing an individual’s propensity to move to a better habitat. Food supply, nest-site availability, weather conditions and bird experience seem to act through the body condition of the female and are known to limit raptor populations. Quality of nesting territories and breeding success vary widely with different factors.
... Aunque con un pequeño desfase, la historia del estudio de la muda en España se ajusta al cronograma general esbozado arriba, donde el grueso de las contribuciones científicas se centran en descripciones de fenología, secuencia y extensión de la muda, y su aplicación potencial a la determinación de la edad de las aves (véase la ingente labor de Javier Blasco-Zumeta, En este sentido, se ha realizado una contribución muy significativa en lo que se refiere a especies de aves de distribución mediterránea [250][251][252] , (cuasi) endemismos ibéricos [253,254] y macaronésicos [255][256][257] , así como en aves rapaces [258][259][260][261][262] . Últimamente, además, se vienen desarrollando también trabajos de carácter más metodológico para describir procesos de muda poco habituales, como la muda suspendida en el caso del piquituerto común [263] . ...
... Between these two strategies, there are intermediate moult patterns that are often characterised by complete moults in adults, and partial ones in first-year birds (Svensson 1992). In the largest species, like many eagles and vultures and some owls, feathers cannot all be replaced in a single year, giving rise to more complex moult patterns that, overall, often allow several age classes to be differentiated (Baker 1993, Demongin 2013, Zuberogoitia et al 2015. ...
Determining the age of specimens is of great help in wildlife management, especially for rare or threatened species in which each individual has a high value. In birds, differences in moulting pattern between juveniles and adults may in some cases allow determination of a bird’s age from the examination of its plumage. In the present study, we analyse the moult of 19 breeding individuals of White-backed Woodpecker Dendrocopos leucotos lilfordi captured for GPS tagging in the Pyrenees, in order to describe, for the first time, the moulting pattern of this endangered woodpecker. Two well-differentiated groups of adult birds were identified: those that underwent a partial moult, and were classified as second-calendar-year birds, and those that performed a complete one and were classified as older. The first group had renewed most lesser and median coverts, all primaries and the innermost greater coverts, thus showing clear moult limits between the primaries and secondaries and within the greater coverts. Some individuals also replaced up to two more greater coverts (GC5–6). Individuals classified as older birds showed all feathers to be of a single generation, indicating that they had undergone a complete moult. A few individuals in this category retained a few unmoulted secondaries and primary coverts, however. A recapture of a bird with a complete moult, which had been captured a year before showing a partial moult, would confirm these moult sequences to be age dependent. This moulting pattern is very similar to that described for other spotted woodpeckers, and allows researchers to determine the ages of breeding individuals during the nesting season.
... We used high-quality photos taken in the field from which moult patterns can be inferred (Snyder et al. 1987;Zuberogoitia et al. 2016;Vieira et al. 2017). Digital cameras (i.e. ...
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Abstract Background Most of long-distance migratory raptors suspend moult during migration but detailed information is patchy for most of the Palearctic species. The aim of this research is to verify if active moulting in migrating Western Marsh Harriers occurs and to quantify the extent of moulting along the season focusing on primary feathers. Methods During a whole post-breeding migration at the Strait of Messina in Southern Italy, we gathered information about symmetrical flight feather moult from 221 adults by taking pictures of raptors passing at close range. Results We found active moulting primaries during autumn migration in 48.4% of our samples. Slight differences on the extension and timing among sex classes were recorded during the season, with adult females showing a more advanced moult stage than adult males. Conclusion The finding that the extension of the suspended moult was already defined in migratory individuals might be explained as an adaptation to minimize the energy required for moulting during migration.
Moult is a process, usually occurring annually, in which birds replace their plumage. It is one of the most crucial life-history traits because it restores the functions of plumage and allows a bird to adapt to environmental conditions or special seasonal needs such as breeding and camouflage during non-breeding season. Consequently, moulting has advantages in terms of future performance. However, it also has immediate costs related to producing protein-rich tissue, reduced thermoregulation and flight performance. Expression of such costs may depend on a wide array of physiological and environmental factors experienced by an individual. Considering a variety of factors affecting moult dynamics in single studies, we use a systematic meta-analytical approach to summarise existing evidence and look for general patterns in how moult depends on both extrinsic (environment, ecological variability) and intrinsic (physiology, energy reserves, life stage) factors.
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The Oriental Honey-buzzard Pernis ptilorhyncus, which breeds in the areas of southern Siberia, northern Mongolia, northeastern China, Korea and Japan, and that migrates south for winter is a suitable and attractive subject for studying the behavioural and evolutionary ecology of bird migration. In this study, we investigated the morphological diversity, sex, and age-related characteristics of the Oriental Honey-buzzard populations using photographic analysis methods as they pass by Socheong island in autumn from 2014 to 2016. According to the study of analyzing 1,366 individual birds, 15.37% of the birds were more than 2 years old and 83.6% of the birds were juveniles. The sex ratio was 11.79% for males and 3.58% for females. Males were three times more than females. At the time zone of migration, females adult and juveniles migrated at 10 to 11 and 13 to 16 o'clock while male adults continued to move 10 to 16 o'clock. In the analysis of populations, there was a statistically significant difference between females, males and females(two-way ANOVA test, F=32.266, df=2, p<0.05). The morphological diversity analysis showed that 39.13% of red-brown morphs and 36.02% of intermediate morphs were males. And females were 48.98% reddish brown and 20.14% middle females. However, in the case of juvenile, the morphological diversity ratio of the feathers was not statistically significant,
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Examination of 1622 specimens indicates that North American Falconiformes show a wide variety of remigial (primary and secondary) replacement strategies, detectable throughout the year by evaluation of replacement patterns in the wings. Most Falconidae undergo complete prebasic molts whereas most Accipitridae display retained secondaries or show stepwise molt replacement patterns (“Staffelmäuser”). Among individuals exhibiting Staffelmäuser, minimum age can be inferred up to 5 years (fifth-basic plumage) by the number of “replacement waves” present among the primaries. It may also be able to infer breeding status during the previous summer by “suspension limits,” resulting from the interruption of molt during breeding. Among Accipitridae, Staffelmäuser occurred in species with greater mass, higher wing loading, longer migration distance, and more open rather than wooded foraging habitats: species that experience time constraints on molting and incur greater costs from large gaps in the wing. Thus, this study supports both the “time-constraints hypothesis,” suggesting that Staffelmäuser is a consequence of insufficient time for a complete annual molt, and the “aerodynamic hypothesis,” suggesting that Staffelmäuser reflects an adaptive need to replace as many feathers as possible without inhibiting flight efficiency. Time constraints may have been a proximate cause of Staffelmäuser among Falconiformes, with improvements to flying efficiency being an ultimate adaptive benefit.
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The regression methods frequently used to estimate the parameters associated with primary moult in birds are unsatisfactory. Results obtained using least squares regression, and various ad hoc adaptations, are so obviously incorrect that many authors have fitted lines ‘by eye’ (Newton 1968, Thomas & Dartnall 1971, Elliott et al. 1976, Morrison 1976, Appleton & Minton 1978). In a comparison of seven regression methods, estimates of the average starting date varied between 29 June and 31 July, completion date between 2 and 24 October, and duration of moult between 72 and 109 days for the Redshank Tringo totonus, in spite of the very large sample of 1482 observations (Summers et al. 1983). In this paper we present a new approach to the analysis of primary moult and develop a mathematical model specifically designed for moult data.
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In a seasonally fluctuating environment migratory birds face decisions relating to how to schedule their main life-history activities, i.e. breeding, moult and migration. The time required to complete any one of these depends on overall size. In this paper I derive scaling functions about how time required for breeding, moult and migration depends on body mass. The sum of these increases with increasing body mass with a critical mass where the duration of non-overlapping breeding, moult and migration is equal to one year. Beyond this mass one or more of the processes must be modified. Large species may refrain from annual breeding and skip years without breeding. The replacement of one set of feathers may also take more than one year, or in long-distance migrants the timing of moult is shifted from a post-breeding moult before autumn migration to a post-migration moult in the wintering area. Different adaptations for efficient migration are also discussed. Finally, I use a simple graphical model to derive a condition for when overloading fuel at the final stopover site is worthwhile, leading to arrival at the breeding site with surplus energy that may be used as capital for breeding.
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Females did not start moulting their wing feathers until in the late nestling period or early fledgling period. No males were in active moult during the nestling period. The high number of moulted outer primaries in the first and subsequent moults may be adaptive because of the wear of the sound muffling combs on the leading edges of the outer primaries. There was a decreasing trend in the number of moulted primaries and secondaries in the first 6 moults. The number of moulted flight feathers decreased from the birds having failed their breeding attempt to those having 1, 2, 3 or 4-5 young. This was explained by the energetic strain of the presumably long fledgling period. Ural owls moulted more of their flight feathers in those years when only few females laid eggs compared to those years when almost all females laid.-from Authors
The wings and tail of most postjuvenile large birds of prey present a blend of very differently worn quills. By carefully recording the state of wear and fading of every quill in a large number of specimens, whether actively moulting or not, it is possible to reconstruct the details of the underlying moult process. The pattern is serially continuous, with several moult waves proceeding simultaneously but slowly through 7 separate moult units in each wing, including the bastard wing; and somewhat irregularly alternating within 2 moult units in each half of the tail.-from Author
Laysan and Black-footed Albatrosses show a bidirectional pattern of incomplete molt in their primaries which has never before been described for any bird. Juveniles molting their flight feathers for the first time replace only their distal three or four primaries. In older birds the ten primaries are divided at their mid-point into two series, each with an independent set of rules for replacement. Unlike most other birds, the primaries of the two series are replaced in opposite directions, with molt proceeding toward the wing tip in the outer series and toward the body in the inner series. The outermost feathers of the distal series are replaced every year without fail; the time available to molt determines how many feathers of this series are replaced. In the inner series, feather replacement occurs only every second to third year. When molt does occur in the inner series it is normally incomplete, and it proceeds in a wraparound pattern which assures that the oldest and most worn feathers are always the first to be replaced.
Primary molt of the California Condor (Gymnogyps californianus) was studied intensively from 1982 through 1985, using repeated flight photographs of the remaining individuals in the wild population as a basis for most analyses. On the average, wild condors replaced 4.4 of the 8 emarginated primaries on each wing each year. The specific primaries molted were generally the ones missed in the previous year and were usually well-distributed among the eight possibilities, with a tendency for low-numbered primaries to molt earlier than high-numbered primaries. Within individuals, molt of one wing was commonly very different from that of the other wing. Primary molt of captive juveniles was similar to that of wild juveniles. The interval from loss to full replacement of individual primary feathers was normally 3½ to 4 months, with the primaries closest to the leading edge of the wing growing most slowly. Most primaries were shed between 1 February and 1 September. Primaries lost in late fall and early winter were not replaced until the following summer, indicating interrupted molt over the winter. In general, primary molt of the condor differs from that of smaller cathartids in being highly seasonal, highly variable in sequence, highly asymmetric between wings, and in following a roughly 2-year cycle. Molt of the condor shows many similarities to that of the White Stork (Ciconia ciconia) and to that of large accipitrid vultures.