ArticlePDF Available

Abstract and Figures

Moult is one of the three main energy‐demanding events in the yearly cycles of birds, and in most species occurs at a different time from breeding and migration. The sequence in which these events occur varies according to the ecological circumstances in which particular populations live, and in general moult is more variable in timing than other events. Some migratory birds moult in their breeding areas after nesting is over; others moult at a staging area on migration; while others moult in winter quarters. Yet others show a split moult, replacing part of their plumage in one place and part in another, moult being arrested during the intervening migration. Different variants in these patterns occur in different populations of the same species. Some types of birds overlap breeding and moult, and some also overlap moult and migration, especially body moult which can occur without reducing flight efficiency. Most of our knowledge of moult is based on museum skins and, now that appropriate statistical models are available to analyse it, moult is increasingly being studied in free‐living birds, the main parameters of ecological interest being its timing and duration. Recent models for analysing moult data, and some of the pitfalls, are discussed briefly in this paper. More field study of moult is needed, particularly because of its relevance to annual cycle and population processes, and hence to its potential application in conservation‐based research. Ringers are the only people at present able to fill this gap in knowledge.
Content may be subject to copyright.
© 2009 British Trust for Ornithology
Ringing & Migration (2009) 24, 220–226
Moult and plumage
Centre for Ecology and Hydrology, MacLean Building, Benson Lane, Crowmarsh Gifford,
Wallingford, Oxfordshire OX10 8BB
Moult is one of the three main energy-demanding events in the yearly cycles of birds, and in most species
occurs at a different time from breeding and migration. The sequence in which these events occur varies
according to the ecological circumstances in which particular populations live, and in general moult is more
variable in timing than other events. Some migratory birds moult in their breeding areas after nesting is
over; others moult at a staging area on migration; while others moult in winter quarters. Yet others show a
split moult, replacing part of their plumage in one place and part in another, moult being arrested during
the intervening migration. Different variants in these patterns occur in different populations of the same
species. Some types of birds overlap breeding and moult, and some also overlap moult and migration,
especially body moult which can occur without reducing flight efficiency. Most of our knowledge of moult
is based on museum skins and, now that appropriate statistical models are available to analyse it, moult is
increasingly being studied in free-living birds, the main parameters of ecological interest being its timing
and duration. Recent models for analysing moult data, and some of the pitfalls, are discussed briefly in
this paper. More field study of moult is needed, particularly because of its relevance to annual cycle and
population processes, and hence to its potential application in conservation-based research. Ringers are
the only people at present able to fill this gap in knowledge.
* Email:
My aim in this paper is to describe how moult (the period
of plumage renewal) fits within the annual calendar of
different bird species, how it can be studied during ringing
operations, and analysed using appropriate statistical
methodology to estimate its timing and duration. Although
moult is one of the three major events in the annual cycles
of birds, it has been much less studied than breeding and
migration (for reviews see Stresemann & Stresemann 1966,
Jenni & Winkler 1994, Kjellén 1994, Newton 2008). This
is partly because of a general lack of appreciation of its
relevance to the annual cycle and population processes,
and its potential role in conservation-driven research.
Feathers are special lightweight structures consisting of
a tough, inert protein called keratin. They form one of
the defining features of birds, whether the soft insulating
feathers that cover the body surface or the stiffer flight
and tail feathers that provide the aerofoils which permit
flight. Once they are formed, feathers become attached
dead structures in which damaged parts cannot be repaired.
They deteriorate mainly through the action of physical
wear, sunlight and feather mites, and must therefore be
renewed periodically. During a moult, feathers are generally
replaced sequentially, in predetermined order, so that
body insulation and (in most birds) flight are maintained
throughout. Each feather is shed as a new one begins to
grow below, and each has a characteristic growth curve,
taking its own set period to reach full length. Within
species, equivalent feathers in different individuals take
about the same time to grow, so that individual variation
in moult duration is due much more to variations in the
intervals between the shedding of successive feathers than
to variation in the growth rates of their replacements (eg
Newton 1967, 1969, Serra 2000). Many birds moult only
once a year, others two or more times. Moults may be
complete, involving body, wing and tail feathers, or partial,
involving body feathers alone (and sometimes a few flight
The processes of breeding, moult and migration all require
extra food above the needs of daily maintenance and in
many birds occur mainly at different seasons. Moult cannot,
therefore, be considered in isolation from other events in
the annual cycle, and to a large extent the three main events
should be viewed as an integrated whole. In addition, many
birds show a quiescent period in winter, during which
they are not breeding, moulting or migrating. Outwardly,
they seem to be doing little except eating and surviving,
but inwardly they may be undergoing some physiological
change, such as growing gonads in preparation for breeding
at a later date. Not all species show this quiescent stage,
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
Moult and plumage 221
Figure 1. Eight common sequences of annual cycle events described
among European migratory birds. The term ‘quiescence’ denotes a
period when the bird is not breeding, moulting or migrating.
Pre-breeding migration breeding moult post-breeding
migration. Examples: Chaffinch Fringilla coelebs, Common
Redpoll Carduelis flammea, Thrush Nightingale Luscinia luscinia,
Fieldfare Turdus pilaris, Jack Snipe Lymnocryptes minimus.
Pre-breeding migration breeding post-breeding migration
part 1 moult post-breeding migration part 2. Examples:
Great Reed Warbler Acrocephalus arundinaceus, River Warbler
Locustella fluviatilis, Northern Lapwing Vanellus vanellus, some
populations of Green Sandpiper Tringa ochropus.
Pre-breeding migration – breeding – post-breeding migration
moult. Examples: Common Rosefinch Carpodacus erythrinus,
Barn Swallow Hirundo rustica, Common Swift Apus apus,
Whimbrel Numenius phaeopus, Harlequin Duck Histrionicus
histrionicus, together with some shearwaters, terns and skuas
that breed and winter in opposite hemispheres. In some
of these species, the moult is prolonged and the quiescent
period short or non-existent (as in Barn Swallows wintering
in South Africa).
Pre-breeding migration breeding moult part 1 post-breeding
migration moult part 2. Examples: Barred Warbler Sylvia
nisoria, Alpine Swift Apus melba, Scops Owl Otus scops,
however, as some pass without obvious break from one
major process to another (Newton 2008).
At least eight different sequences of events occur
commonly among different European bird populations
and others less commonly, depending on the particular
ecological circumstances in which each population lives
(Fig 1). In general, residents and short-distance migrants
moult in summer after breeding (residents more slowly: Fig
1, sequence 1). Long-distance migrants moult either in late
summer in the breeding area (as in sequence 1), in autumn
migration, phase 2
migration, phase 1
phase 1
phase 2
migration, phase 1
migration, phase 2
phase 1
Moult, phase 2
migration and
migration, phase 1
Moult, phase 1
Moult, phase 2
migration, phase 2
migration and moult
at a migratory staging area (sequence 2) or in winter quarters
(sequence 3) (Bensch et al 1991, Jenni & Winkler 1994,
Newton 2008). Moulting in wintering areas is widespread
among northern-hemisphere species which spend their
non-breeding period in the southern hemisphere, where
the seasons are reversed (the southern summer coinciding
with the northern winter). Less constrained by time, they
also spread the moult over a longer period.
In many other migratory species, the moult occurs partly
in one area and partly in another, separated by migration.
Bee-eater Merops apiaster, Red-necked Nightjar Caprimulgus
ruficollis, Collared Pratincole Glareola pratincola, Marsh
Sandpiper Tringa stagnatilis, juveniles of Common Quail
Coturnix coturnix.
Pre-breeding migration breeding moult part 1 post-breeding
migration part 1 – moult part 2 – post-breeding migration part
2. Examples: Kentish Plover Charadrius alexandrinus, Spotted
Redshank Tringa erythropus, some individuals of Curlew
Sandpiper Calidris ferruginea.
Pre-breeding migration breeding post-breeding migration
part 1 – moult part 1 – post-breeding migration part 2 – moult
part 2. Examples: Wilson’s Phalarope Phalaropus tricolor,
Spotted Sandpiper Actitis macularia, and other populations of
Pre-breeding migration breeding first (post-nuptial) moult
post-breeding migration second (pre-nuptial) moult. Example
with two complete moults per year: Willow Warbler Phylloscopus
trochilus; examples with one complete and one partial moult
per year: Melodious Warbler Hippolais polyglotta and many
Pre-breeding migration breeding post-breeding migration
– post-nuptial moult – pre-nuptial moult. Examples: Lanceolated
Warbler Locustella lanceolata and some other Locustella
warblers, Curlew Sandpiper Calidris ferruginea.
222 I. Newton
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
The moult can be split between the breeding area and
wintering area (sequence 4), between the breeding area
and a staging area (sequence 5), or between a staging and
wintering area (sequence 6). The moult normally stops
during migration, so that the bird can fly with a full set
of flight feathers, some new and others old. The bird
resumes the second part of moult wherever it left off in
the first part (with few exceptions). In the last two of these
patterns (sequences 5 and 6), a split moult is associated
with a split migration. In other (mostly large) species,
split moults are associated with breeding (as moult stops
temporarily during chick feeding), or with periods of winter
food shortage. Comparing these various patterns among
species, moult is much more variable in timing than is
breeding or migration, probably because moult scheduling
is less crucial.
The story does not end here, for while some migratory
species have a single split moult, replacing their feathers
once but in two bouts, other species have two separate
moults, replacing the same feathers twice in one year. One
moult occurs either before or after autumn migration (the
post-nuptial moult), and the other before and during spring
migration (the pre-nuptial moult) (sequences 7 and 8). In
most twice-yearly moulting species, the autumn moult is
complete and the spring moult is partial, involving body
feathers only (and sometimes a few tertial, secondary or
tail feathers). However, in a small proportion of species
that moult twice each year, such as the Willow Warbler
Phylloscopus trochilus, both moults are complete, involving
the replacement of both body and wing feathers. In some
species with two moults per year, both plumages look the
same (as in Willow Warbler), but in other species pre-
nuptial moult gives rise to a special breeding plumage,
more brightly coloured than the drab winter garb. Some
species, such as the Linnet Carduelis cannabina and
Brambling Fringilla montifringilla, acquire their breeding
plumage, not by a pre-nuptial moult, but by abrasion, in
which dull feather tips wear off to expose colour below. Pre-
nuptial moults of the body feathers occur in many species
of waders, and usually overlap with spring migration. In
diving and dabbling ducks, the pre-nuptial moult (mainly
body feathers) follows a few weeks after the post-nuptial
moult (complete). In consequence, drakes are in dull
‘eclipse’ plumage (equivalent to winter plumage) for only
a few weeks each year and in bright breeding plumage for
most of the year (Cramp & Simmons 1977, Bluhm 1988).
In association with this, many species of ducks form pairs
while in winter quarters, whereas most other birds pair up
in breeding areas.
These various generalisations apply mainly to small or
medium-sized birds, in which moult occurs as a distinct
event in the annual cycle, typically lasting two to three
months (Fig 1). In many species, moult, breeding and
migration each occupy short enough periods that they can
all be fitted within a year without overlap, and often with a
quiescent period as well. In some large birds, however, such
as vultures and albatrosses, breeding cycles and moult take
so long that they cannot both be fitted within a calendar
year without overlapping, and in some such species moult
may also overlap with migration, especially body moult
which does not reduce flight efficiency (Stresemann &
Stresemann 1966).
In most raptors, moult begins during incubation (earlier
in females than males) and overlaps with most of the
breeding cycle, although it may be arrested during chick
rearing (as in the Sparrowhawk Accipiter nisus, Newton
& Marquiss 1982). Smaller raptor species can normally
finish their moult before the post-breeding migration,
but larger ones, which take longer to grow their feathers,
arrest moult during migration, and continue after reaching
winter quarters (as in the Osprey Pandion haliaetus and
Honey Buzzard Pernis apivorus). In some of the largest flying
birds, such as vultures, condors, storks and albatrosses,
each moult cycle lasts more than a year, but again may
be interrupted during difficult periods, such as chick-
rearing. Otherwise such birds appear to moult more or less
continuously, and may have two or more moult waves in
the primary and secondary flight feathers at once (so-called
serial moult). In addition, some large aquatic birds, such
as waterfowl and grebes, circumvent the problem of slow
feather growth in a different way, by moulting all their flight
feathers simultaneously (becoming temporarily flightless).
The whole feather series is then replaced within the time
taken to grow the longest primary (about four weeks in
ducks, six weeks in geese).
Birds clearly show great variation between species in the
sequence of events through the year, their duration and
extent of overlap. Moreover, unlike a successful breeding
attempt, moult and migration can be stopped while the
bird does something else. This facility adds yet more
variation to the range of annual schedules found among
birds, fitting the various patterns in food availability and
risk to which different migratory populations are exposed
during the year. This variation in annual schedules is shown
mostly in comparisons between species, but also to some
extent between different geographical populations of the
same species. For example, with increasing latitude, the
migrations of many species lengthen, and take up more
of the year, while the periods devoted to breeding and
moult decline in association with the decreasing length
of the favourable season. In some species, populations at
lower latitudes moult in breeding areas, whereas those from
higher latitudes postpone their moult for winter quarters.
Thus, Barn Swallows Hirundo rustica in the southernmost
Moult and plumage 223
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
breeding areas, which are resident or short-distance
migrants, moult during JuneAugust after breeding;
whereas those in the most northerly breeding areas begin
moulting in September–October, after they have reached
their distant wintering areas. At intermediate latitudes
(including Britain and Ireland), varying proportions of
individuals show a split moult, starting in breeding areas,
arresting during migration, and resuming in winter quarters
(Cramp 1988). Likewise, most European populations of
Ringed Plovers Charadrius hiaticula moult rapidly in their
breeding areas in August–September, before migrating
short distances within Europe, whereas arctic-nesting
birds leave their nesting areas after breeding, and postpone
their moult until November–March after reaching their
wintering areas in southern Africa (Stresemann &
Stresemann 1966). Other geographical variants in the
timing and duration of moult occur in many other wader
species, mainly in association with the latitudes at which
they breed and winter (see Cramp & Simmons 1983,
Serra 1998, Underhill 2003). Some species also show sex
differences in the timing of moult and migration, according
to their different parental roles (Newton 2008). Otherwise,
individual variations in the start dates of moult in the
same population relate chiefly to variations in the dates
they finish their preceding activities. Among populations
which moult in their breeding areas, adults that continue
breeding later in the year than others start their moult later,
and young raised late in the year start moulting later than
earlier-hatched young (eg Newton 1966, 1999, Newton &
Rothery 2005, Flinks et al 2008). It is also common for late-
nesting adults to start moulting while they still have young
in the nest, and to replace their feathers more rapidly or
less completely than earlier-moulting individuals. Similarly,
late-fledged juveniles start moulting at an earlier age than
early-hatched ones, thereby lessening the delay in their
migration (Jenni & Winkler 1994, Newton 2008).
Most of our knowledge of moult timing, of the kind
mentioned above, is based on generalisations made from
museum skins. Until the 1960s we had no method of
systematically recording the state and progress of moult
in a way that would enable its timing and duration in a
population to be estimated accurately. However, it was clear
that, in many birds, moult of the primary flight feathers
spanned the whole (or almost the whole) moult period; they
were shed in sequence through the series, so that, for most
of the moult, several primaries were in growth at once, at
different stages. A recording system was therefore devised
in which each primary in one wing was given a score,
according to its stage of growth: old feathers were scored as
0, new ones as 5, and growing ones as 1–4. Adding together
the scores of the different primaries produced a single score
reflecting the stage of moult in the individual concerned
(Ashmole 1962, Evans 1966, Newton 1966). Species with
nine large primaries in each wing scored a maximum of 45
per wing, and species with ten large primaries scored 50.
On this system, the intensity of moult could also be assessed
from the number of flight feathers growing simultaneously
(or from the ‘residual raggedness score’: Bensch & Grahn
1993). Because wings normally moult in step with one
another, it is not necessary to record both. This was the
method used in the British Trust for Ornithology’s moult
recording scheme started in the 1960s.
Regression methods
Plotting the scores of different birds against date enabled
the mean start date and mean rate (or duration) to be
estimated. Regression methods were used in early studies
(Evans 1966, Newton 1966, Ginn & Melville 1983), but
were unsatisfactory because the regression line tends to
run diagonally across the long axis of the parallelogram
enclosing the scatter of points. It effectively gave the
start and end dates for the population as a whole, rather
than for the average bird, thus underestimating the mean
start date and overestimating the mean duration (Pimm
1976, Summers et al 1983). More realistic estimates of
start dates and duration were obtained by calculating the
regression of date on score. Such estimates tend to give
the closest fit to estimates of moult rate obtained from
examining individual birds more than once during moult,
but this approach does not meet some of the assumptions
of standard regression analysis (Underhill & Zucchini
1988). It tends to underestimate mean start date and
overestimate mean duration, especially in populations
in which individuals show wide variation in start dates.
Moreover, regression methods were based only on birds
in active moult, ignoring birds which had not started or
had finished, and thus discarded some potentially useful
Underhill–Zucchini models for avian moult
In response to these problems, Underhill & Zucchini
(1988) proposed a model for avian moult data which made
use of non-moulting as well as moulting birds, fitting the
model using the method of maximum likelihood. They
considered three data types: Type 1, each bird placed in one
of three categories moult not started, in moult and moult
finished; Type 2, each bird classified as in Type 1, except
that moulting birds were given a moult score to reflect the
stage of moult; and Type 3, in which each bird in moult
was given a score, but non-moulting birds were ignored
(as in the early regression methods). The underlying
assumptions were that: (a) birds caught on each day were
224 I. Newton
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
a random sample from the relevant population, (b) the
times of onset of moult followed a specified distribution,
such as the Normal Distribution, and (c) for Type 2 and
Type 3 data the moult score increased linearly with time,
and consistently between individuals.
In an analysis of Bullfinch Pyrrhula pyrrhula moult, the
effects on estimated moult parameters of deviations from
these assumptions were explored using simulated data
(Newton & Rothery 2000). It emerged that only slight
deviation from linearity in Type 3 data had substantial
effects on estimates. The most reliable estimates for this
species were obtained by using Type 1 data, ignoring scores.
Among birds in general, the rate of increase in moult
score is seldom expected to be linear throughout moult,
partly because near the start and end the bird has only one
primary per wing in growth, whereas for the rest of moult
it has up to several at once. The progress of moult would
therefore be expected to follow an S-shaped curve, slower
at the start and end than in the middle (as confirmed in
studies of moult based on captive birds: Newton 1967,
Dawson & Newton 2004).
The problem of non-linearity is accentuated in some
birds, such as waders, in which different primary feathers
vary greatly in length, with long outer ones taking more
than twice as long to grow as short inner ones (Summers et
al 1983). One method devised to correct for this variation
is to weigh each of the primary feathers (obtained from
dead birds), and then correct the scores of living birds to
an appropriate weight of new feather material produced
(Summers et al 1983, Underhill & Joubert 1995).
The total score of a bird obtained visually can then be
converted to a feather mass score, reflecting the percentage
weight of new feather material produced. Such ‘feather
mass scores’ (FMS), or ‘percentage feather mass grown’
(PFMG: Summers et al 1983) generally give a more linear
relationship with date than do the original scores based
on feather lengths (as also confirmed in five species of
passerines: Dawson & Newton 2004). They make a bigger
difference to estimates of moult start dates and durations
for waders, whose feathers vary more in length than those
of most passerines. Some researchers have additionally
allowed for the fact that feathers vary in structure along
their length, calculating a separate weight for each part of
each feather (Redfern 1998). Other potential approaches
to allowing for the non-linearity in the moult score or
PFMG are (a) to transform the data in some way, and (b)
to extend the Underhill–Zucchini model to allow for non-
linear increase in moult scores.
Testing the validity of different methods depends
critically on estimates of the rate of increase in moult
score obtained from individuals caught more than once
during moult. These individual figures give direct measures
of moult rate which are immune to the biases that affect
overall estimates of moult rate obtained from scattergrams
of moult score against date. However, in most studies such
data are limited because few individuals are retrapped.
Comparing Type 1, 2 and 3 values against individual values
for three species (Starling Sturnus vulgaris, Bullfinch and
Sanderling Calidris alba) showed that estimates of start and
end dates (and hence durations) based on Type 1 data were
either better or as good as those obtained using Types 2
and 3 data (Rothery & Newton 2002). Type 1 data are the
easiest to collect because they do not need the allocation of
a moult score or its conversion to mass. The Type 1 method
could also be used for partial moults (including post-
juvenile moult) in which flight feathers are not replaced. It
is easy to implement using the standard binary regression
models that are available in most statistical packages (such
as Minitab Release 12).
Methods that depend on recording non-moulting as well
as moulting birds work well for species that are resident
year-round in the same area, for samples can then be drawn
from the entire population throughout. But sometimes
birds start moulting soon after they have moved into an
area, and stay on later, in which case non-moulting birds
are under-represented in the initial period before all have
arrived. One way round this problem is to restrict analysis
to moulting and post-moult birds, omitting any pre-moult
birds (the Type 4 method of Underhill et al 1990). In
other situations, birds leave on migration after completing
moult, so non-moulting birds are under-represented in the
later period, once the first birds start to leave. In this case
Figure 2. Numerical primary scores of Goldfinches plotted in relation
to date, with the line fitted using the Underhill–Zucchini procedure,
Type 5, which excluded birds that had finished moult (- males; -
females). Mean start date was estimated as 25 July, with 95% of
the birds starting within the 31-day period, 9 July 9 August, and
finishing within the period 22 September 24 October. The mean
duration was 76 days (se = ±4 days). No significant sex differences
emerged. From Newton & Rothery 2009.
Moult and plumage 225
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
analysis is best restricted to pre-moulting and moulting
birds (the Type 5 method of Underhill et al 1990). This
last procedure was used to estimate moult parameters in
Stonechats Saxicola torquatus and Goldfinches Carduelis
carduelis, because it was suspected that many birds left the
study area on completing their moult (Fig 2; Flinks et al
2008, Newton & Rothery 2009).
The Underhill–Zucchini procedure has provided a
means to obtain reliable estimates of moult timing and
rate (and their standard deviations) from only two or three
categories of birds (pre-moult, in moult, post-moult). It has
been used in at least 30 studies so far. In some species in
which it was tested, the Type 1 method gave estimates at
least as reliable as any measures which included the use
of moult scores. However, further testing is required on a
wider range of species, and including separate analyses for
juveniles undergoing body moult alone. Almost certainly,
different models will prove the most appropriate for
different species. This is mainly because species vary in the
extent to which they deviate from each of the assumptions
underlying the models, and different models vary in their
sensitivity to each assumption.
For most European birds we still lack detailed studies of
moult in which the data are adequate for statistical analysis.
Yet moult is one of the easiest things for ringers to record,
especially if they ignore moult scores, and instead place
each bird in one of three categories: pre-moult, in moult,
and post-moult. Providing the population can be sampled
appropriately throughout the moult period, such data
should be sufficient to provide reliable estimates of moult
start dates and durations for the population (with separate
estimates for juveniles changing only their body feathers).
Only with sustained study over the years will we reach a
position in which annual variation and time trends in
these parameters can be examined as a matter of routine.
We now have detailed information on the annual
breeding of many bird species in Britain and Ireland, but
almost nothing on the equivalent annual variation in
moult. What are we missing? How much does the spread
of moult within a population, its timing and duration
vary between years, habitats or regions? And how does
this variation relate to breeding and other events in the
annual cycle, or to environmental variables, including
climate? If we are to venture into this enticing field of
avian ecology, it is bird ringers who must take the lead,
for only they are handling sufficient numbers of live birds
year after year in the same places. Moreover, because of
its close interconnection with breeding and migration,
moult can be used to throw light on aspects of bird ecology
otherwise hard to study. For example, in some multi-
brooded passerine species, the amount of late breeding
can vary greatly from year to year. In species which moult
immediately after breeding (like most British passerines),
this annual variation can be assessed much more easily
by obtaining estimates of moult start dates in different
years than by the more laborious procedure of late-season
nest-searching. Among Bullfinches studied over five years
near Oxford, the proportion of adults which started
moult after 20 August (implying successful breeding from
eggs laid after mid July) varied between 7% and 68% in
different years. End-of-season young-to-adult ratios varied
twofold between years, according to the amount of late
nesting (Newton 1999). This story would not have emerged
without a detailed and fascinating, but undemanding,
study of moult.
I am grateful to Lukas Jenni, Chris Redfern and Peter Rothery,
and an anonymous referee for helpful comments on the
Ashmole. N.P. (1962) The Black Noddy Anous tenuirostris on Ascension
Island. Part I. General Biology. Ibis 103, 235–273.
Bensch, S. & Grahn, M. (1993) A new method for estimating individual
speed of molt. Condor 95, 305–315.
Bensch, S., Hasselquist, D., Hedenström, A. & Ottosson, U.
(1991) Rapid moult among palaearctic passerines in West Africa an
adaptation to the oncoming dry season? Ibis 133, 47–52.
Bluhm, C. (1988) Temporal patterns of pair formation and reproduction
in annual cycles and associated endocrinology in waterfowl. Current
Ornithology 5, 123–185.
Cramp, S. (1988) Handbook of the Birds of Europe, the Middle East and
North Africa. Volume 5. Oxford University Press, Oxford.
Cramp, S. & Simmons, K.E.L. (1977) Handbook of the Birds of
Europe, the Middle East and North Africa. Volume 1. Oxford University
Press, Oxford.
Cramp, S. & Simmons, K.E.L. (1983) Handbook of the Birds of
Europe, the Middle East and North Africa. Volume 3. Oxford University
Press, Oxford.
Dawson, A. & Newton, I. (2004) Use and validation of a molt score
index corrected for primary-feather mass. Auk 121, 372–379.
Evans, P.R. (1966) Autumn movements, moult and measurements of the
Lesser Redpoll Carduelis flammea cabaret. Ibis 108, 183–216.
Flinks, H., Helm, B. & Rothery, P. (2008) Plasticity of moult and
breeding schedules in migratory European Stonechats Saxicola
rubicola. Ibis 150, 687–697.
Ginn, H.B. & Melville, D.S. (1983) Moult in birds. BTO Guide 19.
British Trust for Ornithology, Tring.
Jenni, L. & Winkler, R. (1994) Moult and ageing of European
passerines. Academic Press, London.
Kjellén, N. (1994) Moult in relation to migration in birds a review.
Ornis Svecica 4, 1–24.
226 I. Newton
© 2009 British Trust for Ornithology, Ringing & Migration, 24, 220226
Serra, L. (1998) The adaptation of primary moult to migration and
wintering in the Grey Plover (Pluvialis squatarola), a preliminary
outlook. Biologia e Conservazione della Fauna 102, 123–127.
Serra, L. (2000) How do Palaearctic Grey Plovers adapt primary moult
to time constraints? An overview across four continents. Wader Study
Group Bulletin 93,11–12.
Stresemann, E. & Stresemann, V. (1966) Die Mauser der Vögel.
Journal für Ornithologie 107, 3–448.
Summers, R.W., Swann, R.L. & Nicoll, M. (1983) The effects of
methods on estimates of primary moult duration in the Redshank Tringa
totanus. Bird Study 30, 149–156.
Underhill, L.G. (2003) Within ten feathers: primary moult strategies
of migratory waders (Charadrii). In Avian Migration (eds Berthold,
P., Gwinner, E. & Sonnenschein, E.), pp 187–197. Springer-Verlag,
Underhill, L. & Joubert, A. (1995) Relative masses of primary feathers.
Ringing & Migration 16, 109–116.
Underhill, L.G. & Summers, R.W. (1993) Relative masses of primary
feathers in waders. Wader Study Group Bulletin 71, 29–31.
Underhill, L.G. & Zucchini, W. (1988) A model for avian primary
moult. Ibis 130, 358–372.
Underhill, L.G., Zucchini, W. & Summers, R.W. (1990) A model
for avian primary moult data types based on migration strategies and
an example using the redshank Tringa totanus. Ibis 132, 118–123.
Newton, I. (1966) The moult of the Bullfinch Pyrrhula pyrrhula. Ibis
108, 41–67.
Newton, I. (1967) Feather growth and moult in some captive finches.
Bird Study 14, 10–24.
Newton, I. (1969) Moults and weights of captive Redpolls. Journal für
Ornithologie 110, 53–61.
Newton, I. (1999) An alternative approach to the measurement of
seasonal trends in bird breeding success: a case study of the Bullfinch
Pyrrhula pyrrhula. Journal of Animal Ecology 68, 698–707.
Newton, I. (2008) The migration ecology of birds. Academic Press,
Newton, I. & Marquiss, M. (1982) Moult in the Sparrowhawk. Ardea
70, 163–172.
Newton, I. & Rothery, P. (2000) Timing and duration of moult in
the Bullfinch Pyrrhula pyrrhula: an appraisal of different analytical
procedures. Ibis 142, 65–74.
Newton, I. & Rothery, P. (2005) The timing, duration and pattern of
moult and its relationship to breeding in a population of the European
Greenfinch Carduelis chloris. Ibis 147, 667–679.
Newton, I. & Rothery, P. (2009) Timing and duration of moult in adult
European Goldfinches. Bird Study 56, 282–288.
Pimm, S. (1976) Estimation of the duration of bird molt. Condor 78,
Redfern, C.P.F. (1998) The analysis of primary moult using feather mass.
Ringing & Migration 19, 39–40.
Rothery, P. & Newton, I. (2002) A simple method for estimating
timing and duration of avian primary moult using field data. Ibis
144, 526–528.
... Moult is considered one of the three most energydemanding (and time-limited) processes in the avian life cycle (Lindstr€ om et al. 1993); the two other activities are breeding and migration (Newton 2009, Bridge 2011. While breeding and moult are essential in all bird species, migration occurs in a minority of species (about 20% of bird species; Kirby et al. 2008). ...
An understanding of feather moult, an important process in the life cycle of birds, lags behind that of other avian life‐history events. This lag includes a lack of scientific attention, but surprisingly also a lack of basic knowledge regarding the moult strategy of many bird species. This situation is particularly astonishing in light of the fact that feathers are a unique characteristic of birds. Currently, there are two main terminology systems for describing moult: one life‐cycle‐based and one plumage‐based (H–P terminology). A survey conducted among 434 birdwatchers, bird‐ringers (banders) and ornithologists showed a significant difference in understanding of the two terminologies. Ornithologists studying moult, as well as editors and reviewers, are called upon to make use of, and encourage the use of, understandable moult terminology, as much as possible. Using more understandable terms and language may help a wider audience of amateurs, students and ornithologists to understand moult. Involvement of a wider audience may advance data collection and research of this important event in the avian life cycle.
... It defines the timing and duration of growth, reproduction, and other life-cycle events and thereby determines the ability of organisms to capture seasonally variable resources (Chuine & Régnière 2017). Most adult birds replace all of their feathers once a year, and this process, known as moult, provides an energetic challenge in the annual cycle on a par with major events like reproduction and migration (Newton 2009). Despite this, moult has been a neglected subject in ornithology and much remains to be learned about how it fits into the annual cycle of birds. ...
Full-text available
Feather replacement during moult is an energetically demanding stage of birds' annual cycles. Despite this moult remains a neglected field of study in ornithology. This may in part be because the analysis of moult observations requires non-standard statistical techniques. We present moultmcmc an R package implementing Bayesian inference for models of avian moult phenology using fast Hamiltonian Monte Carlo sampling. Our package expands on existing maximum likelihood methods by accommodating repeat measures data, and by facilitating the joint analysis of different moult data types. We describe the theory behind moult phenology models and demonstrate their application using simulated and real world data. The moultmcmc package provides an interface for modelling moult phenology data from typical real world datasets and thereby further facilitates the uptake of appropriate statistical methods for these data.
... parasites), poor weather, nutritional challenges, collisions and abrasions from the environment [3]. As feathers are dead structures and cannot repair themselves, birds will replace worn and missing feathers through an energetically demanding and lengthy moulting process [4][5][6]. ...
Full-text available
Ground-dwelling species of birds, such as domestic chickens ( Gallus gallus domesticus ), experience difficulties sustaining flight due to high wing loading. This limited flight ability may be exacerbated by loss of flight feathers that is prevalent among egg-laying chickens. Despite this, chickens housed in aviary style systems need to use flight to access essential resources stacked in vertical tiers. To understand the impact of flight feather loss on chickens' ability to access elevated resources, we clipped primary and secondary flight feathers for two hen strains (brown-feathered and white-feathered, n = 120), and recorded the time hens spent at elevated resources (feeders, nest-boxes). Results showed that flight feather clipping significantly reduced the percentage of time that hens spent at elevated resources compared to ground resources. When clipping both primary and secondary flight feathers, all hens exhibited greater than or equal to 38% reduction in time spent at elevated resources. When clipping only primary flight feathers, brown-feathered hens saw a greater than 50% reduction in time spent at elevated nest-boxes. Additionally, brown-feathered hens scarcely used the elevated feeder regardless of treatment. Clipping of flight feathers altered the amount of time hens spent at elevated resources, highlighting that distribution and accessibility of resources is an important consideration in commercial housing.
Banding data are commonly used to estimate vital rates for migratory game bird management. We used white‐winged dove ( Zenaida asiatic a) banding data to estimate molt and hatch chronology in Texas. We used Texas Parks and Wildlife Department's long‐term, state‐wide banding data (71,675 banded individuals) from 1 June to 15 August 2007–2016 to investigate primary feather molt and hatching in white‐winged doves in Texas. We estimated primary feather molt and used individual recapture data to determine reliability of models predicting primary feather molt rates. For hatching, we used primary feather molt scores of captured hatch‐year doves to backdate to an estimated hatch date. Our modeling predicted mean after‐hatch‐year primary feather molt rate of 13.21 ± 0.93 days. We predicted 95% of adult white‐winged doves began molting between 7 April to 8 July and completed molt between 17 August to 17 November. Across all years, white‐winged doves hatched as early as 6 January and as late as 27 July, with 95% of all hatching occurring between 22 March and 18 June and peaking on 4 May. Primary feather molt initiation peaked 16 days after the peak of hatching, suggesting that white‐winged doves delay the onset of primary molt until reproductive activity slows. Secondary data collected during banding operations on migratory game birds may be used to understand additional life processes without the requirement to initiate additional survey efforts.
Full-text available
In monomorphic species, like in the Black-headed Gull, both sexes look alike in breeding plumage. With large sets of data on captured and photographed birds and using the Underhill–Zucchini moult model, we provided a detailed pattern of breeding plumage development in this species by age and sex. This study, similar to other studies, documented first adults with the initial stage of head moult at the beginning of January, yet the mean start date of nuptial moult in adults was the end of February. Half of adults acquired full breeding plumage about mid-March and almost all of them before mid-April. The start date of nuptial moult was more variable in immatures. The mean start of head moult in immatures was 19th April, which is 52 days later than in adults, and the majority, i.e., 70%, did not complete moult until the end of May. We showed for the first-time sex-dependent breeding plumage acquisition in monomorphic species. According to the Underhill–Zucchini moult model, males started to moult on average 7 days earlier than females and their moult lasted 7 days longer. Hence, the final date of completed head moult was the same in both sexes. A fully developed hood is an important part of the status signalling during pairing; therefore, completing the moult before mating is important for both sexes.
We studied the primary moult of immature and adult breeding Common Swift Apus apus in Italy. Birds were sampled at breeding colonies, or by attracting them to mist nets with the playback of recorded calls. Our sample of 590 immatures (2cy) assessed that about a quarter (25.6%) of these birds start moulting the inner primaries during their stay in Europe. We find that this moult starts usually in the second half of June, earlier than was observed in other European countries, where individuals begin moulting in July. Interestingly, and in contrast to previous knowledge on the moulting schedules of breeding Common Swifts, we found that more than half of breeding adults (56%, 15 of 27) started their primary moult in July. Moult before the swifts left our study area was limited to the first two inner primaries. Our study showed that breeding Commons Swifts are able to regulate their moult when already engaged in rearing young, and both immature and adult Swifts start their moult before leaving Europe towards their African winter quarters.
Full-text available
In this study, the annual movements of a seabird species, the red-throated diver (Gavia stellata), were investigated in space and time. Between 2015 and 2017, 33 individuals were fitted with satellite transmitters at the German Bight (eastern North Sea). In addition, stable isotope analyses of feathers (δ13C) were used to identify staging areas during the previous moult. The German Bight is an important area for this species, but is also strongly affected by anthropogenic impacts. To understand how this might affect populations, we aimed to determine the degree of connectivity and site fidelity, and the extent to which seasonal migrations vary among different breeding locations in the high Arctic. Tagged individuals migrated to Greenland (n = 2), Svalbard (n = 2), Norway (n = 4) and northern Russia (n = 25). Although individuals from a shared breeding region (northern Russia) largely moved along the same route, individuals dispersed to different, separate areas during the non-breeding phase. Kernel density estimates also overlapped only partially, indicating low connectivity. The timing of breeding was correlated with the breeding longitude, with 40 days later arrival at the easternmost than westernmost breeding sites. Repeatability analyses between years revealed a generally high individual site fidelity with respect to spring staging, breeding and moulting sites. In summary, low connectivity and the distribution to different sites suggests some resilience to population decline among subpopulations. However, it should be noted that the majority of individuals breeding in northern Russia migrated along a similar route and that disturbance in areas visited along this route could have a greater impact on this population. In turn, individual site fidelity could indicate low adaptability to environmental changes and could lead to potential carry-over effects. Annual migration data indicate that conservation planning must consider all sites used by such mobile species.
Avian cold adaptation is hallmarked by innovative strategies of both heat conservation and thermogenesis. While minimizing heat loss can reduce the thermogenic demands of body temperature maintenance, it cannot eliminate the requirement for thermogenesis. Shivering and non‐shivering thermogenesis (NST) are the two synergistic mechanisms contributing to endothermy. Birds are of particular interest in studies of NST as they lack brown adipose tissue (BAT), the major organ of NST in mammals. Critical analysis of the existing literature on avian strategies of cold adaptation suggests that skeletal muscle is the principal site of NST. Despite recent progress, isolating the mechanisms involved in avian muscle NST has been difficult as shivering and NST co‐exist with its primary locomotory function. Herein, we re‐evaluate various proposed molecular bases of avian skeletal muscle NST. Experimental evidence suggests that sarco(endo)plasmic reticulum Ca2+‐ATPase (SERCA) and ryanodine receptor 1 (RyR1) are key in avian muscle NST, through their mediation of futile Ca2+ cycling and thermogenesis. More recent studies have shown that SERCA regulation by sarcolipin (SLN) facilitates muscle NST in mammals; however, its role in birds is unclear. Ca2+ signalling in the muscle seems to be common to contraction, shivering and NST, but elucidating its roles will require more precise measurement of local Ca2+ levels inside avian myofibres. The endocrine control of avian muscle NST is still poorly defined. A better understanding of the mechanistic details of avian muscle NST will provide insights into the roles of these processes in regulatory thermogenesis, which could further inform our understanding of the evolution of endothermy among vertebrates.
Full-text available
Full-text available
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.
Full-text available
Population-level insights into how a species incorporates moult into its annual cycle is an important component of understanding the time constraints on the migration system of the species. In this respect, the key parameters of moult in a population are the average starting date and duration. These parameters need to be seen in the context of the timing of the other major events in the annual cycle, breeding and migration. For moult studies in many species, it is appropriate initially to focus on the moult of the primary wing feathers, because the main annual moult of many other feather tracts takes place within the period of moult of the primaries.
Full-text available
In European Starlings (Sturnus vulgaris), mass of new primary feathers increases linearly with time for most of the duration of molt (Dawson 2003). Here, we had two aims: (1) to confirm that mass of new primary feathers increases linearly in other species, and (2) to use that linear increase as the basis of a system to score the progress of molt. Increase in length of primary feathers during molt was recorded for captive Eurasian Magpies (Pica pica), Carrion Crows (Corvus corone), European Greenfinches (Carduelis chloris), and Eurasian Bullfinches (Pyrrhula pyrrhula). Wing shape differs among those species. Feather lengths during molt were converted into mass by using information on final feather length and mass and the distribution of mass from tip to base of feather. Rate of increase in total mass of new primary feathers was largely linear in all four species. A molt scoring method is described in which individual feather scores are weighted to account for the contribution of each particular primary feather's mass toward total primary-feather mass. When the method was tested on eight captive starlings, the increase in mass-corrected molt score was almost linear, unlike the increase shown by the standard scoring system, which exaggerated molt rate during the early part of molt and underestimated it later. In the four species studied here, mass-corrected molt score likewise closely tracked the actual increase in mass, unlike the standard molt score. Because it is based on feather mass, the method presented here is of greater physiological and energetic relevance than the standard method. Because the mass-corrected score increases more linearly with time, it has the additional advantage of enabling less complicated, and potentially more accurate, estimations of molt start dates and molt durations.
Most species tend to avoid moult during breeding. Most short-distance migrants change their feathers in summer before autumn migration, while most long-distance migrants perform a winter moult in the tropics after autumn migration. A complete moult both in summer and winter has only been recorded in a few passerines. Birds like albatrosses and larger eagles have a serial moult, changing only a number of their primaries every year. Another strategy common among long-distance migrants is to change some feathers on the breeding grounds, suspend moult, and complete it in the winter quarters. A special adaptation allowing faster moult is the simultaneous shedding of all wing quills. During this time birds are flightless and many species perform spectacular moult migrations to congregate in areas rich in food and free of predators. A comparative study of three different groups (raptors, waders and warblers) is presented. -from Author
This book presents an up-to-date, detailed and thorough review of the most fascinating ecological findings of bird migration. It deals with all aspects of this absorbing subject, including the problems of navigation and vagrancy, the timing and physiological control of migration, the factors that limit their populations, and more. Author, Ian Newton, reveals the extraordinary adaptability of birds to the variable and changing conditions across the globe, including current climate change. This adventurous book places emphasis on ecological aspects, which have received only scant attention in previous publications. Overall, the book provides the most thorough and in-depth appraisal of current information available, with abundant tables, maps and diagrams, and many new insights. Written in a clear and readable style, this book appeals not only to migration researchers in the field and Ornithologists, but to anyone with an interest in this fascinating subject. * Hot ecological aspects include: various types of bird movements, including dispersal and nomadism, and how they relate to food supplies and other external conditions * Contains numerous tables, maps and diagrams, a glossary, and a bibliography of more than 2,700 references * Written by an active researcher with a distinguished career in avian ecology, including migration research.
When breeding and nesting behavior in birds is considered within the larger framework of the annual cycle, it is evident that reproduction may be tightly linked to the progression and timing of preceding events, such as migration and molt. Furthermore, when the physiological bases of the separate events in the annual cycle are then considered and interwoven, yet another dimension of relationships emerges. The relationships are those of physiological systems that control cycles of molt, migration, and gonadal growth. This is not, however, a novel approach, and it has been advocated by others (Farner and Follett, 1966, 1979; Lofts and Murton, 1968, 1973; Wingfield and Farner, 1980). The main purpose of this review is to integrate the recent advances in environmental endocrinology and behavioral ecology of waterfowl. The Anatidae comprise a family of related species that exhibit different ecological requirements, variable social behavior, and diversity in the temporal relationships between pair formation and nesting. My first objective is to summarize the recent literature on temporal chronology of reproduction of waterfowl to determine what general patterns exist. My second objective is to provide a review of the current knowledge of reproductive endocrinology of waterfowl for all stages of the annual cycle. An integration of the two areas should reveal new insights about differences in physiology and their relationship to reproductive strategies.
We introduce a new method, Residual Raggedness Value (RRV), for estimating molt duration for individual birds captured only once during a molting period. The method is developed and tested using data from Willow Warblers (Phyiloscopus trochilus) in prebasic (post-nuptial) molt collected in Swedish Lapland during 1983-l 990. The wing raggedness value (RV) describes the amount of "missing" feather area in the wing of a molting bird. RV was positively correlated with stage of molt. The RRVs from this correlation were used to ob?ain an estimate of the size of the gap in the wing that was independent of stage of molt (i.e., RV controlled for stage of molt). Molt speed of recaptured birds was highly correlated with RRV at the first capture (rL = 0.57). Thus, an individual' s future molt speed could be predicted at the first capture with a high degree of accuracy. Compared to other methods for estimating molt duration, the RRV method produced estimates close to those obtained from recaptured birds. The widely used regression method for estimating molt duration (regressing date of capture on molt score) gave estimates that deviated substantially from both those obtained from the recapture and RRV methods. Our new method is a potentially powerful tool for increasing sample sizes of individual molt speeds in a studied population. This will facilitate understanding how individual birds may adjust the timing and duration of molt m relation to breeding and migration. The RRV method is probably applicable to most species that molt feathers sequentially. However, slow-molting species with few simultaneously growing feathers might be problematic.