Rapid flight feathers moult and fat stores in the Common Snipe Gallinago gallinago in the early stage of autumn migration

Abstract

We analysed primary and secondary feather moult and fat reserves in 539 Common Snipes captured in the middle Pripyat River Valley, an important stopover site for waders in Central Europe, between 2002 and 2022. The average daily rate of feather growth was 1.89% in primaries and 2.27% in secondaries, being one of the highest documented in waders. The estimated duration of growth for a single flight feather varied from 11 to 21 days in primaries and from 8 to 11 days in secondaries. Moreover, multiple flight feathers (up to 14) were replaced simultaneously. As a result, the wing moult in Common Snipes was rapid with the mean primary moult duration estimated at 53 days (28 June–20 August) according to the Underhill–Zucchini model, and only 20 days in secondaries (31 July–20 August) based on moult estimates of individual secondaries. Hence, although secondary feathers began to grow when primary moult was already advanced, moulting of both flight feather groups was completed in most birds at almost the same time. Our study shows that Common Snipe in the middle Pripyat River Valley exhibit very rapid wing moult with large wing gaps. Fat reserves and thus body mass of Common Snipes were the lowest when the wing gap was greatest, compensating for their reduced wing area. Late and slow movement towards wintering grounds, allows them to moult rapidly at the early stage of autumn migration, which is likely to occur only in sites with abundant food resources.

Full text

Vol.:(0123456789)
Journal of Ornithology
https://doi.org/10.1007/s10336-024-02171-2
ORIGINAL ARTICLE
Rapid flight feathers moult andfat stores intheCommon Snipe
Gallinago gallinago intheearly stage ofautumn migration
PavelPinchuk1· WłodzimierzMeissner2
Received: 24 October 2023 / Revised: 22 February 2024 / Accepted: 11 March 2024
© The Author(s) 2024
Abstract
We analysed primary and secondary feather moult and fat reserves in 539 Common Snipes captured in the middle Pripyat
River Valley, an important stopover site for waders in Central Europe, between 2002 and 2022. The average daily rate of
feather growth was 1.89% in primaries and 2.27% in secondaries, being one of the highest documented in waders. The
estimated duration of growth for a single flight feather varied from 11 to 21days in primaries and from 8 to 11days in
secondaries. Moreover, multiple flight feathers (up to 14) were replaced simultaneously. As a result, the wing moult in
Common Snipes was rapid with the mean primary moult duration estimated at 53days (28 June–20 August) according to
the Underhill–Zucchini model, and only 20days in secondaries (31 July–20 August) based on moult estimates of individual
secondaries. Hence, although secondary feathers began to grow when primary moult was already advanced, moulting of
both flight feather groups was completed in most birds at almost the same time. Our study shows that Common Snipe in
the middle Pripyat River Valley exhibit very rapid wing moult with large wing gaps. Fat reserves and thus body mass of
Common Snipes were the lowest when the wing gap was greatest, compensating for their reduced wing area. Late and slow
movement towards wintering grounds, allows them to moult rapidly at the early stage of autumn migration, which is likely
to occur only in sites with abundant food resources.
Keywords Waders· Moult migration· Primary moult· Secondary moult· Wing gap· Fat score
Zusammenfassung
Schnelle Schwungfedermauser und Fettreserven bei der Bekassine Gallinago gallinago zu Beginn des Herbstzuges
Wir analysierten die Mauser der primären und sekundären Schwungfedern sowie die Fettreserven von 539 Bekassinen, die
zwischen 2002 und 2022 im mittleren Tal des Flusses Pripjat gefangen wurden, einem wichtigem Rastgebiet für Watvögel
in Mitteleuropa. Die durchschnittliche tägliche Wachstumsrate der primären Schwungfedern betrug 1,89% und die der
sekundären Schwungfedern 2,27%, eine der höchsten Wachstumsraten, die bei Watvögeln bisher dokumentiert wurden. Die
geschätzte Wachstumsdauer für einzelne primäre Schwungfedern variierten zwischen elf und 21 Tagen und für sekundäre
Schwungfedern zwischen acht und elf Tagen. Außerdem wurden mehrere Schwungfedern (bis zu 14) gleichzeitig erneuert.
Nach dem Underhill-Zucchini-Model verlief die Flügelmauser bei den Bekassinen also sehr schnell, mit einer geschätzten
durchschnittlichen Mauserdauer von 53 Tagen (28. Juni bis 20. August) für primäre Schwungfedern und nur 20 Tagen (31.
Juli bis 20. August) für sekundäre Schwungfedern. Obwohl die sekundären Schwungfedern erst zu wachsen begannen, als
die Mauser der primären Schwungfedern bereits weit fortgeschritten war, wurde die Mauser der beiden Flugfedergruppen bei
den meisten Individuen fast gleichzeitig abgeschlossen. Unsere Studie zeigt, dass Bekassinen im mittleren Tal des Flusses
Communicated by F. Bairlein.
* Włodzimierz Meissner
w.meissner@ug.edu.pl
1 National Park “Pripyatsky”, Turov, Belarus
2 Ornithology Unit, Department ofVertebrate Ecology
andZoology, Faculty ofBiology, University ofGdańsk, Wita
Stwosza 59, 80-308Gdańsk, Poland

Journal of Ornithology
Pripjat eine schnelle Flügelmauser mit großen Lücken in den Flügeln vollziehen. Die Fettreserven und damit die Körpermasse
der Bekassinen waren am geringsten, als die Lücken im Flügel am größten waren, um die verringerte Flügelfläche zu
kompensieren. Späte und langsame Zugbewegungen in Richtung der Überwinterungsgebiete ermöglichen es den Bekassinen,
zu Beginn des Herbstzuges schnell zu mausern, was wahrscheinlich nur dort geschieht, wo es reichliche Nahrungsressourcen
gibt.
Introduction
The wing moult is an important stage in migrants’ annual
cycle. The loss of wing area due to missing and/or not fully
grown primaries and secondaries increases wing loading
and may impair flight performance (Rayner 1988; Swad-
dle and Witter 1997; Hedenström 2003). Therefore, the
timing of the flight feather replacement rarely coincides
with such an energy-demanding stage of the annual cycle
as migration (Kjellén 1994). Even though birds may com-
pensate for increased wing loading by reducing their body
mass (Holmgren etal. 1993; Swaddle and Witter 1997; Lind
and Jakobsson 2001), migrants need to accumulate energy
reserves (mainly fat) for non-stop migratory flights (Berthold
1993). Hence, there is a trade-off between the necessity to
increase body mass before migratory flight and reduced wing
area during feather moult. In waders, for example, active pri-
mary feather moult during migration was recorded mainly
in short- and medium-distance migratory species (i.e.,
Snow and Snow 1976; Meissner and Huzarski 2006, but see
Holmgren etal. 1993). Whereas trans-equatorial migrants
complete flight feathers replacement in wintering grounds,
and adjust it to the abundance of food (Remisiewicz etal.
2009; Barshep etal. 2013) or prior migratory flight (Holmes
1966; Owen and Krohn 1973). The primary feather moult
may also start on the breeding grounds, later may be sus-
pended for migration, and resumed after the arrival to win-
tering grounds (Serra etal. 2006). Hence, waders display a
wide variety of flight feather moult strategies (Remisiewicz
2011; Jackson and Underhill 2022), with the duration of
moult being the key factor determining feather durability.
Flight feathers that grow slowly are of better quality and last
longer than feathers that are grown rapidly (Dawson etal.
2000; Serra 2001). Another moult strategy recorded in many
waterfowl (i.e., Panek and Majewski 1990; Köhler and von
Krosigk 2006; Fox etal. 2014) is the so-called moult migra-
tion, in which flight feather replacement starts and is at least
partially completed on a staging area, after a post-breeding
migratory movement. The moult migration has been found
also in some waders (Hoffmann 1957; Jehl Jr 1987; OAG
Münster 1991; Barbaree etal. 2016). However, unlike water-
fowl, waders retain the ability to fly during flight feathers
moult but may exhibit reduced flight performance due to
the presence of a gap in the wing area, which makes them
more vulnerable to predation (Swaddle and Witter 1997;
Swaddle etal. 1999).
Primaries and secondaries have different functions in a
bird's wing. The lift is generally produced by the inner wing
by creating the airfoil shape of the bird's wing, as air moves
over the surfaces of the secondaries, whereas thrust is pro-
duced by the primaries of the outer wing mostly generated
on the downstroke of flapping flight (Azuma 1992; Dvořák
2016). However, our knowledge of the moult pattern of sec-
ondaries in waders is sparse as they are usually omitted in
moult studies that mostly focus on the primary replacement
(but see: Henriksen 1985; Summers etal. 2004).
The Common Snipe Gallinago gallinago is a migratory
wader that breeds throughout northern Eurasia and migrates
in large numbers toward wintering grounds in southwestern
Europe and northwestern Africa (Glutz von Blotzheim etal.
1977; Minias etal. 2010). This species adopts the B-strat-
egy of migration (sensu Alerstam and Hӧgstedt 1982), i.e.,
faces strong interspecific competition on their wintering
grounds, their autumn migration starts late and is strongly
influenced by worsening weather conditions (Alerstam and
Hӧgstedt 1982; Włodarczyk etal. 2007), with adults and
juveniles migrating at the same time (Pinchuk etal. 2007).
The flight feather replacement in the Common Snipe starts
at the breeding ground or at the onset of migration, with
birds arriving at wintering grounds after completing the
flight feathers’ and body feathers’ moult (Glutz von Blotz-
heim etal. 1977). The most comprehensive analysis of flight
feather replacement in this species has been provided by the
OAG Münster (1975). However, due to the lack of modern
statistical methods that study is only descriptive.
This study aims to estimate the start, duration, and
variation in the start date of primary and secondary moult
using advanced methods based on the Underhill–Zucchini
model (Underhill and Zucchini 1988; Underhill etal. 1990)
in Common Snipe staging in the Middle Pripyat Valley in
Central Europe. The application of this model enables a
far more detailed insight into the flight feathers’ moult, its
progress over time, and variation in the moult rate of indi-
vidual feathers. As the accumulation of fat reserves is crucial
for the beginning of the migratory flight and the gap in the
wing area increases the energetic cost of flight (Hedenström
2003), we also focus on the influence of the wing gap size
on the amount of fat stores accumulated by Common Snipe
at this early stage of their migration.

Journal of Ornithology
Methods
Study area
Studies were conducted in the floodplain meadows of the
Pripyat River near Turov, Gomel Region, Belarus (N 52°
04′, E 27° 44′) (Fig.1). This is an important stopover site
for waders during spring and autumn migrations (Meissner
etal. 2011; Pinchuk and Karlionova 2011; Pinchuk etal.
2016). The Common Snipe breeds there in low densities,
i.e., between 0.5 and 3.7 pairs/km2 ha, where grass com-
munities are predominant (Mongin 2002; authors’ unpub-
lished data). From mid-June, the number of Common Snipe
in the floodplain meadows increases rapidly, reaching a daily
maximum of up to 400–500 individuals in the trapping area,
i.e., a small peninsula of about 0.6–0.7 km2 formed by the
Pripyat River and a small tributary (authors’ unpublished
data).
Field study
The field study was conducted over 11 consecutive seasons,
from 2002 to 2022. Birds were captured at different times
and with different intensities from mid-June to mid-Octo-
ber. To maximise the number of captured snipes different
catching methods were used. Walk-in traps were located on
riverine islands and wet meadows during the whole study
period. In some years, playback calls were used through the
night to attract Common Snipe to the catching site. Birds
staying there were flushed to mist nets every hour (Pinchuk
and Karlionova 2006). Birds were aged according to plum-
age characteristics, and only adult snipes were considered, as
juveniles do not moult flight feathers during autumn migra-
tion (Włodarczyk etal. 2008). Three individuals with sus-
pended primary moult and uninitiated secondary moult were
excluded from the analysis. In total, 539 individuals were
used in the analyses. In two birds, a moult of secondaries
was not recorded (Table1).
Fig. 1 Location of the study area in the middle Pripyat River Valley near Turov (black dot)
Table 1 The number of Common Snipe in three different stages of
primary and secondary moult
Flight feathers Not started
moult In moult Finished moult Total
Primaries 6 381 152 539
Secondaries 185 197 155 537

Journal of Ornithology
The amount of subcutaneous fat was assessed accord-
ing to an eight-point scale developed for waders (Meiss-
ner 2009). Every year, the accuracy and repeatability of
measurements taken by different ringers were checked as
described by Busse and Meissner (2015).
Moult analysis
As primaries and secondaries have different functions dur-
ing the flight, in this study, their moult pattern has been
analysed separately, with the results of the two analyses
compared. We used the standard moult formula, where the
moult stage of each of the ten primaries and ten secondaries
was recorded as a score between 0 (old feather) and 5 (new
full-grown feather) (Ashmole 1962). Because the outer pri-
maries are heavier than the inner ones and the distribution of
their moult scores is not linear (Summers 1980), the moult
scores were converted to Percentage of Primary Feather
Mass Grown (PPFMG), where feathers that had moult scores
of 1, 2, 3, 4 and 5 were given a corresponding moult index
of 0.125, 0.375, 0.625, 0.875 and 1, respectively (Underhill
and Zucchini 1988). The mean percentage mass for each
primary of the studied species needed for this transformation
was taken from Meissner etal. (2018). Consequently, the
same procedure was applied to secondaries, despite small
differences in their masses (Table2). Secondaries were col-
lected from three birds found dead, dried to constant mass
in a convection oven at 60°C, and then weighed, as rapidly
as possible after drying, to an accuracy of 0.1mg using an
electronic balance as described by Meissner etal. (2018).
The moult scores of secondaries were converted to the Per-
centage of Secondary Feather Mass Grown (PSFMG) same
as in primaries.
The proportion of individuals that had completed primary
moult (PPMFG = 1) and not initiated moulting (PPFMG = 0)
was unequal (Table1). Therefore, some Common Snipe
began replacing their primary flight feathers before arriv-
ing at the study area. Hence, the Type 4 moult model for
birds in active moult and those that have completed their
moult was applied (Underhill and Zucchini 1988; Underhill
etal. 1990). The moult parameters of secondaries were esti-
mated using the Type 2 moult model because individuals in
all three moult stages were present in the collected sample,
i.e., not yet moulting their secondaries, in active secondary
moult, and birds, which have completed their secondary
moult (Table1). Consistently, when estimating the moult
parameters for individual primaries and secondaries, the
moult model Type 4 was applied to the two innermost prima-
ries and the moult model Type 2 to the remaining primaries
and secondaries. To compare the growth rate of primaries
and secondaries, we calculated the daily rate of feather mate-
rial growth (FMG/day) by dividing the relative mass of all
primaries or secondaries by the estimated duration of moult.
The ratio of the relative mass of each flight feather to its
estimated duration of moult provided an estimate of its daily
growth rate expressed as a percent of PPFMG and PSFMG
per day (Serra 2000; Underhill 2003). Using estimated start-
ing and ending dates of moult for each flight feather with
their daily growth rate, we plotted their cumulative growth
during the moult, assuming that daily growth values are con-
stant (Underhill and Zucchini 1988).
We estimated the Proportion of Flight Feather Mass Miss-
ing (PFFMM), where feathers with moult scores of 1, 2, 3
and 4 are assumed to represent 0.875, 0.625, 0.375 and 0.125
of the relative feather mass missing, respectively, i.e., the
missing relative mass of each of the primary and secondary
flight feather. After summing up these values, we obtained
an assessment of the amount of missing wing area due to
moult, i.e., wing gap (Ward etal. 2007; Barshep etal. 2013).
Similar to Podlaszczuk etal. (2016), we used a fat score
as an index of body condition because the lean body mass
of birds during the moult may change considerably (Murphy
and King 1992; Lind etal. 2004), including the ratio of pec-
toral muscle size to body mass (Lind and Jakobsson 2001).
Whereas visible subcutaneous fat reflects an approximately
linear increase in fat mass in waders (Meissner 2009). Divi-
sion of the year into 5-day periods followed Berthold (1973).
Our study sample included birds caught with walk-in
traps during the day and mist-nets with playback calls dur-
ing the night, which may lead to a mix of birds in different
body condition, i.e., those that have stopped in the study area
and active migrants lured to land (Figuerola and Gustamante
1995). A Generalized Linear Model (GLM) (McCullagh and
Nelder 1989) was applied to check for the differences in fat
score, primary and secondary moult advancement (continu-
ous, response variables) between birds caught during the
day and birds caught at night with playback calls (categori-
cal, explanatory variable) in the following 5-day periods
Table 2 Absolute and relative
masses of the Common Snipe
secondaries (N = 3)
Secondary number
Outer Inner
1 2345678910
Mean mass (mg) 66.5 68.8 68.3 68.0 67.5 68.0 68.5 69.5 70.3 71.0
Relative mass (%) 9.7 10.1 9.9 9.9 9.8 9.9 10.1 10.1 10.2 10.3

Journal of Ornithology
(continuous, explanatory variable). The latter was the only
statistically significant variable influencing fat score, PFMG,
and SFMG, while the capture method was insignificant in
all three models (TableS1). Hence, data on birds captured
with playback calls and without luring were combined in
further analyses.
Results
At the beginning of the field study period, in June, the
majority (83%) of Common Snipe that were captured had
growing primaries. The first individual with a completed
moult of primaries was caught on 28th July, and the bird
with all primaries and secondaries moulted was observed
on 1st August. The time of primary and secondary moult
largely overlap (Fig.2). The mean primary moult duration
was estimated at 53days, lasting from 28th June to 20th
August, while the mean moult duration for secondaries was
44days, nine days shorter, starting on 29th July and ending
on 11th September (Fig.2, Table3). As a result, secondar-
ies had a higher daily rate of feather material growth than
primaries (Table3). In contrast to PPFMG, the distribution
of PSFMG values over time deviates from a linear with a
group of high values in birds captured in July (Fig.2B).
Consequently, the variance in moult duration according to
the standard deviation parameter of Underhill and Zucchini
(1988) model was about 6days larger for secondaries than
for primaries (Table3). This means that in the case of sec-
ondaries, the UZ moult model cannot estimate moult param-
eters well and the presented average values for the start date,
duration, and end date (Table3) should be regarded as a very
approximate. However, the distribution of PSFMG values
over time with great daily rate of the feather material growth
clearly indicated a very high feather replacement rate.
The primaries were shed sequentially from innermost to
outermost, and the number of growing flight feathers grad-
ually increased till P5, then slightly decreased when pri-
maries from sixth to eighth have been shed (Fig.3). When
the innermost secondary was shed, the number of growing
flight feathers was still low and later distinctly increased
with the fall of two subsequent secondaries (Fig.3). Just
after the start of the secondary moult, the median number of
simultaneously growing flight feathers reached 12 (with the
Fig. 2 Temporal distribution
of the Proportion of Primary
Feather Mass Grown (PPFMG)
(A) and Proportion of Sec-
ondary Feather Mass Grown
(PSFMG) (B) for Common
Snipe. Solid lines—the mean
course of the primary and sec-
ondary moult, dashed lines—
95% confidence intervals
0.0
0.2
0.4
0.6
0.8
1.0
Prop ortion of primaryfeather mass grow n(PPFMG)
8Aug
28
Aug
17
Sep
7Oct
19 Jul
29 Jun
9Jun
A
0.0
0.2
0.4
0.6
0.8
1.0
Prop or tion of secondaryfeather ma ss grown(PSFMG)
8Aug
28 Aug
17
Sep
7Oct
19 Jul
29 Jun
9Jun
B
Table 3 Parameters of the primary and secondary moult estimated for Common Snipe with the UZ moult models, and the estimated daily rate of
the feather material growth (FMG/day), calculated from the moult durations
a Secondary moult parameters should be considered very approximate due to the non-linearity of PSFMG values over time (Fig.2B)
Flight feathers Mean start date (SE) Duration in days
(SE) Mean end date (SE) SD of the start date
(SE) FMG/day (%)
Primaries 28 Jun (1.6) 53 (2.1) 20 Aug (1.4) 10.2 (0.4) 1.89
Secondariesa29 Jul (1.1) 44 (1.8) 11 Sep (1.5) 16.4 (0.8) 2.27

Journal of Ornithology
maximum value being 14), due to most secondaries being
shed at once and growing at the same time when primary
moult was close to being completed (Fig.3).
The earliest start of the secondary moult was recorded
when PPFMG was 0.40, but it intensified when PPFMG
reached 0.50, and from that moment the mass of new sec-
ondaries grew rapidly (Fig.4). In most cases, the primary
moult was completed before the secondary replacement was
finished, but the time of completing the replacement of both
groups of flight feathers varied greatly between individuals.
The primary moult was completed when PSFMG was in a
wide range between 0.1 and 1.0, with few individuals finish-
ing the secondary moult just before the end of the primary
moult (Fig.4).
The estimated duration of growth for each of the prima-
ries varied from 11 to 21days, while for secondaries from
8 to 11days (Fig.5, TableS2). The daily growth rates of
primaries revealed a progressive increase from innermost
to outermost feather shown by the steeper growth lines
for the outer primaries than those for the inner primaries
(Fig.5, TableS2). As a result, growth rates of individual
primaries largely varied, being about two times higher in
outermost compared to innermost ones. The daily growth
rates of secondaries except for two outermost were similar
and varied between 1.10 and 1.24 PSFMG/day. Secondaries
grew 1.3–2.7 faster than primaries (TableS2) with multiple
feathers replaced simultaneously (Fig.5). Estimated starting
date of S1 and moult end date of S10 were 31 July and 20
August, respectively, suggesting an overall secondary moult
duration of only 20days (TableS2), which is 24days shorter
than duration given by PPFMG (Table3). This discrepancy
is less pronounced in primary feathers, where the mismatch
is 5days only (Table3, TableS2).
The size of the wing gap was negatively correlated with
the fat score (r = − 0.31, P < 0.001). The greatest gap in wing
area with a median PFFMM larger than 0.48 was noted in
Fig. 3 The number of flight
feathers growing simultaneously
while each of 10 primaries
and 10 secondaries was shed
(moult score = 1) with bar
graphs showing the percentage
of growing primaries (grey) and
secondaries (black). Horizon-
tal bold line—median, grey
rectangle—interquartile range,
vertical line—range
shed primarynumber
Number of flight feathers growingsimultaneously
shed secondarynumber
outerinner oute
ri
nner
13579102468
100
0
50
[%]
13579102468
100
0
50
[%]
0
2
4
6
8
10
12
14
16
0.00.2 0.40.6 0.81.0
0.0
0.2
0.4
0.6
0.8
1.0
Proportion of primaryfeather
mass grown(PPFMG)
Proportion of primarysecondary
feathe rmassgrown (PSF MG)
Fig. 4 The scatterplot of proportions of primary and secondary
feather mass grown in Common Snipe

Journal of Ornithology
birds with fat scores between 0 and 2, whereas in those
with fat scores 3 and higher, the median PFFMM distinctly
decreased (Fig.6).
Discussion
Common snipes staging in the study area originate from
the vast breeding grounds of western Russia. Whereas
those originating from northwestern Russia are much less
numerous, as shown by the distribution of ringing recoveries
(Baumanis 1985; Minias etal. 2010). Thus, we assume that
obtained parameters of primary and secondary moult are
representative of Common Snipe breeding in the vast area
of western Russia, which pass numerously through southern
Belarus and winter in Western Europe. A similar approach
was applied in the analysis of the development of breeding
plumage in the Black-headed Gull Chroicocephalus ridibun-
dus, that winter in vast area of central and northwestern
Europe (Meissner etal. 2024).
In many Common Snipe, the primary moult begins on the
breeding grounds (Glutz von Blotzheim etal. 1977) and that
is why only about 1% of individuals that were captured at the
study site had no indication of moult (i.e., all old flight feath-
ers present). The mean growth rate of flight feathers in the
Common Snipe moulting in the middle Pripyat River Val-
ley is one of the highest documented in waders (TableS3).
Fig. 5 Dates of the start and end
of moult of individual primaries
(P1–P10, solid lines) and sec-
ondaries (S1–S10, dashed lines)
moulted by Common Snipe in
the middle Pripyat River Valley.
The endpoints of lines are at
the relative mass of each flight
feather. The grey area shows the
range of average replacement
times for all secondaries
Relative mass of flight feather[%]
0
2
4
6
8
10
12
14
16
18
P1
P3
P2
P4
P5
P6
P7
P8 P9
P10
0
2
4
6
8
10
12
14
24 Jun
29 Jun
4Jul
9Jul
14 Jul
19 Jul
24 Jul
29 Jul
3Aug
8Aug
13 Aug
18 Aug
23 Aug
Date
S1 S2
S3 S4
S5S10
–
Primaries
Secondaries
01234567
0.0
0.5
1.0
1.5
Fat score
Wing gapsize (PFFMM)
Fig. 6 Wing gap size expressed as a proportion of flight feather mass
missing (PFFMM) in Common Snipes with different fat scores. Hori-
zontal line—median, rectangle—interquartile range, vertical line—
range, dots—outliers

Journal of Ornithology
This rapid feather growth and many flight feathers growing
simultaneously (especially secondary feathers) result in a
very short time duration of the wing moult lasting only about
50days. This minimises the time of reduced flight ability
when birds are exposed to increased predation pressure. In
addition, when the wing gap is the largest, Common Snipe
reduce fat stores, thus lowering their wing load. During
wing moult, flight performance is often seriously impaired
(Hedenström and Sunada 1999; Swaddle etal. 1999) and
birds commonly reduce their body mass to maintain good
flight performance (i.e., Holmgren etal. 1993; Serra etal.
1999; Lind and Jakobsson 2001; Galindo-Espinosa etal.
2013). Birds moulting their flight feathers appear to com-
pensate for the aerodynamic effect of the wing gap by
remoulding the flight muscle and reducing their body mass,
thereby effectively increasing the flight-muscle ratio (Lind
and Jakobsson 2001). Moreover, in the Common Snipe, the
moult of greater upper wing coverts is finished before the
secondaries are shed and underwing coverts stay unmoulted
before the moult of secondaries has been completed. It has
been suggested that greater coverts aid flight ability to some
extent by reducing the size of the wing gap (OAG Münster
1975). A similar rapid moult of flight feathers was found in
the Long-billed Dowitcher Limnodromus scolopaceus exhib-
iting the moult migration on its staging area in the Great
Basin (Barbaree etal. 2016). The process of rapid moult
requires extra food available, in the amount above the needs
of daily maintenance (Murphy and King 1992; Lindström
etal. 1993; Bairlein 2017). The middle Pripyat River Valley
provides snipes with abundant invertebrates in wet riverine
meadows (Hajdamowicz etal. 2015; Witkowska etal. 2022).
The pattern of secondary moult in the Common Snipe
resembles that found in species that moult all flight feathers
simultaneously, temporarily losing the ability to fly (Panek
and Majewski 1990; Fox etal. 2014). The extraordinary
rapid replacement of secondaries in the Common Snipe
has been described previously (OAG Münster 1975) where
in most cases, as in our study, shortly before or after the
outermost secondary had finished growing nearly all other
secondaries were shed at the same time. Failure to meet the
assumptions concerning the linearity of the moult model has
consequences in significant difference, i.e., 24days, in the
moult duration of secondaries calculated in the analysis of
individual feathers’ moult (Fig.5) and PSFMG (Table3).
This discrepancy is distinctly lower in the moult of primary
feathers, where the mismatch is 5days only. Difference in
the moult duration estimated by these two methods was as
high as 38days in a study of curlew sandpipers Calidris fer-
ruginea moulting primaries in India (Barshep etal. 2013),
where also the assumption of model linearity was not fully
met (see Fig.1 in this publication). Therefore, when the
increase in the proportion of feather mass over time is not
linear, it is better to use the parameters of UZ moult model
calculated for individual feathers to estimate the duration of
replacement of a given feather tract.
In the Purple Sandpiper, Calidris maritima secondaries are
also shed rapidly, but sequentially from the outermost to inner-
most feather (Summers etal. 2004). Among all wader species
that moult studied with the UZ moult models, this species is the
only one to show higher mean growth rates of primaries than
the Common Snipe (TableS3). The wing moult of the Purple
Sandpiper, especially in the Norwegian wintering population,
seems to occur under time pressure, as these birds finish pri-
mary replacement in early November when weather conditions
become increasingly bad. Completion of wing moult in Com-
mon Snipe in the middle Pripyat River Valley coincides with a
rapid decrease in bird numbers at the beginning of September
(authors’ unpublished data). A drop in the number of Common
Snipe in stopover sites in Poland was reported at a similar time
(Bocheński etal. 2006; Grzywaczewski etal. 2009; Meissner
etal. 2009; Kaczorowski and Czyż 2013). In Western Europe,
this decrease is noted somewhat later, in October (Kraus and
Kraus 1972; OAG Münster 1975; Winkler und Herzig-Straschil
1981; Thies 1996; Laber 2003), which is in line with the south-
west and west directions of autumn movement of this species
across Europe (Baumanis 1985; Minias etal. 2010). Common
snipes complete the post-breeding migration to the wintering
grounds in NW Europe by November/December (Glutz von
Blotzheim etal. 1977), hence, this rapid wing moult enables
them to start to move toward wintering grounds with new flight
feathers. The new feathers provide better flight performance
increasing escape flight speed and energy gain per wingbeat
compared to old feathers (Williams and Swaddle 2003; Heden-
ström 2003). Yet, the distance from the study area to the Com-
mon Snipe wintering grounds is not very large (Minias etal.
2010) and the benefits of having a set of new flight feathers
are unlikely to be significant here. Rapid feather replacement
requires abundant food resources, and this is probably the main
reason for the very high number of Common Snipe staging in
the Middle Pripyat Valley and the very rapid process of flight
feathers replacement.
The size of the wing gap is reduced when subsequent pri-
maries from innermost to outermost are in moult (Holmgren
etal. 1993; Remisiewicz etal. 2009), which was found also
in this study. This is an adaptation to minimize the size of
the wing gap during primary moult because reduced wing
area within outer primaries compromises flight efficiency by
decreasing wing thrust. Whereas during secondary moult,
the gap is much larger due to many feathers shed simultane-
ously. Secondaries are mainly responsible for creating the
lift during flying, and at a time of limited flight capability,
a quick take-off seems to be more important for escaping a
predator than the additional energy cost linked to impair-
ment of a flapping flight, by missing many secondaries. This
is probably the reason for the lower variability in the pro-
gress of primary moult compared to secondary moult.

Journal of Ornithology
The strategy of overlapping moult with migration or breed-
ing seems to be a complex trade-off between environmental
conditions and the time constraints imposed by the time win-
dow for migratory movements (Remisiewicz 2011). As a result,
waders exhibit different moult strategies depending on migra-
tion distance (Holmgren etal. 2001; Meissner and Huzarski
2006), age (Meissner 2007; Summers etal. 2010), sex (OAG
Münster 1991; Summers etal. 2004), and food availability at
the moulting site (Remisiewicz etal. 2009; Barshep etal. 2013).
Our study shows that Common Snipe in the middle Pripyat
River Valley exhibit rapid flight feather moult with large wing
gap and low fat scores, which may suggest that this species
employs moult migration and gather in suitable sites to undergo
the whole process of wing moult before the movement to win-
tering grounds. Moreover, at that time, Common Snipe also
renewed their wing coverts, rectrices, tertials, and most body
feathers (OAG Münster 1975). The moult migration is quite
common in ducks (Salomonsen 1968; Jehl Jr 1990), but there
are only few wader species that combine elements of moult
migration and staging at a single locality (Jehl Jr 1990). In our
study, only 17 individuals (3.2%) were caught more than once
during the season despite the high number of Common Snipe
staging in the study area. The low number of recaptures may
be because birds often avoid areas where they have been cap-
tured previously (Keyes and Grue 1982; Muraoka and Wich-
mann 2007). Yet, it may also indicate that large concentrations
of moulting Common Snipe are only short-term and that the
birds move between the sites where food abundance is high, like
moulting Wood Sandpipers Tringa glareola in South African
inland (Remisiewicz etal. 2009). Hence, it remains unknown
whether moult migration regularly occurs in this species, but
it seems that B-strategy with late and slow movement towards
wintering grounds, allows Common Snipe to moult rapidly at
the early stage of autumn migration and continue migratory
flight with new flight feathers. Large summer and autumn
aggregations of this species in the middle Pripyat River Val-
ley are exceptional (Glutz von Blotzheim etal. 1977). Such
concentrations of thousands of snipes have been recorded only
in the areas abundant in food, such as sewage farms and fish-
ponds or dam reservoirs with periodically released water (Kraus
and Kraus 1972; OAG Münster 1975; Kunysz and Hordowski
1992; Janiszewski etal. 1998). Rapid flight feather replace-
ment requires high food abundance (Wilson and Morrison
1981; Remisiewicz 2011) and perhaps this is why the large
concentrations of the Common Snipe are not often observed.
Hence, the described moult process may apply only to such
unique conditions with large bird concentrations while indi-
viduals migrating in small flocks staging in lower quality sites
may moult differently.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s10336- 024- 02171-2.
Acknowledgements We would like to thank all people who took part in
the activities of the Turov ringing station, especially Natalia Karlionova,
Ivan Bogdanovich, Dzmitry Zhurauliou, Evgenia Luchik, Evgeniy
Slizh, Sergey Moroz, and Alexander Zyatikov. Agnieszka Ożarowska
and Marta Witkowska added useful comments to an earlier version of
the manuscript. The studies were part of the scientific program of the
Institute of Zoology of the National Academy of Sciences of Belarus.
Author contributions PP conceived the idea, and organized and per-
formed the field study. WM analysed the data and wrote the manu-
script. All read and approved the final draft of the manuscript.
Funding This study was possible thanks to funding from the National
Academy of Sciences of Belarus, and APB BirdLife Belarus. The pro-
ject "Polesia—Wilderness Without Borders" is part of the Endangered
Landscapes Programme funded by the Arcadia project coordinated by
the Frankfurt Zoological Society, which provided partial support for
some years.
Data and code availability The data and code are available upon
request to the corresponding author.
Declarations
Conflict of interest The authors declare there is no conflict of interest.
Ethical approval All conducted procedures followed Belarussian law.
Consent to participate Not applicable.
Consent for publication Not applicable.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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