The occurrence of Knot Calidris canutus outside
the breeding season is restricted to soft-sediment
intertidal areas, where it mainly feeds on small
molluscs. Red Knots C. canutus canutus appear
only during autumn migration towards African
wintering grounds in the Baltic region (Meissner
2005a). This species undertakes long-distance
flights between the arctic breeding grounds and
temperate or tropical wintering areas (Piersma &
Davidson 1992), and for fast refuelling it needs to
stop in sites with high densities of benthic inverte-
brates (Piersma et al. 1992). The sandy coasts of
the southern Baltic represent a low quality habitat
for migrating Knots, where the birds might
encounter difficulties to find sufficient food to
meet energy demands. Bivalves, which are the
main prey of Knot outside the breeding period, are
inaccessible for most of the time due to a lack of
regular tides. Even when the water level drops
during periods of strong wind and the bottom in
shallowest places is exposed, the density of mol-
luscs within reach of the waders is much lower
than in the Dutch Wadden Sea (Piersma et al.
1993, Kube 1994, Górecki 2003, Wlodarczak-
Komosi´nska 2004). Moreover, feeding conditions
for waders on the Baltic coasts are very change-
able and unpredictable due to variable water level
(Kube 1994, Wlodarczak-Komosi´nska 2004).
Stopover strategy of adult and juvenile Red Knots
Calidris c. canutus in the Puck Bay, southern Baltic
Meissner W. 2007. Stopover strategy of adult and juvenile Red Knots
Calidris c. canutus in the Puck Bay, southern Baltic. Ardea 95(12):
For Red Knots Calidris c. canutus sandy coasts of the southern Baltic
seem to be a low quality stopover site, because of unpredictable feeding
conditions and a low density of molluscs. Observation collected in the
Puck Bay, Poland, suggest that Knots feed mainly on Nereis sp.,
Gammarus sp., small sized Hydrobia sp. and small insects taken from
wet sand. Among 1471 Knots ringed 27.8% of juveniles and 10.5% of
adults were retrapped few days after the first capture, which indicates
that the majority had a short stay and apparently departed with small
energetic reserves. In spite of poor feeding conditions the fuel deposi-
tion rate of the Knots in autumn (adults: 2.4 g per d, juveniles: 2.7 g per
d) was similar to that observed in the Dutch Wadden Sea and the Baltic
coast of SE Sweden. It is suggested that Knots are able to accumulate
body stores despite low food quality and density because the lack of
tides allow them to forage without interruption, and because there is no
additional energetic cost related to increasing gizzard size.
Key words: Knot, southern Baltic, autumn migration, stopover strategy
Avian Ecophysiology Unit, Department of Vertebrate Ecology &
Zoology, University of Gda´nsk, Al. Legionów 9, 80-441 Gda´nsk, Poland;
ARDEA 95(1), 2007
Additionally, invertebrates in the brackish water of
the Baltic are smaller than their congeners in inter-
tidal areas of the North Atlantic (Kautsky 1998).
Furthermore, there is a strong competition from
other waders, especially Dunlin Calidris alpina and
Curlew Sandpiper Calidris ferruginea, which are
numerous on the Baltic coasts at the same time. In
mixed flocks Knots lose the majority of interspe-
cific aggressive interactions even with smaller
waders (Stawarczyk 1984).
The irregular occurrence of adult Knots and
their very low body mass (Meissner 2005a,
Meissner & Kamont 2005) indicate that the south-
ern Baltic is rather an emergency feeding place,
than a regular stopover site on the route from
Siberia to Africa. The mean body mass of adult
Knots caught in autumn in the southern Baltic is
among the lowest reported for the subspecies C. c.
canutus (Piersma et al. 1992, Meissner & Kamont
2005). Autumn records of juvenile Knots in the
southern Baltic are dispersed along the migration
route, and are less concentrated than adults at tra-
ditional stopover sites (Gromadzka 1992, Diersch-
ke 1995). Thus, it is possible that juveniles migrate
in small hops rather than in long-distance flights,
as adults do, using the southern Baltic as one of
many stopover sites along their migration route. If
true, it might be expected that adults and juveniles
behave differently in use of stopover sites.
The aim of this paper is to compare the
stopover pattern of adult and juvenile Knots at the
Polish Baltic coast in autumn, on their way
towards the wintering grounds. Particular focus is
on key features of stopover strategies, i.e. the
length of stay and body mass changes.
Studies were conducted between 1988 and 1995
in the western part of the Gulf of Gda´nsk (Puck
Bay), on the narrow sandy spit in Rewa village
(Fig. 1). The length of the spit depended on water
level and varied from c. 500 to 1000 m. Waders
were caught and ringed on a regular basis, using
walk-in traps (Meissner 1998). Fieldwork lasted
from mid-July through the end of September. This
period covered almost the whole period of Knot
migration in the study area (Meissner & Sikora
1995). In total, 1071 juvenile and 400 adult Knots
were ringed. Each Knot was aged (Prater et al.
1977) and weighed with an accuracy of 1 g.
Lengths were measured of wing, total head, bill
and tarsus (Meissner 2000). To estimate energy
reserves, it was necessary to correct for body size
because the size of adults and juveniles decreased
progressively through the season (Meissner &
Kamont 2005). Among the measurements taken,
the wing length in adults and total head length in
juveniles showed the highest correlation coeffi-
cient with body mass (r=0.32 and r=0.33,
respectively, both P< 0.05). However, wing length
might vary within the season due to abrasion of
GULF OF GDA ´
Location of the ringing site at Rewa (RE) and
other places mentioned in the text: RM = Reda mouth,
VM = Vistula mouth.
Meissner: STOPOVER STRATEGY OF KNOTS
the longest primary (Pienkowski & Minton 1973),
potentially affected by food quality during the
moult (Pehrsson 1987). Therefore, both in juve-
niles and adults the total head length was used to
correct body mass (correlation coefficient between
total head length and body mass in adults r=
0.29, P< 0.05). The adjusted body mass of each
bird was calculated from the residuals of the
regressions of body mass on total head length for
juveniles and adults.
Body mass changes were expressed as the dif-
ference between body mass at the first and subse-
quent captures. To obtain an instantaneous mea-
sure of the rate of body mass increase birds
trapped within four days after first capture were
selected. The length of stay was estimated using
capture–recapture techniques following Schaub et
Along the coast of the Puck Bay only few sites
are suitable for waders to feed. The most impor-
tant ones are close to the river mouths of the
Vistula and Reda (where the main study area was
located). Within the study period, waders were
also ringed at the mouth of the Vistula river
(about 45 km apart in a straight line) (Gromadzka
1998). Some birds used only a single area, while
others were recorded in both regions. During
autumn migration the majority of wader move-
ments within Puck Bay were directed from the
eastern to the western part (Brewka et al. 1987).
To show the intensity of passages of Knots within
the Puck Bay, the Index of Direct Recoveries (IDR)
between two ringing sites was calculated (Busse
1982). It was deduced from the number of recov-
eries per 100 birds ringed at one site and 100 birds
caught at the second as:
IDR = V
=number of birds ringed at the ring-
ing site 1 and recovered within the same season at
ringing site 2, NR
=number of ringed birds at
site 1, NC
=number of caught birds at site 2
(including retraps and recoveries). All other statis-
tical methods followed Zar (1996). Analyses were
done in STATISTICA 6.0 software (StatSoft 2001).
Number of retraps and length of stay
In total 298 (27.8%) juveniles were retrapped
within the same autumn, and only 42 (10.5%)
adults (comparing the percentages, χ
P<0.0001). The mean length of stay of adults
(2.98 days) was about three times shorter than in
juveniles (9.36 days).
Body mass changes
Two-way ANOVA indicated significant differences
in mean adjusted body mass among years (F
=6.15, P<0.0001), but not age (F
P=0.86) and not year-age interaction (F
0.83, P=0.56; Fig. 2).
During the first four days after capture, juve-
niles exhibited a similar body mass increase
among years (ANOVA, F
The number of retraps of adults was much lower
and comparing two years with a reasonable sam-
ple size (1991 and 1995, when ten and eleven
retraps occurred) indicated no year effect (t-test,
P>0.05). Thus, within each age class samples
from all years were combined for subsequent
Knots from both age classes increased body
mass significantly during their stay (Fig. 3).
body mass (g)
1990 1992 1994
1989 1991 1993 1995
Changes in the adjusted body mass in adult and
juvenile Knots caught in consecutive seasons. Indicated
are mean, SD (box), range (whiskers) and sample size.
ARDEA 95(1), 2007
Juveniles that were retrapped had a lower body
mass at first capture than birds caught only once.
There was no such difference in adults (Fig. 3).
There were large differences among individuals
in body mass increment. Some juveniles gained
more than 60 g after 10 days, while others hardly
changed their body mass after this period (Fig. 4).
The overall body mass increase during the first
four days was similar in adults (mean 2.4 g day
±3.70 SD, n=38) and juveniles (mean=2.7 g
±4.13 SD, n=223; t-test, t=0.39, P=
0.70). However, adults did not stay as long as
juveniles and their body mass at last capture was
on average about 7 g lower than that of juveniles
(Cochran-Cox test, t'=3.55, P=0.0007; Fig. 3).
Juveniles which lost body mass during the first
day after catching had a significantly higher
adjusted body mass than birds that put on mass
from the beginning onwards (Fig. 5) (t-test, t=
3.20, P=0.002). Small sample sizes of retrapped
adults did not allow a similar comparison,
although the few data indicate a similar pattern as
in juveniles; three adults which lost body mass
body mass (g)
no retr retr 2
no retr retr 2
Comparison of mean body mass of Knots caught
only once (No retr) and in retraps at the first (Retr 1) and
the last capture (Retr 2) in adults (ANOVA, F2,325 = 3.76,
P= 0.002) and in juveniles (ANOVA, F2,1294 = 56.27, P<
0.0001). Arrows indicate significant difference according
to post-hoc Tukey test at P<0.05. Indicated are mean,
SD (box), range (whiskers) and sample size.
body mass (g)
body mass decreasing
Mean adjusted body mass at first capture in
juveniles increasing (dark grey) and loosing (light grey)
weight after one day. Indicated are mean, SD (box), range
(whiskers) and sample size.
body mass (g)
10 122468 20
14 16 18
body mass (g)
Changes in the body mass in following days bet-
ween first and subsequent capture of adult and juvenile
Knots retrapped in Rewa.
Meissner: STOPOVER STRATEGY OF KNOTS
during the first day after capture, weighed 112 g,
119 g and 134 g, which was much higher than the
mean adjusted body mass of adults that increased
their weight after one day (mean 101.0 ± 12.27
Between 1988 and 1995 movements of 16 juve-
niles and 4 adults between Vistula and Rewa were
recorded. In juveniles the period between ringing
at Vistula and recapture in Rewa ranged between
0 and 33 days (median 3). Five of them (31%)
were retrapped after two days. In adults, three
birds were recorded the same day at both sites,
while the fourth was recorded at the second site
after three days. The Index of Direct Recoveries
between Vistula and Rewa was noticeably higher
in adults (IDR = 0.67) than in juveniles (IDR =
0.29). In the opposite direction only one juvenile
bird moved (IDR = 0.02).
Of the Knots ringed at Rewa, several were
recovered at a distance of more than 100 km; 24
juveniles and 6 adults. This indicates recovery
rates of 2.2% and 1.5%, respectively, which are
not significantly different (χ
0.37). Among these recoveries, six juveniles and
one adult were retrapped in the western Baltic at
the Langenwerder Island (450 km in a straight line
from the study area) no later than after 9 days
(one juvenile after 21 days), while other records
came from the intertidal area of the North Sea and
Fuel deposition rates of adult Red Knots in the
Puck Bay were similar to those observed in
autumn in the Dutch Wadden Sea (2.8 g d
in the Baltic coast of SE Sweden (2.7 g d
lated for both age classes) (Nebel et al. 2000,
Helseth et al. 2005). However, in the Wadden Sea
Knots stay much longer than in the Baltic area and
the departure body mass of adult females is esti-
mated at about 200g (Nebel et al. 2000). During
their stay at the southern Baltic coasts Knots spend
most of their time on foraging (Dierschke & Rippe
1997, own observations), similar to other Calidris
species (Górecki 2003, Wlodarczak-Komosi´nska
2004). They are able to accumulate fat stores
despite low food quality and density because the
lack of tides makes long periods of foraging with-
out interruption possible. Another reason that
Knots achieve a similar fuelling rate on poor qual-
ity Baltic sandy coasts as in rich intertidal mudflats
might be the gizzard size, which in Knots varies
considerably during the year (Dekinga et al. 2001,
van Gils et al. 2005). After the breeding season the
gizzard of Knots increases rapidly in response to a
shift in diet from rather soft-bodied arthropods to
hard-shelled molluscs (Dekinga et al. 2001, van
Gils et al. 2005). These adjustments of digestive
organs are important for permitting the high feed-
ing rate during migration and wintering (van Gils
et al. 2003, 2005). However, a large gizzard
entails higher maintenance and transport cost and
hence overall energetic costs increase with gizzard
size (Piersma et al. 2003, van Gils et al. 2003).
There are no empirical data on the gizzard size of
Knots from Baltic stopover sites, but it is likely that
birds arrive there directly from the breeding
grounds (Meissner 2005a). Thus, when landing in
the southern Baltic area, both adults and juveniles
might still have a small stomach to increase later
in tidal areas when the birds change diet to hard-
shelled molluscs (Dekinga et al. 2001, Battley &
Piersma 2005). This assumption is in agreement
with data on small stomachs of Knots arriving in
autumn in the Dutch Wadden Sea and islandica
Knots making stopover in Iceland after leaving
their breeding grounds (Battley & Piersma 2005).
Data on stomach contents of two Knots obtained
by stomach pumping in 2001 and observations of
foraging birds also strongly suggest that they feed
on the same prey as Dunlins in this area, e.g.
Nereis sp., Gammarus sp., small sized Hydrobia sp.
and different small insects taken from wet sand
(A. Wlodarczak-Komosi´nska, unpubl. data).
The percentage of retraps was lower and the
mean length of stay was shorter in adults than in
juveniles, and similar differences were found in
other wader species in Puck Bay during autumn
ARDEA 95(1), 2007
migration (Meissner & Koziróg 2001, Meissner &
Sciborski 2002, Meissner 2005b, Meissner &
Górecki 2006). The very low number of retraps
(Meissner 1992, this study) indicates that the
majority of Knots probably departed with small
energetic reserves after a short stay. However,
some juvenile birds (especially those with small
energetic reserves at arrival) stopped for few days
and they were able to achieve a considerable gain
of weight. Thus, body mass at departure varied,
being larger in birds after some days of refuelling.
The decision to depart immediately or to stay and
gain body mass must be taken individually accord-
ing to information gathered from the environment.
Weather conditions might be an additional factor
which strongly influences the stopover time
(Alerstam 1979, Weber & Hedenström 2000).
However, in the period of Knot autumn migration,
weather conditions along the southern Baltic coast
are usually favourable for birds flying in western
direction and there are only few days with strong
head winds at low altitudes making westward
flight impossible (Remisiewicz 1996).
Adults and juveniles that stop at the non-tidal
areas of the southern Baltic were recorded later in
tidal areas of Western Europe (Gromadzka 1992),
and the recovery rate of Knots ringed in the Puck
Bay is higher than in many other wader species
(Meissner & Remisiewicz 1998). Thus, it seems
that Knots cope with poor feeding conditions at a
low quality stopover site, yet accumulate sufficient
energetic reserves for further migration. It is possi-
ble that the lack of additional energetic costs
related to a large gizzard is one of the reasons of
the high refuelling rate in Knots feeding on low
quality food on the southern Baltic sandy coasts.
Despite of a longer period of stay, juveniles
seemed to search for better feeding places less
often than adults. One of the reasons might be
that juveniles lack previous experience consider-
ing high profits of foraging on molluscs and about
the relative richness of tidal mudflats of the
This study was conducted by the Waterbird Research
Group KULING (paper no. 125). Jaga Gromadzka kindly
provided data on the number of ringed and caught Knots
in the Vistula mouth. We are grateful to all colleagues
from WRG KULING and to many volunteers who helped
in collecting the data in the field. Special thanks to Anna
Wlodarczak-Komosi´nska, who provided data on prey of
Knots and to Robert Krupa and Maciej Kozakiewicz who
spent many days in Rewa creating unforgettable atmos-
phere of this ringing station. And final thanks to
Magdalena Remisiewicz for help in preparation of this
paper and to two anonymous referees for helpful com-
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ARDEA 95(1), 2007
Voor Kanoeten Calidris c. canutus op najaarstrek lijkt het
zuiden van de Oostzee op het eerste gezicht een matig
tussenstopgebied. De zandige kust herbergt amper
schelpdieren en de voedselomstandigheden zijn onvoor-
spelbaar vanwege de windrichting en windkracht, die de
waterstand en daarmee de mogelijkheid om voedsel te
zoeken bepalen. Om te onderzoeken of deze onvoorspel-
bare voedselomstandigheden een weerslag hebben op de
snelheid waarmee Kanoeten lichaamsreserves aanleggen,
werden vogels gevangen en gewogen in de Puck Baai in
Polen. In dit gebied aten Kanoeten vooral Zeeduizend-
poot Nereis sp., Vlokreeft Gammarus sp., Wadslakje
Hydrobia sp. en kleine insecten die ze van het zand
oppikten. Er werden aanzienlijk meer jonge (1071) dan
oude vogels (410) gevangen. Op basis van terugvangsten
in hetzelfde seizoen werd geschat dat de verblijfsduur
van jonge vogels 9,4 dagen bedroeg, van oude vogels
slechts 3,0 dagen. Het kwam als een verrassing dat de
gewichtstoename per dag (adulte vogels 2,4 g, jonge
vogels 2,7 g) vergelijkbaar was met de toename in de
Nederlandse Waddenzee en de Oostzeekust van ZO-
Zweden. Er wordt verondersteld dat het lage voedselaan-
bod gecompenseerd wordt door het ontbreken van getij
waardoor de vogels permanent kunnen eten. Ook zou het
ontbreken van de noodzaak de maag te vergroten, zoals
schelpeters dat doen, een extra energetisch voordeel kun-
nen opleveren. (JP)
Corresponding editor: Jouke Prop
Received 30 June 2006; accepted 16 March 2007