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Long-term changes in numbers and distributionof wintering waterbirds in the Czech Republic,1966–2008Petr Musil a b , Zuzana Musilová a , Roman Fuchs a c & Simona Poláková a ca Department of Zoology, Faculty of Science, Charles University, Vinicna 7, CZ-128 44 Praha2, Czech Republicb Department of Ecology, Faculty of Environmental Sciences, Czech University of LifeSciences, Kamycka 129, CZ-165 21 Prague 6, Czech Republicc Department of Zoology, Faculty of Science, University of South Bohemia in CeskeBudejovice, Branisovska 31, CZ-370 05 Ceske Budejovice, Czech RepublicPublished online: 09 Aug 2011.
To cite this article: Petr Musil , Zuzana Musilová , Roman Fuchs & Simona Poláková (2011) Long-term changes innumbers and distribution of wintering waterbirds in the Czech Republic, 1966–2008, Bird Study, 58:4, 450-460, DOI:10.1080/00063657.2011.603289
To link to this article: http://dx.doi.org/10.1080/00063657.2011.603289
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Long-term changes in numbers and distributionof wintering waterbirds in the Czech Republic,1966–2008
PETR MUSIL1,2∗, ZUZANA MUSILOVA1, ROMAN FUCHS1,3 and SIMONA POLAKOVA1,3
1Department of Zoology, Faculty of Science, Charles University, Vinicna 7, CZ-128 44 Praha 2, Czech Republic;2Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences, Kamycka 129,
CZ-165 21 Prague 6, Czech Republic and 3Department of Zoology, Faculty of Science, University of SouthBohemia in Ceske Budejovice, Branisovska 31, CZ-370 05 Ceske Budejovice, Czech Republic
Capsule Of 26 species of wintering waterbirds, 18 showed an increase in numbers, five showed adecrease and two showed no change.Aim To assess long-term trends in the numbers and distribution of the 26 most abundant wintering water-bird species in the Czech Republic.Methods We used International Waterbird Census data from between 48 and 639 wetland sites whichhad been counted annually in the Czech Republic from 1966 to 2008. From these data long-term changesin numbers and distributions were determined. Log-linear Poisson regression analysis was used to estimatemissing data using TRIM software. The distribution of each species was described as the ratio of the number ofsites occupied by that species to the total number of sites investigated.Results Increasing trends were found for 18 species, five species were found to be declining, one specieswas stable and two species were found with uncertain trends. Wintering distributions (the ratio of sites occu-pied by a given species to the total number of sites counted) increased in 16 species and decreased in twospecies, broadly correlated with the species changes in numbers.Conclusion In most species changes in numbers as well as changes in distribution followed the WesternPalearctic population trends. Those species which increased were mainly piscivores and included geese,ducks and gulls. Scarcer species also exhibited an increase in numbers. The changes in numbers (both posi-tive and negative) were more frequent among species associated with running water, whereas specieswhich showed uncertain trends were more frequently recorded on standing water, which is more affectedby variable weather conditions.
Trends in many waterbird species, including species of
conservation concern, have changed significantly in
recent decades (e.g. Birdlife International 2004, Wet-
lands International 2006). As in many bird groups, the
population dynamics of waterbird species are affected
by various factors occurring throughout the year, includ-
ing the breeding season, spring and autumn migration,
and the wintering season. Waterbirds generally breed
in low densities over large areas (Scott & Rose 1996,
Kear 2005) but aggregate in large numbers in winter,
when limited availability of suitable habitats may cause
large temporal and spatial variability (Ridgill & Fox
1990). Inter-seasonal variation in numbers and distri-
bution of particular species are considerably affected by
weather and habitat changes (Wahl & Sudfeldt 2005,
Maclean et al. 2008, Musil et al. 2008a, Musilova et al.2009). Changes in wintering conditions can be
assumed as one of the key factors affecting wintering
numbers, over-wintering survival, and consequently
the population dynamics of a particular species.
Among wintering waterbirds in Europe, significant
population trends (either increases or decreases) have
been found in roughly half of all populations (48%; Wet-
lands International 2006), while the remaining popu-
lations are considered as stable, or with uncertain
trends. Although counting effort and coverage of∗Correspondence author. Email: [email protected]
Bird Study (2011) 58, 450–460
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particular countries by monitoring programmes should
be taken into consideration, it still remains remarkable
that, of all the continents, Europe has the highest pro-
portion of populations displaying marked increasing or
decreasing trends (e.g. Kear 2005, Wetlands Inter-
national 2006). Various analyses of wintering waterbird
trends at a national (Crowe et al. 2008, Nilsson 2008,
Slabeyova et al. 2008, 2009, Fouque et al. 2009, Hustings
et al. 2009) or regional (Maclean et al. 2008) level have
been carried out. Nevertheless, there are few studies of
the status of wintering waterbirds in central Europe.
The Czech Republic is not a major waterbird winter-
ing area because the frost period is somewhat prolonged
compared with more western areas of Europe (Hudec
1994, Delany et al. 1999, Musil et al. 2001, Gilissen
et al. 2002). Despite this, the climate is relatively mild
and there is a high diversity of smaller wetland habitats,
which provide some feeding opportunities throughout
the winter period for birds which breed in northern
Europe, particularly when freezing conditions in the
Baltic region may limit the birds’ access to feeding
areas (e.g. Svazas et al. 2001, Nilsson 2008). Conversely,
species with a more southerly distribution, which usually
leave central Europe to winter in Mediterranean areas
(Musil et al. 2001, Cepak et al. 2008), may delay their
southbound movement in milder winters when unfrozen
wetlands are available. The Czech Republic can there-
fore provide attractive wintering areas for waterbird
species with differing wintering strategies (Hudec 1994,
Hudec et al. 1995). To date, there are published analyses
of trends in wintering numbers available only for geese
(Musil et al. 2008a) and ducks (Musilova et al. 2009).
The long tradition of wintering waterbird monitoring
in the Czech Republic started with contributions to the
International Waterbird Census in 1966 and now covers
almost all sites of national importance. We use these
data to try to answer the following questions:
. Do numbers of Czech wintering waterbirds show
long-term changes?. Are the changes in numbers and distribution among
individual waterbird species correlated?. What species-specific variables are responsible for
changes in numbers and distribution of individual
species? We tested the effect of the following
species-specific variables: body size, Western Palearc-
tic population size and trend, mean wintering
numbers and distribution in the Czech Republic, bio-
geographic position, and conservation status at the
national and European level. If global trends are
more important that local conditions, we would
expect that trends in numbers of wintering waterbirds
would follow those in the Western Palearctic. We
predicted that wintering numbers and distribution
would increase particularly in rare and southern
species, due to the northward shift in wintering
range (see Reif et al. 2008). On the contrary, we
expected a decrease in numbers or in distribution of
more northern species, i.e. whose main wintering
range is located in the Baltic. Moreover, we expected
that the protection of individual bird species would
have an effect on their population trend (see
Vorısek et al. 2008). We also expected significant
increase in numbers in huntable species with larger
body size, which were affected by intensive hunting
before the 1970s, but which has since declined (see
Mooij 2005).. Are there any differences in trends in the numbers of
birds which exploit running or standing water? We
expected more conspicuous changes amongst species
on standing water compared to running water,
because standing water is more affected by global
warming that can increase the extent of non-freezing
water bodies suitable for wintering waterbirds.
METHODS
Waterbird data
Long-term trends in the numbers and distribution of
waterbird species were analysed using count data
recorded in the Czech Republic for the International
Waterbird Census (IWC), which is conducted in mid-
January each winter. Within the Czech Republic, the
IWC counts have been carried out annually at
between 48 and 639 wetland sites in January of each
year between 1966 and 2008 inclusive. The IWC
counts were carried out at between 48 and 200 wetlands
sites between January 1966 and 2003. There was a sig-
nificant increase in the number of sites counted
between January 2004 and 2008. In total, between 479
and 639 sites were counted annually in January 2004–
2008. Regional coverage of the Czech Republic
(Fig. 1) as well as the percentage of sites classified as
running and standing waters remained similar in all
the sites from 1966 to 2008 (Fiala 1980, Musil et al.2001, Musilova & Musil 2006). Altogether, 175
wetland sites in the Czech Republic were counted in at
least 10 seasons from the 1960s until 2008 (Musil &
Musilova 2010).
Data for the 26 most abundant waterbird species were
included in the analysis. These species were included in
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the analysis if their annual counts exceeded 50 individ-
uals in any year and if they were recorded in more than
20 winter seasons (see Table 1 for list of species, their
scientific names, distribution, and recent numbers).
The three gull species Larus argentatus, L. cachinnansand L. michahellis were termed ‘large gulls’ and thereafter
considered in the text as only one bird species, in accord-
ance with the taxonomic situation current at the begin-
ning of the study period (i.e. in 1966). The proportion of
missing counts varied between 52.85% and 79.32% and
the proportion of estimated numbers (calculated using
TRIM software: Pannekoek & Van Strien 2005) varied
between 27.87% and 85.21% in particular species.
Thus, the proportion of missing and imputed counts in
any species did not exceed a level of 90%, which can
be regarded as an extremely high proportion of
imputed counts (Soldaat et al. 2007). Wintering
numbers, i.e. numbers of individuals recorded by mid-
winter IWC counts, were used to provide the range of
individuals counted in 2004–2008.
Trend analysis
Trend analyses were carried out using IWC data from
838 of the 1078 sites that were counted in at least two
winters between 1966 and 2008. Log-linear PoissonFigure 1. Distribution of counted sites in the Czech Republic.
Table 1. Number of occupied sites, proportion of missing counts, and estimated numbers in the whole study period (between 1966 and 2008),and estimation of recent wintering numbers in January 2004–2008 (see Methods/Waterbird data for explanation of terms). Data for 26 of themost abundant waterbird species are shown.
Common name Scientific name
Proportion ofoccupied sites
% (n)Proportion of
missing counts %
Proportion ofestimated
numbers %Wintering numbers
2004–2008 (individuals)
Little Grebe Tachybaptus ruficollis 40.2 (337) 68.3 74.6 330–900Great Crested Grebe Podiceps cristatus 14.9 (125) 58.2 68.7 40–320Great Cormorant Phalacrocorax carbo 44.6 (374) 70.9 38.3 9000–14 200Great White Egret Egretta alba 17.7 (148) 70.5 41.6 100–500Grey Heron Ardea cinerea 77.5 (649) 74.7 61.7 1900–2900Mute Swan Cygnus olor 62.7 (525) 72.1 60.6 2000–3800Bean Goose Anser fabalis 9.6 (80) 59.0 85.2 400–6000White-fronted Goose Anser albifrons 5.3 (44) 56.3 84.6 1500–13 800Greylag Goose Anser anser 9.9 (83) 59.1 77.2 800–2400Eurasian Wigeon Anas penelope 10.3 (86) 60.5 58.2 70–170Gadwall Anas strepera 9.2 (77) 60.9 39.7 50–300Common Teal Anas crecca 28.9 (242) 64.0 66.9 450–1200Mallard Anas platyrhynchos 95.0 (796) 77.2 67.6 140 000–180 000Common Pochard Aythya ferina 29.8 (250) 61.8 35.9 800–1400Tufted Duck Aythya fuligula 32.5 (272) 66.7 27.9 3600–5100Common Goldeneye Bucephala clangula 26.1 (219) 60.6 59.3 500–1200Smew Mergellus albelus 8.8 (74) 52.9 61.0 40–110Goosander Mergus merganser 36.0 (302) 67.6 62.1 1500–3300White-tailed Eagle Haliaeetus albicilla 16.2 (136) 65.2 64.9 70–100Common Moorhen Gallinula chloropus 32.5 (272) 65.7 61.2 300–700Common Coot Fulica atra 53.7 (450) 69.8 60.1 8500–11 000Black headed Gull Larus ridibundus 33.1 (277) 64.0 54.6 4000–10 000Mew (Common) Gull Larus canus 14.7 (123) 55.4 68.8 1000–4000Large gulls Larus spp. 21.2 (178) 59.8 39.1 960–2200Common Kingfisher Alcedo atthis 42.1 (353) 72.3 71.6 150–350White-throated Dipper Cinclus cinclus 23.6 (198) 79.3 83.1 330–500
452 P. Musil et al.
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regression analysis was used to estimate missing
data using TRIM software (Statistic Netherlands version
3.52, Pannekoek & Van Strien 2005). Missing data
resulted from incomplete coverage caused by limited
availability of volunteers in some seasons. Serial
correlations between annual numbers and over-
dispersion in the data were taken into account. The
models included change points to allow for changes in
the slope parameters at some points in the time series
(Pannekoek & Van Strien 2005, Fouque et al. 2007,
2009).
The multiplicative slope (i.e. the change in indices
from one year to the next) was the value used to
express population trends over the study period.
Moreover, the TRIM classification of the species trends
was used in one of six categories, depending on
whether the rate of change over the study period was
more or less than 5% per year: a strong increase or
decrease (. 5% per year), a moderate increase or
decrease (, 5% per year), a stable trend (the trend is
not significant and the confidence limits were suffi-
ciently small), or an uncertain trend with large values
of confidence interval (Pannekoek & van Strien 2005,
Fouque et al. 2009).
Additionally, wetlands were classified as standing
water (403 sites: fishponds, reservoirs, gravel and
sand-pit lakes, and industrial settling ponds) or
running water (435 sites: rivers and streams), and
separate trend analyses (using the TRIM software) were
undertaken for each type. For running water (rivers
and streams), sites were defined as river sections with
known boundaries, such as dams, weirs and
bridges (for the list of wetland habitats in Czech
Republic, see Chytil et al. 1999). Percentages of
running and standing waters among counted sites and
regional coverage of the Czech Republic did not
change during the period covered (Musil & Musilova
2010).
Distribution of species
The distribution of each species was described as the
ratio (arcsin transformed) of the number of sites occu-
pied by that species to the total number of sites investi-
gated. Linear regression analysis was then used to
identify potentially significant long-term changes in
species distribution. Correlation coefficients derived
from the linear regression analysis were used to describe
the change in species distribution over the study period
for each species (Table 2).
Species-specific variables
We used the following species-specific variables to find
ecological factors responsible for analysed changes in
numbers and distribution of individual species.
. Six eco-taxonomic groups were used: fish-eating
birds, geese, dabbling ducks, diving ducks, gulls, and
others (see Snow & Perrins 1998).. Mean body weight was used as a measure of body size
(from Snow & Perrins 1998).. Population trends in the Western Palearctic, and
midpoints of population range in the Western
Palearctic, were obtained from Wetlands Inter-
national (2006). Moreover, estimation of breeding
population size and trends in breeding population
(Birdlife International 2004) were used for White-
tailed Eagle, Common Kingfisher, and White-
throated Dipper, whose data are not included in
Waterbird Population Estimates (Wetlands Inter-
national 2006). These three species are breeding as
well as wintering in Europe (Snow & Perrins 1998)
and therefore total population size and population
trends were used from breeding population data
(Birdlife International 2004). We expected similar
trends in wintering as well as breeding numbers of
these species.. The geographical distribution of a species was classi-
fied using the latitudinal midpoint (Lemoine et al.2007), i.e. the mean of the southernmost and north-
ernmost latitudes of the species breeding range (Snow
& Perrins 1998).. Mean numbers and mean distribution for the Czech
Republic were obtained from the Czech IWC data
containing values from the period 1966–2008 (this
study).. The conservation status of a particular species was
classified using its listing in Annex 1 of the EU Bird
Directive (European level) and using the classifi-
cation of the species under Czech legislation Act
No. 114/92 Coll. and Regulation No. 395/1992
Coll., Annex No. III (list of Specially Protected
Animals; Hudec et al. 1999).
Statistical analyses
Effects of species-specific variables on individual species
trends in numbers, and changes in distribution, were
tested by forward selection generalized linear models
(GLM) for normal distribution with the identity link
function in R software (http://www.r-project.org/). Nine
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predictors entered the models but the final solution
included only the best, confined combination of them.
Continuous variables were included as a linear (i.e.
mean body mass) as well as squared terms (i.e. mean
body mass2) predictors; however, no squared variable
was significant. Analysis of independent contrasts were
made. Therefore, in the results, there is one ‘missing’
group in more than two-group variables. This group is
considered as a ‘baseline’ for comparison with other
groups; it means that the significances in tables omit
the difference toward the baseline group.
RESULTS
Trend in numbers and distribution across all sites
Population trends were recorded for 26 common winter-
ing waterbird species in the Czech Republic between
1966 and 2008 (Table 1). Among those investigated,
18 species were found to be increasing and only five
species were recorded as decreasing. The trend of one
species was assessed as ‘stable’ and the trends of two
species were assessed as ‘uncertain’ (Table 2). Distri-
bution (i.e. the ratio of occupied sites to total number
of investigated sites) increased in 16 species and
decreased in only two species. No significant changes
in distribution were found in eight species during the
study period (Table 2).
A significant increase in numbers and range were
found in Great Cormorants, Great White Egrets, Grey
Herons, Mute Swans, White-fronted Geese, Greylag
Geese, Eurasian Wigeons, Mallards, Tufted Ducks, Goo-
sanders, White-tailed Eagles, Common Gulls, ‘large
gulls’ and Common Kingfishers. On the other hand,
declines were recorded in Little Grebes and Common
Teals. There were significant declines in abundance of
Great Crested Grebes, Common Moorhens and
Common Coots, although their distribution range
remained stable. Moreover, an increase in numbers was
recorded in Common Pochards, Common Goldeneyes,
Smews and White-throated Dippers, although their dis-
tribution range remained stable. On the other hand, no
Table 2. Changes in distribution (correlation coefficient (r) and significance: ∗ P , 0.05, ∗∗ P , 0.01, n.s. ¼ not significant; n ¼ 43; seeMethods) and changes in numbers in waterbird species, 1966–2008 (multiplicative rate of change + se) on all wetlands, running and standingwater. The trend categories provided by TRIM software are: SI ¼ strong increase; MI ¼ moderate increase; U ¼ uncertain; MD ¼ moderatedecline; S ¼ stable.
SpeciesChanges indistribution
Changes in numbersAll wetlands Running water Standing water
Little Grebe –0.367 ∗ 0.973 + 0.002 MD 0.974 + 0.002 MD 0.961 + 0.009 MDGreat Crested Grebe 0.182 n.s. 0.982 + 0.006 MD 0.949 + 0.010 MD 1.009 + 0.012 SGreat Cormorant 0.842 ∗∗ 1.172 + 0.009 SI 1.194 + 0.013 SI 1.109 + 0.011 SIGreat White Egret 0.778 ∗∗ 1.262 + 0.064 SI 1.251 + 0.048 SI 1.268 + 0.172 UGrey Heron 0.916 ∗ 1.045 + 0.002 MI 1.046 + 0.003 MI 1.043 + 0.004 MIMute Swan 0.734 ∗ 1.018 + 0.002 MI 1.019 + 0.003 MI 1.013 + 0.004 MIBean Goose 0.476 ∗ 1.022 + 0.015 U 1.063 + 0.018 MI 1.011 + 0.034 UWhite-fronted Goose 0.691 ∗∗ 1.114 + 0.016 SI 1.157 + 0.043 SI 1.081 + 0.215 UGreylag Goose 0.554 ∗∗ 1.160 + 0.018 SI 1.357 + 0.284 U 1.139 + 0.024 SIEurasian Wigeon 0.726 ∗∗ 1.061 + 0.011 MI 1.062 + 0.014 MI 1.047 +0.023 MIGadwall 0.619 ∗∗ 1.163 + 0.132 U 1.052 + 0.017 MI 1.321 + 1.401 UCommon Teal –0.319 ∗ 0.974 + 0.003 MD 0.957 + 0.004 MD 1.005 + 0.008 SMallard 0.576 ∗∗ 1.008 + 0.001 MI 1.004 + 0.001 MI 1.014 + 0.003 MICommon Pochard 0.276 n.s. 1.031 + 0.006 MI 1.045 + 0.008 MI 0.965 + 0.012 MDTufted Duck 0.685 ∗∗ 1.092 + 0.006 SI 1.100 + 0.008 SI 1.011 + 0.008 SCommon Goldeneye 0.181 n.s. 1.016 + 0.003 MI 1.017 + 0.003 MI 0.995 + 0.007 SSmew 0.236 n.s. 1.057 + 0.009 MI 1.056 + 0.011 MI 1.053 + 0.029 UGoosander 0.672 ∗ 1.021 + 0.003 MI 1.019 + 0.004 MI 1.030 + 0.007 MIWhite-tailed Eagle 0.874 ∗∗ 1.088 + 0.007 SI 1.084 + 0.012 SI 1.088 + 0.009 SICommon Moorhen –0.202 n.s. 0.995 + 0.003 MD 0.996 + 0.003 MD 0.953 + 0.008 SCommon Coot 0.013 n.s. 0.992 + 0.002 MD 0.993 + 0.002 MD 0.964 + 0.006 MDBlack headed Gull –0.251 n.s. 0.996 + 0.003 S 0.999 + 0.003 S 0.973 + 0.008 MDMew (Common) Gull 0.336 ∗ 1.052 + 0.006 MI 1.061 + 0.008 MI 1.048 + 0.011 MIlarge gulls 0.826 ∗∗ 1.197 + 0.014 SI 1.277 + 0.169 U 1.187 + 0.019 SICommon Kingfisher 0.544 ∗∗ 1.043 + 0.004 MI 1.041 + 0.004 MI 1.057 + 0.013 MIWhite-throated Dipper 0.096 n.s. 1.013 + 0.003 MI 1.012 + 0.003 MI 1.052 + 0.031 U
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trend (i.e. ‘uncertain trend’) in numbers was found in
Bean Geese and Gadwalls, whose wintering range sig-
nificantly increased. The only ‘stable’ species, without
significant change in either numbers or distribution,
were Black-headed Gulls (Table 2).
Changes in numbers (indicated by the multiplicative
rate of change of values) generally correlated with
changes in distribution (correlation coefficient) (Spear-
man Rank Correlation: rs ¼ 0.777, n ¼ 26, P , 0.0001;
Fig. 2).
Changes in number of waterbirds on standingand running waters
Population trends of wintering waterbirds were analysed
separately for two main wetland habitats, standing and
running waters. Overall, nine increasing, four decreas-
ing, and five stable species were found on standing
water, and 18 increasing, four decreasing, and one
stable species were recorded on running water. Trends
in numbers of individual species in running and standing
water were consistent with the overall trends for all
species (Table 2, Fig. 3). Exceptions were shown only
on standing water and included Great Crested Grebes,
Common Teals, Tufted Ducks, Common Goldeneyes
and Common Moorhens, whose trends were stable,
and Common Pochards and Black-headed Gulls,
whose trends on standing water declined (Table 2).
The number of species with an uncertain trend was
higher on standing water (6) than on running water
(2) (Table 2). The species with uncertain trends
include those which use one of the habitats only margin-
ally (e.g. White-throated Dippers on standing water and
Greylag Geese on running water). Therefore, we
restricted comparison of changes in numbers on standing
and running waters to 18 species with increasing,
decreasing, or stable trends in both habitats. We found
that multiplicative rate of changes in numbers in both
habitats were generally correlated among the waterbird
species analysed (Spearman Rank Correlation: rs ¼
0.716, n ¼ 18, P , 0.001; Fig. 3).
Effect of species-specific variables
Effects of species-specific variables on trends in wintering
waterbirds numbers and on changes in their distribution
were analysed by forward selection GLMs.
Changes in numbers reflect trends in the Western
Palearctic in increasing species but not in decreasing
ones. Moreover, changes in numbers were significantly
higher in rare species which occupy a fewer wetland
sites (Table 3).
Significant differences in changes in distribution
among eco-taxonomic groups were found. An increase
took place among fish-eating birds, geese, dabbling and
diving ducks, and gulls (Figs. 4a,b). Decreases in distri-
bution were more significant in species which have
been decreasing in the whole of the Western Palearctic
(Figs. 5a,b). Conservation status in the Czech Republic
was also correlated with changes in distribution:
increases in distribution were more frequent in non-
protected species. Surprisingly, conservation status at
Figure 3. Relationship between changes in numbers (multiplicativerate of change) on standing and running waters. Only 18 specieswith increasing, decreasing, or stable trends in both habitats areincluded.
Figure 2. Relationship between changes in distribution (correlationcoefficient describing trend in the ratio of the number of sites occupiedto sites counted) and changes in numbers (multiplicative rate ofchange).
Trends in wintering waterbirds in Czechia 455
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the European level (listing in Annex 1 of the EU Bird
Directive) was not correlated with changes in the
numbers and distribution of particular species. Moreover,
the wintering distribution (mean number of occupied sites
in the Czech Republic), wintering numbers (mean
numbers), body size, and geographical distribution of
the species (latitudinal midpoint of the breeding range)
was not correlated significantly with a species trend in
numbers or changes in distribution (Table 3 & 4).
DISCUSSION
Numbers and distribution of most common wintering
waterbird species changed significantly in the Czech
Republic between 1966 and 2008. The proportion
Figure 4. (a) Changes in numbers (multiplicative rate of change)among waterbird groups. (b) Changes in distribution (correlationcoefficient describing trends in the ratio of the number of sites occu-pied to sites counted) among waterbird groups.
Table 3. The forward selection general linear model for changes innumbers (multiplicative rate of change) of bird species in allinvestigated wetlands (F ¼ 3,718 on 5 and 20 DF, P ¼ 0.015). Themodel explains 35.22 % of variability in the data set. For all variablesentered in the analysis see Methods, species-specific variables.
Estimate se t-value P
Intercept 1.095 0.025 43.122 ,0.000Western Palearctic
population trendIncreasing 0.095 0.033 2.905 0.008Decreasing –0.035 0.033 –1.071 0.297Wintering numbers in
Czechia0.000 0.000 1.930 0.068
Wintering distribution inCzechia
–0.002 0.001 –2.740 0.013
Body size 0.000 0.000 –1.642 0.116
Figure 5. (a) Relationships between changes in numbers (multipli-cative rate of change) in the Czech Republic and changes in numbersin the Western Palearctic (Wetlands International 2006). (b) Relation-ships between changes in distribution (correlation coefficient describ-ing trend in the ratio of the number of sites occupied to sites counted)in the Czech Republic and changes in numbers in the WesternPalearctic (Wetlands International 2006).
456 P. Musil et al.
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(88%) of waterbird species whose trends in abundance
were significant seems to be higher than in Europe as a
whole, where changing (decreasing and increasing)
waterbird populations represented 48% of all the
species populations recorded (Wetlands International
2006). Although changes in numbers and distribution
of particular waterbird species in the Czech Republic
often follow the trends in the European populations,
increasing trends are more frequent (18 out of 26
species) in this country. Trends in abundance were
shown to be correlated to, and possibly affected by, the
status of that particular species in the Western Palearc-
tic, and they were also affected by the suitable wintering
conditions in the Czech Republic.
In comparison to general European trends (Wetlands
International 2006), changes in waterbird wintering
numbers in the Czech Republic can probably be
explained by a northward shift in the wintering range
of many species, due to climatic changes (Ridgill &
Fox 1990, Keller 2006, Maclean et al. 2008, Musil
et al. 2008a). However, a comparison of population
trends between countries is limited by differences in
trend period, species included and methods used. More-
over, we can omit species whose distribution is related
(especially in the wintering period) to coastal habitats
(for example, most waders (shorebirds), seaducks and
several goose species), as these occur only in low
numbers in inland European countries such as the
Czech Republic. Comparable trend analyses covering
more than 10 waterbird species are available from, for
example: Slovakia (1991–2006, Slabeyova et al. 2008,
2009); Sweden (1967–2006, Nilsson 2008); Ireland
(1994–2004, Crowe et al. 2008); the UK (1966–2009,
Calbrade et al. 2010); the Netherlands (1976–2008,
Hustings et al. 2009); France (1987–2008, Fouque
et al. 2009); Bulgaria (1977–2001, Michev & Profirov
2003). Despite methodological differences, we can
compare the proportion of species with increasing,
decreasing, or no (i.e. stable, uncertain, unknown, fluc-
tuating) trends. In most of these countries (Sweden,
Czech Republic, Slovakia, UK, the Netherlands and
Bulgaria), the number of increasing species was higher
than the number of decreasing species. However,
increasing species were in the majority among all inves-
tigated species only in Sweden (13 of 17 species, Nilsson
2008), France (12 of 17 species, Fouque et al. 2009), the
Netherlands (16 of 28 comparable species, Hustings et al.2009) and the Czech Republic (18 of 26 species, i.e. this
study). Decreasing species were in the majority only in
the Irish study (Crowe et al. 2008). Surprisingly, increas-
ing species were more dominant among investigated
species than decreasing ones in other western European
countries (see above). Some slight north–south
differences can be also seen by comparing the Czech
data (69% of increasing species) with Slovakia, where
only 41% of species were increasing in wintering
numbers.
In general, the changes in numbers and distribution of
waterbird species in the Czech Republic were consistent
with species population trends in the Western Palearc-
tic. However, differences in trends between the Czech
Republic and the numbers along recognized flyways
were shown for some species. Numbers and distribution
of Common Teals have declined significantly in the
Czech Republic, whereas this species has increased in
other European countries (see for example, Wahl &
Sudlfeldt 2005, Fouque et al. 2009, Calbrade et al.2010). The decrease of Common Teals in the Czech
Republic may be related to the negative impact of inten-
sive fishpond management (see, for example, Musil et al.2001, Musil 2006), which has affected the breeding,
migrating and also the wintering numbers of this
species. On the other hand, the numbers of three
species (Bean Geese, Common Pochards and Mew
(Common) Gulls) have decreased in the Western
Palearctic flyway (Wetlands International 2006),
whereas their numbers and/or distribution have
increased in the Czech Republic. Among these species,
Common Pochards and Mew Gulls have expanded
their breeding and wintering range, not only in the
Czech Republic but also in other central European
Table 4. The forward selection general linear model for changes indistribution (correlation coefficient between arcsin-transformed ratioof occupied size and year) of bird species in all investigated wetlands(F ¼ 5.199 on 9 and 16 DF, P ¼ 0.002). The model explained 60.19% of variability in the data set. For all variables entered the analysissee Methods, species-specific variables.
Estimate se t-value P
Intercept –0.078 0.132 –0.595 0.561Western Palearctic
population trendIncreasing –0.147 0.156 –0.940 0.361Decreasing –0.487 0.165 –2.946 0.009Body size 0.000 0.000 1.266 0.224Eco-taxonomic groups
Fish-eating birds 1.129 0.187 6.049 ,0.001Geese 0.720 0.194 3.717 0.002Dabbling ducks 0.647 0.177 3.655 0.002Diving ducks 0.594 0.175 3.396 0.004Gulls 0.728 0.235 3.096 0.001
Species protection (Czechlegislation)
–0.340 0.136 –2.502 0.024
Trends in wintering waterbirds in Czechia 457
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countries (e.g. Slovakia, Slabeyova et al. 2008). The
increasing distribution of Bean Geese in the Czech
Republic may be related to a shift in wintering sites
within Europe (Madsen et al. 1999, Wetlands Inter-
national 2006, Fox et al. 2010). Nevertheless, the
trend in the wintering numbers of this species has been
classified as ‘uncertain’, due to its fluctuations in relation
to varying mid-winter temperature (Musil et al. 2008a).
Mallards are another interesting species whose numbers
and distribution have increased in the Czech Republic,
whereas there has been a decrease in wintering
numbers reported from northwest and northeast
Germany (Wahl & Sudlfeldt 2005), Slovakia (Sla-
beyova et al. 2008, 2009) and also from Ireland
(Crowe et al. 2008) and the UK (Calbrade et al.2010). Numbers of Mallards have been affected by the
long-term releasing of this species for hunting purposes
in the Czech Republic, especially since 1990 (Musil
et al. 2001). Between 2003 and 2007, numbers of
released Mallards reached 150 000–220 000 individuals
(unpubl. data).
Changes in numbers generally correlated with changes
in distribution. Nevertheless, the magnitude of the
increase in the range of some species (for example,
Grey Herons, Eurasian Wigeons, Mallards, Goosanders
and White-tailed Eagles) was high compared with
other species, indicating that they had the highest rate
of expansion over the study period. These species seem
to have become more widespread, as opposed to being
concentrated in relatively few sites. On the other
hand, Great Crested Grebes, Common Moorhens and
Common Coots are decreasing species which do not
exhibit significant changes in distribution.
Running water (streams, rivers) and standing water
(including fish ponds, reservoirs, gravel and sand-pit
lakes, and industrial settling ponds) represent the two
main categories of wetland habitats (Chytil et al.1999) available for wintering birds in the Czech Repub-
lic. Although the changes in numbers in these two
habitat types were generally consistent among the water-
bird species analysed, there were noticeable differences
in changes in numbers related to habitat. Species with
a highly significant trend (increasing or decreasing) in
numbers throughout the entire Czech Republic
changed their numbers similarly in both habitat types.
In six species, we found differences in trends on standing
and running waters which can be related to the habitat
preferences of the species (Hudec 1994, Snow &
Perrins 1998, Delany et al. 1999, Musil et al. 2001,
2008b, Gilissen et al. 2002). Among these species,
numbers of diving ducks (Common Pochards, Tufted
Ducks, Common Goldeneyes) increased on rivers and
conversely were found to be decreasing or stable on
standing water. Those species probably avoid inten-
sively-managed fish ponds affected by the intensive
grazing effect of Carp Cyprinus carpio stocks (Musil
et al. 2001). Nevertheless, an increase in the importance
of non-freezing standing water for other species (e.g.
Great White Egrets, Greylag Geese, Gadwalls, Mallards,
large gulls) can be expected in the coming years, in
accordance with the global climate change forecasts
which predict milder winters across Europe, including
the Czech Republic (Huntley et al. 2007, IPCC 2007).
The changes in wintering numbers and distribution of
particular species were affected by many species-specific
variables. Among these, species trends in the Western
Palearctic (Birdlife International 2004, Wetlands Inter-
national 2006) were the most significant. Amongst the
various eco-taxonomic groups, the most remarkable
increases in numbers and distribution were shown by
the fish-eating birds, followed by the geese, dabbling
ducks and gulls. This pattern of change is similar to
the published data for population changes in Europe as
a whole (Wetlands International 2006, Birdlife Inter-
national 2004).
We found that the rate of change in distribution was
lower in species protected under Czech conservation
law. These species were listed as specially protected
because of their long-term decline in numbers (Musil
et al. 2001). However, negative trends shown in these
species (e.g. Little Grebes and Common Teals) were
not reversed by protection measures imposed under
Czech conservation law. Changes in the size of the
breeding population of 189 bird species were analysed
using data from Atlases of Breeding Distribution in the
Czech Republic (St’astny et al. 2006) between 1985
and 1989 and between 2001 and 2003. Although
increasing trends are prevailing among specially pro-
tected species, their population trends have not been
reversed since the law providing for their conservation
at the national level. Increase in numbers continued in
species which were increasing before the adoption of
conservation laws. Likewise, species which were decreas-
ing before this adoption continued to decrease (Vorısek
et al. 2008).
Finally, we found that the trends in wintering numbers
were negatively correlated with wintering distributions,
i.e. number of occupied wetlands. This phenomenon
can be explained by the northwards expansion of winter-
ing waterbirds in central Europe, similar to the changes
recorded in western or northern Europe (Maclean et al.2008, Nilsson 2008), or anticipated for breeding
458 P. Musil et al.
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populations in most of Europe (Huntley et al. 2007), in
response to the expected climatic changes (IPCC 2007).
Nevertheless, decrease in wintering distances, as well as
shift of range were found to be more significant in terres-
trial than wetland bird species (cf. Reif et al. 2008, Visser
et al. 2009). Although the effect of climatic changes on
numbers and distribution of bird species are often dis-
cussed in many papers, relevant studies analysing this
phenomenon seem to be scarce.
ACKNOWLEDGEMENTS
We are very grateful to all the volunteers who were involved
in waterbird counts and also to the census co-ordinators of
the International Waterbird Census (IWC) in the Czech
Republic (Bohuslav Urbanek, Vladimır Fiala, Cestmir Folk,
Josef Kren, Ivana Kozena, Jitka Pellantova). IWC in the
Czech Republic was organized in cooperation with the
Czech Society for Ornithology. We are also grateful to Steve
Ridgill and Lucie Fuchsova for language improvement. We
thank Tony Fox (NERI, Denmark) for useful comments to
earlier versions of the manuscript and Leo Soldaat (Centraal
Bureau voor de Statistiek, The Netherlands) for useful
advice on trend analysis. We are also grateful to anonymous
referees for useful comments which helped to improve our
manuscript.
This study was supported by the Ministry of Environment of
the Czech Republic, Project VaV MZP CR SP/2d3/109/07
entitled ‘The long-term changes in numbers and distribution
of waterbirds in the Czech Republic in relation to climatic
and environmental changes’.
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