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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: p.musil@post.cz

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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