Hydrobiologia 279/280: 511-519, 1994.J. J. Kerekes (ed.), Aquatic Birds in the Trophic Web of Lakes. 511© 1994 Kluwer Academic Publishers. Printed in Belgium.

Changes in abundance of water birds species in southern Bohemia(Czech Republic) in the last 10 years

Petr Musil & Roman Fuchs 2Institute of Applied Ecology, Agricultural University of Prague, Kostelec nad Cernymi lesy, CZ-218 63;

2South Bohemian University, Faculty of Biology, Branisovsk6 31, Ceske Budkjovice, CZ-370 05, CzechRepublic

Key words: fishponds, waterfowl, Anatinae, Podicipediformes, Fulica atra, Galinulla chloropus, Larusridibundus, Phalacrocorax carbo, Cygnus olor, and Anser anser

Abstract

In 1981-1992, the breeding fauna of 153 fishponds was studies in three fishpond regions in southBohemia (Czechoslovakia). On each pond, all water and wetland birds were censused by the Two-checkmethod, which consists of adult birds counts during each breeding season (the first in the second partof May, and the second in the second part of June). We assessed the numbers of all species living inwater and wetland habitats in the breeding season.

The decline in abundances (expressed as number of individuals) of ducks (Anatinae), grebes(Podicipediformes), Coot (Fulica atra), Moorhen (Galinulla chloropus), Black-headed Gull (Larusridibundus) were the most marked changes recorded. Marked increase in abundances was found inCormorant (Phalacrocorax carbo) and Mute Swan (Cygnus olor) during the whole decade, whereas inGraylag Goose (Anser anser) the increase was restricted to the first half of the period under study.Numbers of charadriform and passeriform birds fluctuated in the dependence of water level variation.

Introduction

The fishponds and pond systems currently exist-ing in Czech Republic are the result of landscapemodification by numerous generations of its in-habitants. Fishponds have been created in suit-able places chiefly in Bohemia and Moravia sincethe 13th century. Intensive development of fish-pond management took place mainly during the15th and 16th centuries. Fish production was themajor purpose of creating fishponds. Of course,fishpond management led to the development ofshallow and eutrophic water bodies, often over-grown with littoral macrophytes and thus createdsuitable areas for breeding, resting or migratingwaterfowl.

The attention of ornithologists has concen-trated on the bird fauna of fishponds since thelate 1890s (see e.g. Capek, 1890; Mrazek &Zdobnitzky, 1943). However, more numerouspapers on the quantitative composition of birdfauna inhabiting fishponds did not appear untilthe 1960s, 1970s and 1980s (Havlin, 1967;Hudec, 1975; epa, 1987; Fiala, 1987). Apartfrom these, many other investigations refer notonly to the quantitative and qualitative composi-tion of breeding birds communities on our fish-ponds, and to requirements of particular species,but also to short and long-term trends in birdnumbers.

The attention of ornithologists has been fo-cused upon changes in numbers of several water

512

an wetland birds because marked changes ob-served in particular aquatic and marshland birdspecies that have been breeding on Czech fish-ponds since the early 20th century (e.g. Cernk,Hudec, 1977; Stastny et al., 1987).

A dramatic change in water birds numberswas noted in the early 1980s. The breedingnumbers of the most abundant duck species andsome other waterfowl, which has been increasingfor several decades, began to decline abruptlyin many fishpond regions (Fiala, 1987; Repa,1987). This declines are different from any otherchanges in abundances of terrestrial bird species.Our investigations were initiated then in order toobtain missing data, determine the range of thesedeclines, and find possible explanations reveal.

Study area

In 1981-82, 1986-87, and 1991 the breedingpopulations of aquatic birds were censused in 158fishponds of total area 44,86 km2 (Table 1) ofthese fishponds, 123 lie in the Tiebofi Basin Bio-sphere Reserve, which is one of the largest, old-est and best known fishpond districts of CzechRepublic. Twenty one ponds are located in asmaller fishpond region about 20 km north of theTiebofi Basin in the vicinity of the town of Kar-dasova Re6ice. The remaining 14 ponds are lo-cated in a relatively isolated minor fishpond areaabout 60 km north of the latter (in the surround-ings of the town of Sedl6any).

Methods

During the first two research periods (1981-82and 1986-87) a subset of ponds were studiedduring the first year, and the remainder during thesecond year. In 1991, all ponds were censusedduring the one breeding season.

In all ponds under study two checks were car-ried out during each breeding season, one of themin the second part of May, and the other onein the second part of June (Musil, Fuchs, 1991).On each check all adult birds of the speciesunder study were counted during walking aroundeach pond. We assessed numbers of all speciesof Podicipediformes, Pelecaniformes, Ciconii-formes, Anseriformes, Ralliformes, Charadrii-formes, Lariformes; Alcedo atthis and those spe-cies of raptors and Passeriformess which live inaquatic and marsh habitats (see Table 2 for thecomplete list of the species considerated).

In the case of bird species that are difficult todetect or that exhibit territorial behaviour (e.g.passeriform and ralliform birds, some certaincharadriiform species) each record of territorialor breeding behaviour was considered to repre-sent the observation of two individuals of therespective species.

Two sets of abundance values were obtainedfor each species under study on each pond. In thecase of secluded or territorial species (Tachybap-tus ruficollis, Botaurus stellaris, Ixobrychus minu-tus, Anser anser, Circus aeruginosus, Rallidae,Charadriiformes, Passeriformes) the higher value

Table 1. Summary characteristics of 158 fishponds under study in 1981-1991.

Fishpond characteristic Minimum - maximum (average)

Total area (km2) 0.0017 - 3.9494 (0.2970)Water surface area (km2) 0.0012 - 3.4000 (0.2559)Littoral stands area (km2) 0.0003 - 0.5494 (0.0412)Ratio littoral stands area/total area (%) 0.86 - 69.90 (21.80)Length of circumference of water surface (km) 0.16 - 12.34 (1.84)Mean water depth (m) 0.0 - 2.6 (0.66)Elevation (a.s.l.) (m) 412.0 - 494.0 (441.88)

513

Table 2. Changes in abundances (expressed as a number of observed individuals) and densities (abundance/km 2) of particularbird species on 158 ponds under study in 1981-82, 1986-87 and 1991.

Species Abundance (n) Density (n/km 2)

81, 82 86, 87 91 81, 82 86, 87 91

Podiceps cristatusPodiceps grisegenaPodiceps auritusPodiceps nigricollisTachybaptus ruficollis

Phalacrocorax carbo

Ardea cinereaArdea purpureaNycticorax nycticoraxIxobrychus minutusBotaurus stellarisCiconia ciconia

Ciconia nigra

5761

550 414

563 226 193282 250 120

3 120 229

4272

191

18

4561

28

263

464

29

79

Cygnus olorAnser anserAnas platyrhynchosAnas streperaAnas penelopeAnas creccaAnas querquedulaAnas acutaAnas clypeataNetta rufinaAythya ferinaAythya fuligulaAythya nyrocaBucephala clangula

Haliaeetus albicillaCircus aeruginosus

81191

2018661

3944

8126

21565866

1136

33

642

892985

Rallus aquaticus

Porzana porzanaGallinula chloropusFulica atra

141279994502

117

31

3112

9171847

82

260

242

581464

252112

1111807

1.814.26

44.9914.74

318

0.870.98

1935

8941747

271

1.810.58

48.06130.77

0.023.03

49 0.74

48 1.430.041.98

66.5440

1435

3.146.22

22.1611.190.020.380.690.02

24

5.622.50

24.7717.990.000.070.40

0.69 0.420.27 0.780.44 19.931.18 38.95

0.041.83 1.58

0.041.34

0.540.041.29

32.64

1.09

1.07

0.8931.99

Vanellus vanellusCharadrius hiaticulaCharadrius dubius

Calidris alpinaCalidris temminckiiCalidris minutaPhilomachus pugnaxActitis hypoleucosTringa glareola

329

84

38

37

87 25211

29 111

1213

2 63 13

7.33 1.94

1.87

0.070.180.82

0.65

0.040.07

12.840.02

12.556.29

0.07

12.26

5.045.57

2.68

10.170.020.62

0.040.130.07

9.23

0.024.302.68

5.11

10.34

0.65

0.160.20

9.520.040.420.02

0.40

5.620.252.470.020.040.020.070.130.29

514

Table 2. (Continued)

Species Abundance (n)

81, 82

8Tringa ochropusTringa nebulariaTringa erytropus

86, 87 91

2431

Density (n/km2 )

81,82

0.18

86, 87

18Limosa limosaNumenius phaeopusGallinago gallinagoLarus ridibundusLarus minutusChlidonias nigerSterna hirundo

Alcedo atthis

4716132

15116

4

6

108235

17109

51

208710

11546

0.40

1.05359.63

0.332.59

3 0.09

0.13 0.110.02

0.22 0.45183.58 194.17

0.020.38 0.332.43 1.03

0.07

Anthus pratensisMotacilla flavaMotacilla cinereaMotacilla albaLuscinia svecicaSaxicola rubetraLocustella naeviaLocustela filuviatillisLocustella luscinioidesAcrocephalus schoenobaenusAcrocephalus palustrisAcrocephalus scirpaceusAcrocephalus arundinaceusPanurus biarmicusRemiz pendulinusEmberiza schoeniclus

1010

16 9 12215 170 260

366 26 61

34 42 4834 32 2010 16 8

1266 938 972290 554 440

1028 880 122892 84 70

234 146 104

628 437 684

TotalNumber of species

3683252

1994351

2131262

821.1052

444.59 475.1151 63

was considered to represent their abundance (i.e.numbers of individuals) whereas in the remainingspecies an average of both value was used.

Results

General trend in species richness and in totalwaterfowl abundance

Altogether 70 species of water and wetland birdswere found in the studied area. The species rich-

ness in 1991 was considerably higher than speciesrichness in preceding years. Among species newlyrecorded in 1991 waders were predominantly rep-resented. Being obviously late migrants, their oc-currence on studied ponds is presumably a con-sequence of draining of ponds due to harvestingthe fish stock.

Changes in total abundance (e.g. total numbersof individuals) of observed bird species corre-sponded to changes in numbers of main water-fowl group (Lariformes, Anseriformes, Grui-formes, Podicipediformes - see Fig. l a and b).

91

0.540.070.02

0.364.79

0.130.760.760.22

28.226.46

22.922.05

0.7614.00

0.203.79

0.580.940.710.36

20.9112.3519.62

1.87

3.259.74

0.220.220.275.800.801.361.070.450.18

21.679.81

27.381.560.042.32

15.25

515

others

Passeriformes

Lariformes

Gruiformes

Anseriformes

Podicipediformes

Charadriiformes

Falconiformes

Ciconiiformes

Pelecaniformes

yearsFig. 1. A. Changes in total abundances of main waterfowl group. B. Changes in total abundances of rarer waterfowl groups (inFig. 2a marked as others).

-*%j

30-

u).i

I-

20-

u)

'1

._

E

o

10-

0-

.1 ^rn

IL -V

1000-

a

'4-:I-

aEc:

750-

500-

l1~

81-82

86-87years

86-87

91

91

250-

0-

�

,,

---

--

--

--

I J~S 1

m-

m-

---

b------

516

Total abundances of Charadriformes, Passeri-formes and Falconiformes did not correspondedto this trend. The total abundance of Pelecani-formes, represented only by Phalacrocorax carbo,increased markedly during the period understudy.

Changes in abundances of particular water andwetland species

The changes in the numbers of particular aquaticand marshland bird species in our study area inthe course of the 1980s are summarized inTable 2.

Abundances of 4 species (Anas crecca, Anasquerquedula, Anas clypeata, Gallinula chloropus)was declined markedly during the whole 1980s.Abundances of 9 species (Podiceps nigricollis, Anasplatyrhynchos, Aythya ferina, Aythya fuligula, Bu-cephala clangula, Fulica atra, Larus ridibundus, Ac-rocephalus schoenobaenus) declined markedly onlyin the first half of studied period and abundancesof other 5 species (Podiceps cristatus, Tachybaptusruficollis, Sterna hirundo, Locustellafiuviatillis) onlyin the second half of 1980s.

The abundances of 4 species were increasingconsiderably in the course of whole 1980s (Pha-lacrocorax carbo, Saxicola rubetra, Cygnus olor,Ciconia nigra) and abundances of 2 species (Nyc-ticorax nycticorax, Locustella naevia) increasedmarkedly only in the first half of 1980s.

In other species, no marked trends in abun-dance were recorded or, if any, they were foundonly in small numbers of individuals.

Discussion

Ducks, grebes, coots and gulls

The decline in the numbers of all duck species aswell as in many other aquatic bird species (e.g.Podiceps sp., Fulica atra, Gallinula chloropus, Larusridibundus) during the first half of the 1980s isobviously the most important change recorded.Similar decline has been observed in many fish-

pond regions of former Czechoslovakia (Fiala,1987, Repa, 1987). This reduction came to a haltin the second half of the 1980s, and, (Anas strep-era, Netta rufina) abundances of some speciesbegan to increase again. However, the decline inabundances has not been satisfactorily explainedso far.

In many fishpond regions in former Czecho-slovakia, an increasing of mortality was recordedin many aquatic birds (most frequently due tobotulism) between 1975-1983 (Hudec et al.,1984). Similarly, massive loss-rates due to botu-lism were reported from some others central Eu-ropean countries in 1981-83 (Reichholf, 1983,1985). A significant decline in the reproductivecapacity (i.e. clutch size, brood size, numbers ofbreeding pairs and their ratio to the total numbersof duck populations) was observed in most ducksand other waterfowl species in the 1980s (Kloubec& Svecova, 1990; Musil, 1990).

Decreasing abundances of some duck species(Anas platyrhynchos, Anas strepera, Aythya ferina,Aythyafuligula) can be partly explained by gradualcoverage of islets, which are optimal breedinghabitats for a number of duck species (Stastnyet al., 1987b) by shrubs and trees. The decline inabundances of some other duck species (Anascrecca, Anas querquedula, Anas clypeata) can byexplained by draining and ploughing of meadowsadjacent to the fishponds, and by bulldozing thelittoral vegetation (Bejcek et al., 1990), and thusby destruction of their breeding habitats.

Furthermore it is possible to expect a negativeeffect of gradually increasing fish stock size, whichwould result into the competition between fishand some waterfowl, e.g. ducks (Pykal, personalcommunication).

Cormorant

The most marked increase in numbers (seeTable 2) was recorded in Cormorant (Phalacro-corax carbo), which is consistent with an increaseof this species populations within whole Europe(e.g. Cramp & Simmons, 1986; Sellers, 1989;Suter, 1989; Menke, 1989; Aubrecht, 1991, etc.).

517

The first breeding colony rose in our study areas(and also in Bohemia) in 1983 (see Musil et al.,1993 for datail on its development).

Mute Swan & Greylag Goose

Numbers of breeding pairs of both these speciesin south Bohemia was a continually increasing forseveral decades (Hora, 1989; Simek, 1991). Theincrease of Mute Swan (Cygnus olor) abundancecontinued the second half the 1980s (see Table 2),being thus consistent with an expansion of thisspecies in Czech Republic (Stastny et al., 1987,Stastny & Bejcek, 1989; Hora, 1989). Increasingabundance of Greylag Goose (Anser anser) cameto a halt in the half of the 1980s, and then beganto decrease (see Table 2.), which may be presum-ably considered as a consequence of repeated de-watering of many fishponds in breeding season(Simek, 1991).

Waders

The numbers of most waders depend, to a con-siderable extent, on the decrease of water due todewatering of ponds in order to harvest the fishstock. Dewatering ponds are preferred by wadersbreeding on ponds (Vanellus vanellus, Charadriusdubius), on in their vicinity (Tringa ochropus) andalso by spring migrating waders (Actitis hypoleu-cos, Philomachus pugnax, Tringa glareola, andother waders species - see Table 2).

The decline in abundances of waders species,which breed in meadows and wetlands (Tringatotanus, Limosa limosa, Gallinago gallinago), hasbeen continuing already for several decades as aconsequence of the agricultural changes men-tioned above (Salek, 1987; Stastny et al., 1987a).

Passeriformes

The majority of Passeriform birds dependstrongly on littoral stands, i.e. on their breedinghabitats. Hence the are Passeriform birds are

usually negative affected by dewatering of pondsdue to harvesting the fish stock, which might havecoincided with the their breeding season in sev-eral last years. The differences in abundancechanges of particular Passeriform birds, can beexplained by different requirements (e.g. Chatch-pole, 1972; Leisler, 1981) of these species for themagnitude of flooding of littoral stands. The de-crease was therefore recorded in those speciesthat are more dependent on habitats in which themacrophytes are flooded (Acrocephalus schoe-nobaenus, Acrocephalus arundinaceus, Locustellaluscinioides) whereas in those dependent on lit-toral stands only little or not at all (Acrocephalusscirpaceus, Emberiza schoeniclus, Saxicola rubetra,Luscinia svecica) no declines in abundances werefound.

Importance of changes in species abundances in thestudy area

In evaluating the trends of the development ofnumbers of several bird species, the fact must betaken into account that Czech Republic lies at thenorthern limit of the breeding range of some birdspecies (e.g. Ardea purpurea, Nycticorax nyctico-rax, Netta rufina) or, on the contrary, at its south-ern edge (e.g. Aythyafuligula, Bucephala clangula,Tringa ochropus). Consequently, one may expecta greater variation in numbers of breeding pairshere than in the centres of their respective ranges(Cramp & Simmons, 1986, 1987). Furthermore,one should also consider the period fact that evenduring the period of the greatest decline in breed-ing numbers, the densities (see Table 2) of manyspecies in our study areas were many times higherthan those observed in other parts of their respec-tive breeding ranges (see e.g. Kjellen, 1978;Haapanen & Nilsson, 1979; Thomas, 1980;Poysa, 1983; Koskimies & Poysa, 1989).

Conclusion

In 1981-1991, the breeding fauna of 153 fish-ponds was studied in three fishpond regions in

518

south Bohemia (Czech Republic). On each pond,all water and wetland birds were censused by theTwo-check method (Musil & Fuchs, 1991), whichconsists of two adult birds counts during eachbreeding season (one of them in the second partof May, and the other one in the second part ofJune). We assessed the abundances (i.e. numbersof individuals) of all species living in water andwetland habitats in the breeding season.

The decline in abundances (expressed as num-ber of individuals) of ducks (Anatinae), grebes(Podicipediformes), Coot (Fulica atra), Moorhen(Galinulla chloropus), Black-headed Gull (Larusridibundus) were the most marked changesrecorded. Marked increase in abundances wasfound in Cormorant (Phalacrocorax carbo) andMute Swan (Cygnus olor) during the whole de-cade, whereas in Graylag Goose (Anser anser) theincrease was restricted to the first half of the pe-riod under study. Numbers of charadriform andpasseriform birds fluctuated in the dependenceon water level variation.

Acknowledgements

This study could have been conducted to the fieldterrain work of almost 20 ornithologists, whichparticipated on the field census. Our thank arealso due to Dr Joseph J. Kerekes for his kindnessmaking possible to present our results at AquaticBirds Symposium' 1991 in Sackville and to PetrPySek for improving our English.

References

Aubrecht, G., 1991. Historische verbreitung und aktuelleBrutversuche der Kormorans in Osterrreich. Vogelschutzin Osterreich 6: 44-47.

Bej6ek, V., A. Exnerovi, R. Fuchs, P. Musil, L. Simek,K. Stastnr, P. VaSik, 1990. Zmeny po6etnosti jednotlivychdruhfi vodnich ptfkfi na vybranych rybnicich Tfebofisk6panve - srovnani let 1981, 1982 a 1986, 1987. Ptaci vkulturni krajine, Sbornik referatu, Ceske Budejovice: 17-24.

Catchpole, C. K., 1972. A comparative study of territory inthe Reed Warbler (Acrocephalus scirpaceus) and Sedge War-bler (Acrocephalus schoenobaenus). J. Zool., Lond. 166:213-231.

Cramp, S. & K. E. L. Simmons, (Chief editors)., 1986. TheBirds of the Western Palearctic. Vol. I.: Ostrich to Ducks.Oxford University Press.

Cramp, S. & K. E. L. Simmons, (Chief editors)., 1987. TheBirds of the Western Palearctic. Vol. III.: Waders to Guls.Oxford University Press.

Capek, V., 1890. Novitaiten der Local-Ornis von Oslavany inMahren und einige weitere Beobachtungen aus dem Jahre1889. Orn. Jahrbuch 11: 8-13.

CernS, W. & K. Hudec (eds), 1977. Fauna CSSR, Ptaci 2.Academia, Praha.

Fiala, V., 1987. NmiStsk& rybniky 1959-1985 a jejichptactvo. Vlast. sbor. Vysociny, odd. vd prir., 8: 203-237.

Haapanen, A. & L. Nilsson, 1979. Breeding waterfowl popu-lations in northern Fennoscandia. Ornis Scand. 10: 145-219.

Havlin, J., 1967. Birds breeding on the Namitske rybnikyponds. Act. sc. nat. Brno I: 429-471.

Hora, J., 1989. Zakladni informace o populaci labute velkeCygnus olor (Gm.) v Jihoceskem kraji. Ptaci v kulturni kra-jini, Sbornik referti, Ceske Bud6jovice: 87-102.

Hudec, K., 1975. Density and breeding of birds in the reedswamps of southern moravian ponds. Act. sc. nat. Brno 9:1-40.

Hudec, K., J. Pelantovi & V. Rachac 1984. Hromadn6 uhynyvodniho ptactva v CSSR. Vodni ptactvo a jeho ivotniprostfedi v CSSR, Brno: 81-88.

Kjellen, N., 1978. The breeding bird fauna in Lake Immeln,Skane, south Sweden, 1977. Anser 17: 41-48.

Kloubec, B. & Z. Svecova, 1990. Zmeny po6etnosti jiho6esk6populace racka chechtav6ho (Larus ridibundus L.) a jejichmozn6 pri6iny. PtBci v kulturni krajine, Sbornik referatfl,Ceske Budejovice: 119-140.

Koskimies, P. & H. Poysit 1989. Waterfowl censusing in en-vironmental monitoring: a comparison between point andround counts. Ann. Zool. fenn. 26: 201-206.

Leisler, B., 1981. Die okologische Einnischung der mitteleu-ropaischen Rohrsanger (Acrocephalus, Sylviinae). I. Habi-tattrennung. Wogelwarte 31: 45-74.

Menke, T., 1989. Recent population development of the Cor-morant Phalacrocorax carbo sinensis in the Federal Republicof Germany. In M. R. van Eerden & M. Zijstra (eds). Proc.workshop 1989 on Cormorants Phalacrocorax carbo, Rijsk-waterstaat Directorate Flevoland, Lelystad: 49-52.

Mrazek, J. & F. Zdobnitzky, 1943. Die Vogelwelt der Nami-ester Teiche und ihrer Umgebung. Zeitschrift des Mahr.Landesmuseums, N. F. 3: 179-216.

Musil, P., 1990. Changes in abundance and structure ofbreeding populations of ducks in a smaller fishpond regionin the town Kardasova Recice in southern Bohemia. BirdsCensus and Atlas Studies. Proc. XIth Int. Conf. on BirdCensus and Atlas Work., Prague 1990: 441-445.

Musil, P. & R. Fuchs, 1991. Pedbezne souhrnn vsledkyprvych ti let Sitbni hnizdnich populaci hnizdnich popu-laci vodnich ptaku. Zpravy CSO 33: 25-29.

Musil, P., J. Janda & H. de Nie, 1993. Change in abundance

519

and foraging habitat selection in Cormorant Phalacrocoraxcarbo in the south Bohemia (Czech Republic). Ardea 81 (inpress).

Reichholf, J., 1983. Ausbrfiche von Enten-Botulinismus imSommer 1982 in Bayern. Anz. orn. Ges. Bayern 22: 37-56.

Reichholf, J., 1985. Vogelverluste durch Botulismus amInnstausse Egglfing-Obernberg im Sommer 1983. Anz. orn.Ges. Bayern 24: 85-88.

Repa, P., 1987. Anderungen in der Abundanz der nistendenWasservOgel auf den Teichen in der Gelanderfurche Ta-chovski brazda (Sfidwestbohhmen) in den Jahren 1973-1984. Vest. s. zool. spol. 51: 304-317.

Sellers, R. M., 1989. Breeding and wintering status of Cor-morant on the British Islets. In M. R. van Eerden & M. Z-ijstra (eds). Proc. workshop 1989 on Cormorants Phalac-rocorak carbo, Rijskwaterstaat Directorate Flevoland,Lelystad: 30-35.

Sutter, W., 1989. Bestand und Verbreitung in der Schweizfiberwinternder Kormorane Phalacrocorax carbo. Orn.Beob. 86: 25-52.

Salek, M., 1987. K historii a souEasnosti roziifeni bfehouie6ernoocas&ho, Limosa limosa L., a vodouie rudonohbho,Tringa totanus L., v Ceskobudejovicke a Tfebofiske panvi.Avifaunaji2nich Cech ajeji zmeny, Sbornik refertfl, CeskeBudejovice: 119-140.

Simek, L., 1991. Monitoring populace husy velk6 (Anser anse(L.)) na Tfebofisku v letech 1976-1990. Panurus 3: 77-84.

Stastny, K., K. Hudec, A. Randik, 1987. Atlas of breedingdistribution of birds in C.S.S.R. 1973/77. Academia, Praha.

Thomas, G. J., 1980. The ecology of breeding waterfowl at theOuse Washes, England. Wildfowl 31: 73-88.