Acta Zoologica Lituanica, 2001, Volumen 11, Numerus 3

ISSN 1392-1657

235

RECENT CHANGES IN DISTRIBUTION OF WINTERINGPOPULATIONS OF WATERFOWL ESTABLISHED ONTHE BASIS OF LITHUANIAN RINGING RECOVERIES

Saulius ÐVAÞAS1, Rièardas PATAPAVIÈIUS2, Mindaugas DAGYS3

1, 3 � Institute of Ecology, Akademijos 2, 2600 Vilnius, Lithuania2 � Lithuanian Bird Ringing Centre, Museum of Zoology, Laisvës 106, 3000 Kaunas, Lithuania

Abstract. Recent changes in the wintering grounds of the Lithuanian breeding population of MuteSwan, Mallard, Common Pochard, and Coot were established by means of the analysis of the long-termringing data stored in the Data Bank of the Lithuanian Bird Ringing Centre. Significant changes in thewintering grounds of Mute Swan and Mallard of the Lithuanian breeding population have occurredsince the late 1980s; the wintering grounds of Common Pochard and Coot, on the other hand, havechanged just unremarkably. These changes were primarily caused by human impact and an increasednumber of mild winters during the present climatic amelioration.Key words: wintering waterfowl, ringing recoveries, distribution, Lithuania

INTRODUCTION

Study of ringing recoveries has been successfully usedearlier in investigating the impact of cold weather move-ments on wildfowl in Western Europe (Bailie et al.,1984; Ridgill & Fox, 1990). Results of those wide-rangestudies of ringing data showed a close correlation be-tween meteorological conditions and large-scale win-ter movements of wildfowl. The aim of the present studywas to analyse available ringing data in order to estab-lish possible long-term changes in the distribution ofwintering waterbirds of Lithuanian breeding popula-tions.

MATERIAL AND METHODS

All available ringing recoveries, stored in the Data Bankof the Lithuanian Bird Ringing Centre at Kaunas Zoo-logical Museum since 1929, of Mute Swan (Cygnusolor), all duck species (Anas and Aythya spp.), and Coot(Fulica atra) were analysed. For a further investiga-tion, merely the ringing recoveries (including controls,recaptures, sightings, etc.) of 265 Mute Swans, 114Mallards (Anas platyrhynchos), 33 Common Pochards(Aythya ferina), and 119 Coots ringed in Lithuania dur-ing the breeding season and recaptured in winter wereselected (Table 1).Due to the insufficient number of the recoveries it wasdecided that no analysis should be attempted on the

other duck species available in the Data Bank of theLithuanian Bird Ringing Centre. All the ringing recov-ery data were coded in New EURING Codes (1979).The following information was coded for each recov-ered bird: ring number, bird species, ringing date, ring-ing co-ordinates (latitude and longitude degrees andminutes), recovery date, recovery co-ordinates (asabove), recovery circumstances, distance travelled be-tween the ringing place and the recovery place, and otherinformation. Prior to the analysis, the co-ordinates ofthe ringing and finding locations were transformed intodegrees with minutes expressed as a decimal part of adegree, with the western longitude and the southernlatitude expressed as negative numbers. Therefore, allthe co-ordinates in this study are presented in decimaldegrees.Maps plotted for each analysed species show the over-all distribution of the birds ringed in Lithuania duringthe breeding season and recovered in winter and grav-ity points for different time periods. The size-scaledcircles on the maps represent the number of the recov-eries in the squares of one degree of longitude by halfdegree of latitude. The period for which the recoverydata for the birds ringed in Lithuania were availablewas divided into three or four time periods, each con-taining an approximately equal number of recoveries.The co-ordinates of the gravity points for different timeperiods were calculated as the arithmetic means of find-ing the longitudinal and latitudinal co-ordinates of thebirds ringed in Lithuania during the breeding season

236Ðvaþas S., Patapavièius R., Dagys M.

and recovered in winter during those time periods. Themean distances travelled by the birds recovered duringeach of the time periods were calculated, too. To com-pare the mean distances travelled by the birds in subse-quent time periods, t-test was used.

RESULTS

Mute Swan

The mean recovery position of wintering Mute Swanof the Lithuanian breeding population was calculatedfor three subsequent periods (1970�1986, 1987�1991,and 1992�1999). Significant changes in the winteringgrounds of Mute Swan of the Lithuanian populationwere established for the last two periods (Fig. 1).In the 1970s to the early 1980s, the mean recovery po-sition of wintering Mute Swan of the Lithuanian breed-ing population was established in the coastal region ofnorthwest Germany. The average distance between thebreeding sites and the wintering sites was 694 km (Ta-bles 2, 3).During the analysed period the key wintering area ofLithuanian Mute Swan was located in Denmark (over50% of all the recoveries). Numerous swans were re-corded in Germany and the Netherlands, too. Just about20% of all the recoveries were from Poland. In Decem-ber�February of the severe winters of the 1960s�1970s,separate birds were recovered also in the UK, Switzer-land, Italy, and France, the greatest recorded migratoryroute distance making 1,716 km. Significant changesin the gravity points were recorded during subsequentperiods (1987�1991 and 1992�1999). The mean recov-ery position of wintering Mute Swan of the Lithuanianbreeding population was established at the southerncoast of the Kaliningrad Region of Russia. The aver-age calculated distance between the ringing and find-

Table 1. The number of selected recoveries of Mute Swan, Mal-lard, Pochard, and Coot, ringed in Lithuania during the breedingseason and recovered during the winter months.

foyrtnuoCyrevocer

etuMnawS drallaM drahcoP tooC

airtsuA 7 1

suraleB 1 1

muigleB 1 1 3

dnaainsoBanivogezreH

1

airagluB 1

aitaorC 1 2 5

cilbupeRhcezC 4 1

kramneD 17 1 4

dnalniF 1

ecnarF 2 81 71 42

ynamreG 85 74 2 21

eceerG 2

yragnuH 2

dnalerI 2

ylatI 1 2 1 44

aivtaL 3

ainauhtiL 24 01

ainodecaM 2

sdnalrehteNehT 21 8 1 21

dnaloP 96 9 1

aissuR 2

ainevolS 1 1

niapS 2

nedewS 3

dnalreztiwS 1 4

eniarkU 1

modgniKdetinU 1 1 3

aivalsoguY 1

latoT 562 411 33 911

doirepemiT ecnatsidnaeM ES egnaR n t fd P

6891–0791 63.496 06.12 6171–0 481391.01

598.0-

232

97

100.0<

373.01991–7891 83.922 25.63 859–0 05

9991–2991 01.182 27.34 998–0 13

Table 2. Mean distances travelled by Mute Swans ringed during the breeding season in Lithuania and recovered in winter,and t-tests between the means of subsequent time periods.

Table 3. Mean co-ordinates of finding of Mute Swans ringed during the breeding season in Lithuania and recovered in winter.

doirepemiTedutitaL edutignoL

nnaeM ES naeM ES

6891–0791 81.31 33.0 91.45 11.0 481

1991–7891 88.91 36.0 08.45 01.0 05

9991–2991 48.91 87.0 46.45 31.0 13

237Changes in distribution of wintering populations of waterfowl

ing locations were just 230 and 281 km during the sec-ond and third time periods, respectively. The averagemigration distance during the last decades was about413�465 km shorter than that in the 1970s. During thelast two decades the key wintering sites of Mute Swanof the Lithuanian origin were recorded in Lithuania(primarily in the coastal region, the stretch of theNemunas River in Kaunas city , the stretch of the ÐeðupëRiver in Marijampolë city, in Elektrënai reservoir, andin Druskininkai city) and in Poland (the Gulf ofGdansk). More and more of Mute Swans stayed in theirbreeding grounds throughout the year, with over 50%of the recoveries received from Lithuania in the mildwinters of the early 1990s (Þalakevièius et al., 1995).Winter movements of these largely sedentary birds sel-dom exceeded 100 km. It was only in the severe win-ters of 1985�1987 that small numbers of winteringswans were recorded in Denmark, Germany, and theNetherlands, with the greatest recorded migratory routedistance of 1,300 km. Even in the severe winter of 1995�1996 most recoveries were, however, from the south-east Baltic coast (up to 750 km from the breeding sites).In recent years, swans of the Lithuanian origin wererecorded wintering in Ukraine and Central Europeancountries, too, the bulk of the native population stillremaining in the Eastern Baltic region.

Mallard

The mean recovery position of wintering Mallard ofthe Lithuanian breeding population was calculated forfour subsequent periods (1931�1970, 1971�1978,1979�1985, and 1986�1999). Significant changes in thewintering grounds of Mallard were established for thelast decade (Fig. 2). In the 1930s to the early 1980s, themean recovery position of wintering Mallard of theLithuanian breeding population was established in cen-tral Germany. Just very small changes in the mean re-covery position (up to 150 km) occurred during the sub-sequent periods in 1931�1985. The average distancebetween the ringing and finding sites was about 960�1,100 km (Tables 4, 5).During the analysed period the key wintering areas ofMallard were located in Germany and France (over50% of all the recoveries). Numerous ducks were alsorecorded in the Netherlands, Austria, and other West-ern and Central European countries. In severe win-ters, separate wintering birds were recovered also inthe UK, Italy, and Croatia, with the greatest recordedmigratory route distance of 1,841 km. A marked short-ening of the average distance of the migratory routewas recorded beginning with the late 1980s. During1986�1999, the mean recovery position of wintering

Figure 1. Overall distribution of Mute Swan ringed in Lithuania during the breeding season and recovered in winter and thegravity points for the subsequent time periods since 1970.

238Ðvaþas S., Patapavièius R., Dagys M.

Table 4. Mean distances travelled by Mallards ringed during the breeding season in Lithuania and recovered in winter and t-tests between the means of the subsequent time periods.

Table 5. Mean co-ordinates of finding of Mallards ringed during the breeding season in Lithuania and recovered in winter.

doirepemiT ecnatsidnaeM ES egnaR n t fd P

0791–1391 07.7501 19.85 4261–0 72504.0-

914.1

103.2

55

06

55

786.0

161.0

520.0

8791–1791 78.2011 50.27 3281–37 03

5891–9791 61.169 32.96 1481–0 23

9991–6891 82.396 94.79 8551–0 52

doirepemiTedutitaL edutignoL

nnaeM ES naeM ES

0791–1391 09.01 80.1 08.94 75.0 72

8791–1791 15.9 20.1 41.05 64.0 03

5891–9791 16.11 69.0 92.05 93.0 23

9991–6891 74.41 14.1 79.15 26.0 52

Figure 2. Overall distribution of Mallard ringed in Lithuania during the breeding season and recovered in winter and thegravity points for the subsequent time periods since 1931.

Mallard of the Lithuanian breeding population wasestablished at the German-Polish border. During thepast 15 years the average distance between the breed-ing sites and the wintering sites was 693 km and thegravity point of the recoveries shifted about 350 kmnorth-eastwards. In recent years, most recoveries ofwintering Mallard of the Lithuanian origin were re-ceived from Lithuania, Poland, and eastern Germany.

Mallards increasingly remained in their breedinggrounds.In recent years, major part of the Lithuanian Mallardpopulation was partially migratory; at certain sites, theestablishment of largely sedentary sub-populations wasrecorded. Even in severe winters, the greatest recordeddistances between the wintering sites and the breedingsites of Mallard rarely exceeded 1,000 km.

239Changes in distribution of wintering populations of waterfowl

Table 6. Mean distances travelled by Common Pochards ringed during the breeding season in Lithuania and recovered inwinter and t-tests between the means of the subsequent time periods.

doirepemiT ecnatsidnaeM ES egnaR n t fd P

5691–3591 17.1851 99.79 1502–997 71631.0

352.0-

32

41

398.0

208.05791–6691 05.6551 78.471 8691–017 8

9991–6791 83.8161 29.661 5002–047 8

Figure 3. Overall distribution of Common Pochard ringed in Lithuania during the breeding season and recovered in winterand the gravity points for the subsequent time periods since 1953.

Common Pochard

The mean recovery position of wintering CommonPochard of the Lithuanian breeding population wascalculated for three subsequent periods (1953�1965,1966�1975, and 1976�1999).The analysis did not reveal any major changes in thewintering grounds of Common Pochard of the Lithua-nian population over the last 50 years (Fig. 3). In the1950s to the early 1970s, the mean recovery positionof wintering Common Pochard of the Lithuanian breed-ing population was established in northeastern France.The average calculated distance between the breeding

and wintering sites was about 1,570 km (Tables 6, 7).Over 50% of all the recoveries were received fromFrance (especially from the deltas of the Loire and theRhone Rivers). Wintering Common Pochards were alsorecorded in the Netherlands, Ireland, Denmark, andother countries of the North Sea region. Separate win-tering ducks were shot in Italy and Croatia. The great-est distance between the ringing and finding points was2,051 km. The recent shift of the mean recovery grav-ity point (280 km westwards) established during thelast decades might be a reflection of a certain redistri-bution of wintering Pochard of the Lithuanian popula-tion from the Mediterranean to the North Sea region,

240Ðvaþas S., Patapavièius R., Dagys M.

though those differences were not significant due to asmall sample. The analysis of ringing recoveries indi-cates that the Lithuanian population of CommonPochard remains highly migratory. There were almostno recoveries from the important wintering areas of theNorthwestern European population of CommonPochard, which are nearest of all to Lithuania, locatedalong the southeastern Baltic coast. The prevailing re-coveries from Western Europe could have been causedby a larger impact of hunting.

Coot

The mean recovery position of wintering Coot of theLithuanian breeding population was calculated for threesubsequent periods (1934�1959, 1960�1970, and 1971�1999).In the 1930s�1950s, the mean recovery position of win-tering Coot of the Lithuanian breeding population wasestablished in northern Italy (Fig. 4). The average dis-tance between the breeding sites and the wintering siteswas 1,490 km (Tables 8, 9).Most recoveries were received from the Mediterraneanregion, Italy and France in particular. Wintering birdswere also recorded in the Netherlands and other coun-tries of the North Sea region. Separate wintering Cootswere shot in Spain (up to 2,462 km from the breedingsite). A slight shift in their wintering grounds (250 kmnorth-westwards) occurred in the 1960s, with the re-covery gravity point established in Switzerland. This

was partly due to numerous recoveries of Coot fromLake Bodensee in Switzerland. A certain eastward shiftin the wintering grounds was observed during the lastdecades. In recent years, the mean recovery position ofwintering Coot of the Lithuanian breeding populationwas located in Austria, the average calculated distancebetween the breeding sites and the wintering sites mak-ing 1,293 km. The analysis of the ringing recoveriesindicates a possible gradual shift in the key winteringgrounds of Coot of the Lithuanian origin from the west-ern Mediterranean region to Central and NorthwesternEurope. The average distance of the migratory routehas shortened by 200 km. Recent recoveries from theCzech Republic, Hungary, Denmark, northern Germany,and Poland might also be a reflection of the changes inthe wintering grounds, though those differences werenot significant. The recovery from Belarus indicates thatthe rapidly increasing wintering population of Coot inthat country (Kozulin & Sidorenko, 2001) can includebirds of the Lithuanian population and, possibly, thosefrom other Baltic countries.

CONCLUSIONS

The analysis of long-term ringing data on Mute Swan,Mallard, Common Pochard, and Coot ringed in Lithua-nia and recovered in winter indicates a significant east-ward shift in the wintering grounds of the Lithuanianpopulation of Mute Swan and Mallard during the last

Table 8. Mean distances travelled by Coot ringed during the breeding season in Lithuania and recovered in winter and t-testsbetween the means of the subsequent time periods.

Table 9. Mean co-ordinates of finding of Coots ringed during the breeding season in Lithuania and recovered in winter.

doirepemiT ecnatsidnaeM ES egnaR n t fd P

9591–4391 20.0941 85.95 2642–936 14439.0

806.1

48

67

353.0

211.00791–0691 39.0241 81.54 8002–966 54

9991–1791 33.3921 03.96 1312–212 33

doirepemiTedutitaL edutignoL

nnaeM ES naeM ES

9591–4391 51.01 89.0 92.54 76.0 14

0791–0691 05.8 00.1 61.74 25.0 54

9991–1791 51.11 11.1 23.74 08.0 33

Table 7. Mean co-ordinates of finding of Common Pochards ringed during the breeding season in Lithuania and recovered in winter.

doirepemiTedutitaL edutignoL

nnaeM ES naeM ES

5691–3591 74.4 87.1 46.84 92.1 71

5791–6691 58.4 97.1 10.84 38.1 8

9991–6791 13.2 35.2 25.94 07.1 8

241Changes in distribution of wintering populations of waterfowl

Figure 4. Overall distribution of Coot ringed in Lithuania during the breeding season and recovered in winter and the gravitypoints for the subsequent time periods since 1934.

decades. This corroborates the results of the long-termmid-winter census of wintering waterfowl populationsconducted in Lithuania, Belarus, and the KaliningradRegion of Russia (Ðvaþas et al., 2001; Kozulin &Sidorenko, 2001; Grishanov, 2001). In the 1970s�1980s, in the Eastern Baltic region and Belarus seden-tary or just partially migratory populations of Mute Swanand Mallard established themselves. Major changes inthe wintering grounds of the local populations of MuteSwan and Mallard could be unmistakably associatedwith certain human activities affecting natural waterbodies. In the 1950s�1970s, in Lithuania and otherCentral and Eastern European countries large artificialpermanently ice-free water bodies (reservoirs of powerstations, river stretches with an influx of warm wastewaters, etc.) appeared. Another essential factor influ-encing the formation of new wintering grounds of wa-terfowl in Central and Eastern Europe is global climatechange and the increased number of mild winters ob-

served during the last decades (Ðvaþas et al., 2001).The analysis of the data stored in the Data Bank of theLithuanian Bird Ringing Centre did not reveal any sig-nificant shifts in the wintering grounds of the localbreeding population of Common Pochard. The results,however, could have been affected by a very small sam-ple of the data available. The analysis of ringing recov-eries, too, could have been biased by hunting for Com-mon Pochard practices which are different in variousregions of Europe. The extent of hunting for CommonPochard is much higher in Western Europe than in Cen-tral Europe; subsequently, more recoveries were col-lected from France and other Western European coun-tries. The mid-winter census data testify to a gradualincrease in numbers of wintering Common Pochard inLithuania and Belarus during the last decade (Ðvaþaset al., 2001; Kozulin & Sidorenko, 2001). It is likelythat in winter part of the Lithuanian breeding popula-tion of Common Pochard concentrates in the nearest

242Ðvaþas S., Patapavièius R., Dagys M.

important wintering grounds established in theSzczecin, Dars, Rugen Lagoons, and at other sites alongthe southeastern Baltic coast. Such a possibility is sup-ported by abundant recoveries of Common Pochardringed on Lake Engure in Latvia and recovered alongthe southeastern Baltic coast (Viksne, 1997).According to the t-test, recent changes in the winteringgrounds of the Lithuanian breeding population of Cootwere insignificant. In the present study, exclusively thedistribution of the birds ringed in Lithuania during thebreeding season and recovered in December�Februarywas analysed. In autumn, however, Coots leave theLithuanian breeding grounds generally earlier than mostducks and swans. Accordingly, many Coots of theLithuanian origin were recorded at their wintering sitesalready in November. The inclusion of Coots recov-ered in November into this analysis would increase theextent of the recent north-eastward shift in the winter-ing grounds of the local breeding population from200 km stated above to 373 km (the distance betweenthe gravity points for periods 1929�1958 and 1979�1999including the birds recovered in November). The resultsof the mid-winter census of Coots indicate certain recentchanges in their wintering grounds. Numbers of winter-ing Coots have recently increased in Austria and othercountries of Central Europe (Delany et al., 1999). Dur-ing the last two decades new wintering grounds of thespecies also formed in Belarus, Lithuania, and theKaliningrad Region of Russia (Ðvaþas et al., 2001;Kozulin & Sidorenko, 2001; Grishanov, 2001).

ACKNOWLEDGEMENTS

Long-term bird ringing data collected by many profes-sional and amateur ornithologists were used in thisstudy. This survey would not have been possible with-out the support of OMPO (�Migratory Birds of West-ern Palearctic�).

REFERENCES

Baillie S. 1984. The movements of migratory birds in peri-ods of severe cold weather. Report to the Council ofEurope.

Delany S., Reyes C., Hubert E., Pihl S., Rees E., Haanst-ra L., van Strien A. 1999. Results from the international

waterbird census in the Western Palearctic and South-west Asia, 1995 and 1996. Wetlands International Publ.54: 178.

Grishanov G. 2001. Changes in numbers and distribution ofwintering waterfowl populations in the Kaliningrad dis-trict of Russia. Acta Zoologica Lituanica 11 (3): 255�259.

Kozulin A., Sidorenko O. 2001. Numbers and distributionof wintering waterfowl in Belarus. Acta ZoologicaLituanica 11 (3): 260�265.

Ridgill S., Fox A. 1990. Cold weather movements of wa-terfowl in Western Europe. IWRB Spec. Publ. 13.

Ðvaþas S., Raudonikis L., Vaitkus G., Pareigis V. 1989.Wintering waterfowl in Lithuania. Vilnius: Institute ofZoology and Parasitology.

Ðvaþas S., Dagys M., Þydelis R., Raudonikis L. 2001.Changes in numbers and distribution of wintering wa-terfowl populations in Lithuania in the 20th century. ActaZoologica Lituanica 11 (3): 243�254.

Viksne J. 1997. The bird lake Engure. Riga: Jâna Sçta pub-lishers and printers Ltd.

Þalakevièius M., Ðvaþas S., Stanevièius V., Vaitkus G. 1995.Bird migration & wintering in Lithuania. ActaZoologica Lituanica. Ornithologia 2: a monograph.

ÞIEMOJANÈIØ VANDENS PAUKÐÈIØ POPULIACIJØ

PAPLITIMO POKYÈIØ ANALIZË NAUDOJANT PAUKÐÈIØ

ÞIEDAVIMO DUOMENIS

S. Ðvaþas, R. Patapavièius, M. Dagys

SANTRAUKA

Analizuojant daugiameèius þiedavimo duomenis,nustatyti pastaraisiais deðimtmeèiais Lietuvoje atsiradægulbiø nebyliø, didþiøjø anèiø, rudagalviø anèiø irlaukiø þiemavieèiø pokyèiai (ypaè ryðkûs gulbiø nebyliøir didþiøjø anèiø). Nuo 1970 m. vidutinis atstumas tarpgulbiø nebyliø perimvieèiø ir þiemavieèiø sumaþëjo413�465 km. Didþiøjø anèiø migracinis keliassutrumpëjo apie 350 km, o laukiø � apie 200 km.Rudagalviø anèiø þiemavietës per paskutinius 50 metømaþai pakito. Vandens paukðèiø þiemavieèiø pokyèiusnulëmë þmoniø ûkinës veiklos padariniai bei pasku-tiniais deðimtmeèiais ðiltëjanèios þiemos.

Received: 02 February 2001Accepted: 03 September 2001