Numbers and distribution of Long-tailed wintering Ducks in northern Europe S. Mathiasson During the last 25 or 30 years the Long-tailed Duck Clangula hyemalis has decreased considerably as a breeding species in Scandinavia and is stated to have done so also as a winter-visitor in the southern Baltic (Curry-Lindahl 1957, 1958, 1959, i960). In i960 Curry-Lindahl discussed the effect of oil pollution in the Baltic on wintering birds in general and concluded that the Long-tailed Duck was suffering more than any other species. For instance, in the winter 1954/55 the majority of about 10,000 ducks and auks found on the Swedish coast were Long-tailed Ducks and he believed that thousands were being destroyed in this way almost every year. Further, as this species keeps to the open sea in winter, he thought it very likely that even more had died than it had been possible to ascertain from shore counts. He also quoted reports that flying flocks of Long-tailed Ducks often alight on floating oil because this makes the water less rough, so that such patches serve as veritable death-traps. This situation has been closely followed by the International Council for Bird Preservation and the International Wildfowl Research Bureau. Following a suggestion by Dr Kai Curry-Lindahl at a meeting of the Executive Board of the I.W.R.B. in Wilhelmshaven, Germany, in i960, it was decided to attempt a census of wintering Long-tailed Ducks in the Baltic and the North Sea in 1961/62 and again in 1962/63, though covering only part of the area in the latter winter. All countries bordering on the Baltic participated, as did most of those round the North Sea. The censuses were organised on a national basis and the task of integrating all the data was later given to me. METHODS Unfortunately, observers in different places obtained their results in widely varying ways. Some carried out regular counts within limited areas throughout the winter; some made occasional special counts along large sections of coast or from ships at sea; and others reported what they saw by chance. In addition, very few observations referred to the same dates and a large number of Long-tailed Ducks seen at one place on one day may then have moved to an adjacent or more distant area to be recounted there on another day. It is therefore impossible to give any total figures for wintering Long-tailed Ducks in the Baltic and the North Sea, but it is worth setting out the numbers reported from different parts of the region and there are also trends

414 Long-failed Ducks in northern Europe 415 indicating the general winter distribution as well as some information on arrivals and departures, winter movements and so on. Ideally, any future investigation of this kind must have a clear framework of counts by specified methods on selected days which are the same at all places and these should be supplemented by simultaneous observa­ tions from the air and from boats. The best way of obtaining total counts would be during severe weather when these ducks gather at certain places off the coasts outside the ice.

rt>" <$%&' /J Virma

Fig. 1. Areas around the Baltic and North Sea where counts were made of Long-tailed Ducks C/angula hyemalis in 1961/62 or 1962/63 (areas providing only estimates are omitted). The overland migration from and to the White Sea was studied at Virma The countries which contributed to the survey in 1961/62 and 1962/63 were Finland, the Estonian SSR, the Lithuanian SSR, Poland, Germany, Sweden, Norway and the Netherlands (see fig. 1). Much the most extensive material came from the vast coastlines of Norway and, more particularly, Sweden where the analysis of the international results was organised by the Zoological Department of the Nordiska Museet and Skansen in Stockholm with the aid of a grant from the Swedish Game Research Council and with the extensive co-operation of the Swedish Society for the Conservation of Nature. 4*6 hong-tailed Ducks in northern Europe

NUMBERS General As already stated, it was impossible to arrive at any total figures for the population of Long-tailed Ducks wintering in northern Europe and estimates varied greatly. For example, Dr G. Bergman of Finland used radar studies to estimate about a million in the winter 1961/62. By contrast, Professor E. Kumari of the Estonian SSR regarded the neck of water between Tallinn and Helsinki (about 80 kilometres) as a gateway to a migratory stream and considered that the numbers of Long-tailed Ducks passing this way during each of the four or five autumns prior to 1963 could be roundly estimated at about 20 million 'though it is very likely that the real figure is still greater' (Kumari 1963); but this estimate greatly exceeds those of other investigators. In addition, Dr F. Goethe of Germany suggested {in litt.) that differences might be caused by large numbers of these ducks staying in the area of the White Sea during mild, ice-free winters.

Winter i$6if62 Estonian SSR The highest numbers occur in spring and autumn, and only a limited population stays for the winter. Kumari (1963) recorded that the winter 1961/62 was moderate without prolonged periods of severe frost. Nevertheless, ice kept down the numbers close inland in the and the straits of western . Further out to sea, off the west coasts of the islands of and and in certain parts of the , the species was more in evidence. Whereas inshore counts yielded only a few dozens, observers in these latter areas recorded up to 500 in a day and at Poosaspea as many as 1,200. Lithuanian SSR According to Kumari (1963), A. Vaitkovicus reported that there were several thousands in the neighbourhood of Ventes Ragas at the end of Novem­ ber and beginning of December, but that the numbers diminished rapidly towards the middle of December and that all had left by the end of that month; fluctuating numbers between 100 and 300 spent the whole winter near the coast at Palanga. Poland Information was received only from Gdansk Bay where 300 at the begin­ ning of October increased to 900 at the end of that month, to between 1,000 and 1,500 during November and to 2,000 from December to mid-February; the numbers then dropped to 1,000 in March, 200 in April and 80 in the first ten days of May, after which no more were seen (J. Sokolowski). Germany Dr F. Goethe estimated that the total numbers along the whole of the Baltic coast of Germany had been about 10,000 in recent winters; according to G. Schmidt of Wilhelmshaven, however, the population off the coast of Schleswig- Holstein (about one third of the German Baltic coast) was between 11,000 and 12,000 in 1961/62. No special reports were received from the North Sea coast of Germany, but Dr Goethe informed me that Long-tailed Ducks are scarce there and only at all frequent in hard winters, though they are more numerous and regular off the mussel banks of Amrum and Sylt. Sweden Observations were made throughout the winter both along the coast and on the open sea. In some places there were regular counts, but in others only random records. In September a single flock of 23 was the sole report and in October the Long-taikd Ducks in northern Europe 417 total was still a mere 1,126. In November, however, much higher numbers gave a figure of 20,310, and a monthly average of about 20,000 was maintained through December and January. In February only 10,631 were reported, but in March the total rose to its highest peak of 25,879. In April the figure was 17,310, in May only 1,324 and in June none. These are the totals of numbers recorded at about 70 different localities scattered along and just off the east and west coasts of Sweden; this coastline is about 2,500 kilometres on the map, but its highly indented nature means that the actual distance is 7,624 kilometres. In addition, special investigations not included in these totals were carried out by Gustaf Liljestrom, who covered 649 kilometres by motor launch from the archipelago of Ostergotland along the Swedish east coast down to Karlskrona and out to the island of Gotland. To the north of Haradsskar in the archipelago of Ostergotland he calculated a density of 84,000 Long-tailed Ducks per 100 square kilometres; while to the north of Oland his corresponding figure was no less than 250,000. These estimates give some idea of the immense numbers occurring in that region, but also show how difficult it is to make accurate counts. In the same area the observations from land produced totals of only 14,677 in January, 5,174 in February and 18,466 in March, and yet these figures represent 74%, 49% and 71% respectively of the numbers reported from the whole of the Swedish coastline during those months. Consequently, even these land-based counts are evidence of the concentrations of Long-tailed Ducks in that part. Such concentrations are not known elsewhere along the Swedish coast. Norway The total reported from inshore waters on a coastline of about 20,000 kilometres was 28,768 (table 1); this figure was thought to be much too low, how­ ever, and it was estimated that at least 50,000 winter along the coasts of Norway (Lund 1962). Reports were returned from only 44% of the coastal districts, and the 28,768 was the sum of the means of all winter counts in each district. Netherlands The situation along the shore was comparable with that on the North Sea coast of Germany: according to J. A. Eygenraam of Arnhem, a total of only 14 individuals was recorded in the winter 1961/62. On the other hand, regular counts by Commander J. J. C. Tanis off the coast of Terschelling during 1961-63 showed that Long-tailed Ducks are regular visitors to deeper water over about 500 metres from the beach: they were seen there from early October to late February, with the maxima in December when small flocks of five to 60 were recorded daily and a total of 50 to 60 per square kilometre was estimated. The numbers off the Dutch coast are thus likely to be higher than previously thought because counts are rarely made away from the shore.

Winter 1962I63 Finland Dr G. Bergman reported that not a single Long-tailed Duck was recorded round the coast during very severe ice conditions, but that a small area of the Finnish Baltic was open the whole winter and radar showed no great change in the population there between 1961/62 and 1962/63. The spring migration of the Long-tailed Duck in southern Finland was analysed by Bergman and Donner (1964). Estonian SSR According to Professor E. Kumari, the winter 1962/63 was generally very severe. In November and early December concentrations of between 20 and several hundred Long-tailed Ducks could be seen in ice-free localities, but then the western part of Estonia and most of the Gulf of Finland were frozen from mid- December. The sea stayed free of ice longest to the west of the Estonian islands— round the western end of Hiiumaa, for instance—but even there freezing occurred after i8th-20th February. Some days before that happened, between 10,000 and 15,000 Long-tailed Ducks could be counted in front of the ice barrier. 4i8 hong-tailed Ducks in northern Europe

Poland J. Sokolowski reported that the species was first seen in Gdansk Bay on loth October and that the total rose to 2,200 during ist-ioth December, but the sea was frozen from mid-December to late March and none was seen then until small numbers in the spring. Germany According to Dr F. Goethe and G. Schmidt, there were very few Long-tailed Ducks even in ice-free localities at Heiligenhafen, Fehmarnsund, Grossenbrode and Neustadt on the German Baltic coast up to the end of the year, but then some hundreds were seen along the ice from January to March. On 17th March 2,200 were recorded at Hohwachter Bucht and these numbers then increased during April until about 12,000 were seen on the 13th. Netherlands There were again very few observations along the coast, a total of only 39 individuals being reported from seven localities, including one flock of 16 inside the Waddensee near Terschelling on 13th January.

To sum up, these counts and estimates of migrating and wintering Long-tailed Ducks give some idea of the numbers involved in different parts of the Baltic and the eastern North Sea, but the figures obtained are no more than a first step and a great deal of further information is needed. In particular, it will be necessary to learn more about the numbers passing along the Estonian coast and further south, and about the concentrations wintering in various coastal areas.

GEOGRAPHICAL DISTRIBUTION As we have seen, there are indications of a very strong migration of this species through the Gulf of Finland. According to Professor E. Kumari and Dr G. Bergman, this region seems to be a bottleneck through which most of the Long-tailed Ducks coming to the Baltic pass to and from their winter-quarters. The main wintering areas, each accommodating some thousands normally and at times up to 15,000 in a single flock, appear from the reports to be in west Estonian waters, in Gdansk Bay in Poland, along the Baltic coast of Schleswig- Holstein in Germany and off the east coast of Sweden including the waters around the islands of Oland and Gotland. The figures available suggest that the most important of these areas is the east coast of Sweden where Long-tailed Ducks occur in high numbers all through the winter and where special investigations have indicated a density which has no counterpart in other reports. Judging from Norwegian data (table 1), the main winter-quarters there are in the northernmost coastal districts, no less than 63% of the Long-tailed Ducks reported being found to the north of the

Table 1. Numbers of wintering Long-tailed Ducks Clangula hyemalis reported off each province of the Norwegian coast in winter 1961/62 (Lund 1962) Long-tailed Ducks in northern Europe 419

Total coastal Number providing Total numbers administrative information on of Long-tailed Province districts Long-tailed Ducks Ducks seen

Ostfold 12 4 365 Akershus 8 0 0 Oslo 1 0 0 Buskerud 3 0 0 Vestfold 2 150 17 Telemark 5 2 325 Aust-Agder *3 4 no Vest-Agder 2 500 Rogaland 40 6 1,215 Hordaland 53 8 2,205 Sogn og Fjordane 33 5 870 More og Romsdal 66 14 2,310 Sor-Trondelag 32 10 1,380 Nord-Trondelag 31 10 1,125 Nordland 60 24 6,210 Troms 3« 19 4.403 Finnmark 17 12 7,600

TOTALS 436 122 28,768

Fig. 2. Migration pattern of Long-tailed Ducks Clangula hyemalis wintering in northern Europe. The winter distribution indicates that Norwegian populations have little connection with those movnig from the White Sea to the Baltic Arctic Circle and only 5% in the waters between Stavanger and the Swedish border. This distribution indicates that Norwegian Long- 420 hong-tailed Ducks in northern Europe tailed Ducks in general have little connection with those wintering in the Baltic. The two populations must reach their winter-quarters by different routes (fig. 2) and it seems likely that they originate from different breeding areas, the Norwegian birds being probably of Fenno-Scandian origin and the Baltic ones probably of north Russian origin. Between the wintering grounds of north Norway and those of the Baltic are areas from which very few or no wintering or migrating Long-tailed Ducks are reported, such as the Gulf of Bothnia, the west coast of Sweden, the Skaggerak and the southern North Sea.

TIMING OF MIGRATION According to Kumari (1963), the Long-tailed Ducks left the White Sea area of north Russia mainly between 2nd and 9th October in 1961, as shown by observations at Virma (see fig. 1) where some 30,000 were recorded. Generally, the migration begins there in the second half of September and reaches a peak about the beginning of October, but sometimes not until towards the middle of October; the return migration in spring is strongest in May and was outstandingly heavy in that month in 195 5 and i960. In Poland in 1961/62 the figures already given show that numbers arrived in Gdansk Bay in October (300-900) and early November (1,000-1,200) and reached a peak in late November and early December (1,500-2,000); in the spring most left in April, but 80 were still present on 10th May. In Germany Long-tailed Ducks appeared in early November and numbers increased until February or March, while the reports from the Netherlands indicated a small arrival in mid-November and a final departure in early March. In Sweden in 1961/62 the first Long-tailed Ducks were reported in mid-September, but the small numbers during October (total 1,126) indicated that the real immigration took place in November, from the middle of which month flocks of up to 2,000 were seen at several places (total 20,310); the majority of these stayed for the winter and were still present in April (total 17,310), but they then quickly dis­ appeared and the last sizable flock (500) was reported off Gotland on 13 th May. It is worth adding that continuous records of the numbers were kept throughout this winter at three different light­ houses (Svenska Bjorn, Almagrandet and Grundkallen) in the archi­ pelago ENE of Stockholm, right at the northern limit of the main wintering area, and the fluctuations at these places were almost identical. At Svenska Bjorn, for example, 4,746 were noted in Novem­ ber, 2,875 in the first week of December and only 693 in the rest of that month; from then until the end of January numbers were small and irregular and, though more were seen during February and March, these seemed likely to be involved in winter movements as the Long-tailed Ducks in northern Europe 421 birds concerned were rarely recorded more than on a single occasion. From the above we may conclude that Long-tailed Ducks migrate to winter quarters in the Baltic region mainly during October, having left the White Sea area in the first week of that month. Numbers increase on both sides of the Baltic (Sweden and Poland) during November,

WINTER MOVEMENTS There is a tendency for the numbers of Long-tailed Ducks to increase in the south-western Baltic during the winter, probably because of climatic conditions in the eastern and middle parts. The winter 1962/63 was generally very severe and by mid-December most of the Gulf of Finland and some areas of the coastal waters of Estonia were ice-bound. Before that, in November and early December, Long- tailed Ducks had occurred at many places. By late January and early February even much of the sea in the westernmost part of the Gulf of Finland was iced over and on i8th-2oth February a mass south-west migration of Long-tailed Ducks took place in Estonia as conditions became worse and worse; throughout March the shore waters were completely covered with ice. In April large numbers arrived on the German Baltic coast, about 12,000 being recorded at Westmarkelsdorf (the northern part of Fehmarn) on the 13th and 'still more further out in the sea'. On the 14th there were 6,320 at this locality, while 1,352 and 945 were counted flying to the north-west and north-east respec­ tively. G. Schmidt suggested, following Naumann (1904), that large numbers had left the Baltic altogether in the severe ice conditions of 1962/63 to winter in the North Sea or further south and that the concentrations seen at Fehmarn and other places along the German Baltic coast were these same birds resting on their way back. Observa­ tions of Long-tailed Ducks flying WSW between Kiel and Neustadt in February and a corresponding return from the west in April might seem to support this hypothesis. Dr F. Goethe informed me, however, that those at Fehmarn could not have come from the Elbe estuary or the North Sea German Bight and the same held for Dutch waters where only a handful was reported. We have seen that large numbers (10,000 to 15,000 in one locality) were still present in western Estonia until i8th-2oth February when they disappeared to the south-west, and the westward movement noted between Kiel and Neustadt may have been part of the same migration, but we still do not know where these birds spent the latter part of the winter nor whether any of them really left the Baltic.

FLOCK SIZE The Long-tailed Duck has a social tendency to form large flocks 422 lj>ng-taikd Ducks in northern Europe within its main winter-quarters and the average size of such flocks becomes smaller the further they are from these areas. For example, the chief wintering grounds in Sweden include the coast of Smaland and the island of Gotland where 92 (64.8%) of 142 flocks in 1961/62 were of more than 40 birds and totalled 29,847, while the 50 flocks of less than 40 totalled only 937; 13 flocks exceeded 500, the largest ones in the 2,000-3,500 range. By contrast, in the Gulf of Bothnia, which is outside but quite close to the main wintering grounds, only 28 (35«5%) OI" 79 flocks exceeded 40 birds and these totalled only 2,899; while off the west coast of Sweden, which is further from the chief areas, just four (4.6%) of 87 flocks were of more than 40 and totalled a mere 458 (while the 83 others totalled only 706). The small numbers seen off the Dutch coast are a further indication of this trend. In severe weather, however, large concentrations may be forced west of the normal winter-quarters, as we have seen happened in 1962/63 when a single flock of 12,000 was recorded at Fehmarn and some (including a party of 16) reached the Netherlands.

DISTRIBUTION OF SEXES Table 2 summarises data on the sexes of Long-tailed Ducks in the flocks along the Swedish coast in 1961/62. Possible sources of error include variation in the ability of observers, the likelihood of con­ fusing young males and females, and the fact that some of the propor­ tions were based on random samples which may not have taken sufficient note of any uneven distribution of the sexes within the flocks. Nevertheless, the figures in individual reports were surprisingly close to the general trends in table 2. The most interesting facts which emerge are the preponderance of males in the main Swedish winter- quarters and the preponderance of females in the surrounding areas; the mean for the whole Swedish coast showed 825% excess of males.

Table 2. Distribution of sexes of Long-tailed Ducks Clangula hyemalis along the coast of Sweden in 1961/62 The Smaland figures include those from Oland and the Uppland ones those from the Stockholm archipelago Total Province records Males Percentage Females Percentage

Skane 73 3,618 57-2% 2,698 42-8% Blekinge 157 2,851 54.6% 2,369 45-4% Holland 10 23 47-o% 26 53-o% Smaland 98 25,164 6i.5% 15.735 38-5% Gotland I? 9»27i 55-5% 7.432 44-5% Bohuslan 54 328 48.9% 343 51-1% Sodermanland 59 3.955 56-9% 2,991 43-1% Uppland 232 6,269 40.1% 9,347 59-9% Gulf of Bothnia 42 275 31-1% 608 68.9% "Long-tailed Ducks in northern Europe 423 Table 3. Numbers of Long-tailed Ducks Clangula hyemalis in waters of different MM 'Ml depths along the coast of Sweden in 1961/62 g|||g Depth in Total Total Percentage metres records ducks of all

0-5 75 9,406 25-9% 5-10 55 2,730 7-5% 10-15 25 20,018 55-3% 15-20 9 1,926 5-3% 20-25 10 1,883 5-2% 25-30 3 12 30-35 11 383 35-40 1 3 40-45 1 8

HABITAT AND FOOD Table 3 demonstrates that no less than 55.3% of the feeding Long- tailed Ducks seen along the Swedish coast were swimming in waters 10-15 metres deep and a further 33.4% in still shallower places. Practically all were in waters less than 25 metres deep, though near Harnosand a party of 15 was recorded diving in a depth of 40-50 metres. Many observers stressed a connection with shoals and banks, and the link appears to be one of food. Molluscs, crustaceans, small fishes and 'seaweed' were among the items specifically mentioned and, in particular, the edible mussel Mytilus edulis seems to play a most important role. For example, 2,000-3,500 Long-tailed Ducks were seen between 15 th November and 13 th December 1961 in a restricted area east of Oland where shoals 5-20 metres below the surface have, according to local fishermen, the largest populations of mussels in the region. Six females and one male, shot above another shoal to the north on 1st November 1964 and sent to the Natural History Museum at Goteborg, had nothing but shells and shell fragments of mussels in their stomachs. Parallel observations outside Sweden were few, but Dr F. Goethe also reported that the species was rather more frequent and regular around the mussel banks of Amrum and Sylt than on other parts of the German North Sea coast.

SUMMARY The Long-tailed Duck Clangula hyemalis has decreased as a breeding species in Scandinavia and is believed to have done so in its winter quarters in the southern Baltic. The International Wildfowl Research Bureau attempted a winter census in the Baltic and North Sea in 1961/62 and 1962/63. Countries contributing were Finland, the Estonian SSR, the Lithuanian SSR, Poland, Germany, Sweden, Norway and the Netherlands, but methods varied from regular local censuses to counts along large sections of coast or from ships, as well as chance observations. Total figures were therefore impossible, but this paper summarises the reports by countries, assesses the main wintering areas and discusses timing of migration, winter move­ ments, flock size, sex ratios, habitat and food. Radar was used in Finland to estimate a winter population of a million, and the 424 Lang-tailed Ducks in northern Europe westward autumn passage through the Gulf of Finland was believed to involve as many as 20 million, but actual coastal counts were much smaller. Nevertheless, these suggested that important wintering areas included west Estonian waters (10,000-15,000 in February), Gdansk Bay in Poland (2,000+ in December-February), the Baltic coast of Schleswig-Holstein (11,000-12,000) and south-east Sweden (20,000 in November-January, 26,000 in February). Migration overland between the White Sea and the Baltic is greatest in early October and May. In the main winter quarters most flocks were of 40-3,500 (142 flocks averaged 217), whereas in peripheral areas few flocks exceeded 40 (87 flocks averaged only 13). In Sweden a preponderance of males in the main winter quarters was partly offset by an excess of females elsewhere, but there was a mean 25% excess of males. Practically all feeding Long-tailed Ducks were in waters less than 25 metres deep, mostly 10-15 metres or less; the edible mussel Mytilus edulis seems to be an important food.

REFERENCES BERGMAN, G., and DONNER, K. O. 1964. 'An analysis of the spring migration of the Common Scoter and the Long-tailed Duck'. Acta Zool. Fenn., 105:1-59. CURRY-LINDAHL, K. 1957. 'Serious situation with regard to Swedish populations of Long-tailed Duck (Clangula byemalis)'. I.W.R.B. Newsletter, y. 26-29. 1958. 'Vertebratfaunen i Sareks och Padjelantas fjallomraden'. Fauna och Flora, 53: 97-149. 1959. Vira Figlar 1Norden. Stockholm, vol 1: 557. i960. 'Serious situation with regard to Swedish populations of the Long-tailed Duck (Clangula byemalis)'. l.W.R.B. Newsletter, 10: 15-18. KOMARI, E. 1963. 'Number dynamics of some migratory seabirds on the White Sea and in the eastern part of the Baltic Sea'. Communications Baltic Commission for Study of Bird Migration, Tartu, 2: 67-79. LUND, H. M.-K. 1962. 'Telling av havellebestanden'. N, J. F. F. Tidsskr,, 91: 440-442. MATHIASSON, S. 1964. 'Alfageln—nagra resultat av inventeringen i Nordeuropa 1961-1962'. Sver. Nat., 55: 196-201. NAUMANN, J. A. 1904. Naturgeschichte der Vogel Mitteleuropas. Gera. vol X. S. Mathiasson, Naturhistoriska Museet, Goteborg 11, Sweden