ACROCEPHALUS 36 (164/165): 21-43, 2015 10.1515/acro-2015-0002 Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Spomladanska selitev vodnih ptic in ujed na zadrževalniku Medvedce (Dravsko polje, SV Slovenija) Dejan Bordjan1 1 Ulica 8. februarja 50, Dravski dvor, SI-2204 Miklavž na Dravskem polju, Slovenija, e-mail: dejan.bordjan@gmail.com Spring migration of birds, particularly waterbirds and raptors, was monitored from dawn till dusk from an observation point located on the levee on the northern side of the Medvedce reservoir (Dravsko polje, NE Slovenia) in three separate years (1-17 Mar 2009; 25 Mar-10 Apr 2011; 28 Feb-12 Apr 2012). In all three years, 42,045 individuals of 89 species (66 waterbirds, 23 raptors) migrated over the site. 38,238 of these were waterbirds. The most numerous species was Lapwing Vanellus vanellus (11,813 individuals), followed by Black-headed Gull Chroicocephalus ridibundus (10,515 individuals). In total, 3807 migratory storks, raptors and Cranes Grus grus were counted. Harriers (2303 individuals) were by far the most numerous group. The prevailing direction of migration was SW-NE. Half of all migrating birds were observed in the altitudinal belt between 10 and 100 m above ground level. Harriers were mostly observed up to 100 m above ground level, whereas storks, other raptors and Cranes were observed most often in the altitudinal belt between 100 and 500 m above ground level. The highest numbers of waterbirds were observed between 10 and 100 m above ground level. In the first five hours after sunrise, 61.3% of all waterbirds, 44.0% of all storks and raptors and only 20.5% of Cranes were observed. Although other parts of Dravsko polje have never been studied in such detail, it is possible that a significant portion of migrating birds from a larger area gathers at this site. This study confirms the importance of the area for migrating and staging birds, especially for Great Egret Ardea alba, Marsh Circus aeruginosus and Hen Harriers C. cyaneus, Osprey Pandion haliaetus, Crane, Ruff Calidris pugnax and Black-headed Gull that all reached at least 0.1% of their respective biogeographic populations. Internationally significant are particularly the numbers of migrating Marsh (1079 individuals in 2012) and Hen Harriers (408 individuals in 2012), as there are only few sites where these species migrate in such high numbers in spring. Key words: waterbirds, raptors, spring migration, Medvedce, Marsh Harrier, Circus aeruginosus, Hen Harrier, Circus cyaneus Ključne besede: vodne ptice, ujede, spomladanska selitev, Medvedce, rjavi lunj, Circus aeruginosus, pepelasti lunj, Circus cyaneus 1. Introduction Many migratory bird species use well established migration routes (Newton 2008). Waterbirds generally follow one of the many flyways known around the world. Flyways are areas used by a number of species with similar geographical ranges and migration habits. However, the distribution and movements of many waterbird species are more continuous and complex, and do not allow ready division into populations (Delany & Scott 2006). Moreover, some species may even switch between well-established flyways during their lifetime (Guillemain et al. 2005). Finally, birds found at particular stop-over sites may 21 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) belong to several different fly ways (Delany & Scott 2006). On the other hand, many raptors, specifically soaring ones, congregate at bottlenecks (Agostini & Loghozzo 1995, Jonzen & Pettersson L999, Zalles & Bildstein 2000, Schneider-Jacoby 2001, Agostini et al. 2003, Newton 2008, Premuda et al. 2008, Probst 2009, Denac 2010, Michev et al. 2012) and thus take markedly different flight routes from those used by waterbirds or passerines (Newton 2008). This means that in Europe most waterbirds and many raptors using flapping flight migrate in E-W or NE-SW directions (Shydlovskyy 2000, Hake et al. 2001, Agostini et al. 2003, Leitao & Peris 2004, Davidson & Stroud 2006, Delany & Scott 2006, Liminana et al. 2007, Premuda et al. 2008, Strandberg et al. 2008). Soaring birds, on the other hand, migrate towards the nearest bottleneck and then continue southwards (Meyburg et al. 1998, Berthold et al. 2002, Meyburg & Meyburg 2007). Raptors were counted at several sites in western Slovenia both in spring and autumn, but there was only one study that utilized daily counts lasting the entire day, every day during migration (Denac 2010). This study confirmed assumptions of several previous incomplete counts that Breginjski Stol near Kobarid was a bottleneck for migrating raptors, the majority of which were Honey Buzzards Pernis apivorus. In eastern Slovenia, no such counts have been carried out, although Dravsko polje was listed as an important area for migrating raptors, especially Harriers Circus sp. and Ospreys Pandion haliaetus (Zalles & Bildstein 2000). No such study exists for waterbirds or passerines. This is at least partly due to their habit of nocturnal migration along a broad front (Newton 2008). Passerine migration is monitored at several more or less regular ringing sites (Vrezec et al. 2014), while waterbirds are counted at the national level during mid-winter counts (e.g. Božič 2014). Daily counts were performed in Sečovlje saltpans (Jančar 1995) and at reservoirs on the Drava River for monitoring migrating Chlidonias terns (L. Božičpers. comm.). Systematic, but not daily, counts were performed e.g. at the Medvedce reservoir Figure 1: Study area with the observation point (scale 1:20,000) Slika 1: Območje raziskave z opazovalno točko (merilo 1:20.000) 22 AcRO CEPHALUS 36 (164/165): 5-20, 2015 (Bordjan & Božič 2009), lakes in the Gorenjska region (Jančar et al. 2007), Drava River in Maribor (Logar & Božič 2014) and Lake Cerknica (Bordjan 2012). Birds moving to and from Lake Ptuj were monitored for two whole days along the Drava River and some migrants were also observed (Stumberger & Sorgo 1995). Several papers have been published on migration at Dravsko polje (Vogrin 1997, 1998A, b, c, 1999) but none with daily point counts. The systematic counts of waterbirds and raptors in ten-day periods were implemented at the Medvedce reservoir in 2002 (Bordjan & Božič 2009) and are still being conducted. Although the counts were not designed to detect migration, observations were gathered that suggested substantial migration for some species. These data along with many observations at other parts of Dravsko polje (Božič 1992, Vogrin 1997, Bordjan 2007) were the actual reason for this study. Its aim was to evaluate size, spatial and temporal characteristics of spring migration of waterbirds and raptors at the Medvedce reservoir. 2. Study area and methods 2.1. Study area Migration was monitored at the Medvedce water reservoir southeast of Pragersko in northeastern Slovenia (46°22'08" N; 15°40'04" E). The reservoir, which is utilized as a fishpond, is surrounded by intensively managed meadows and arable fields. It is situated at the southwestern corner of Dravsko polje approximately midway between Pohorje Mts (1543 m a.s.l.) and Mt Boč (978 m a.s.l.) at an altitude of239 m a.s.l. The site is surrounded by low rolling hills to the west and south, and by flatlands to the north and east. Further characteristics of the study area were described in more detail by Bordjan & Božič (2009). 2.2. Methods Spring migration was monitored in three separate years. Counting periods were as follows: 1-17 Mar 2009 (17 days); 25 Mar-10 Apr 2011 (17 days); 28 Feb-12 Apr 2012 (45 days). In 2009, the primary focus of monitoring was the migration of Lapwings Vanellus vanellus, thus the period was chosen accordingly. Periods in 2011 and 2012 were chosen based on previous experiences to cover the peak migration of Marsh Harriers Circus aeruginosus. The observation point was on the levee on the northern side of the reservoir (Figure 1). Daily monitoring lasted from dawn till dusk and was shortened only on days with prolonged rain and fog. Due to various reasons, monitoring was not conducted for one day in 2009 and 2011 respectively and for five days in 2012 (Table 1). Birds roosting in reed beds at the study site were counted separately. Observers were constantly scanning the surrounding area in all directions with binoculars and spotting scopes (20-60x magnification). Apart from the weather conditions described in Denac (2010) we also noted the presence of fog and relative visibility. The latter was described as good, average or poor. In general, poor was used in case of fog, low clouds or drizzling rain. Each morning upon arrival at the site, weather was described and any significant change noted thereafter. Species were identified to the lowest possible taxonomic level. If possible, individuals were also sexed and aged. Data on their numbers, exact time of observation and direction of flight were recorded as by Denac (2010). Codes used for the height of individual flight were as follows: 0: < 10 m above ground, 1: 10-100 m above ground, 2: 100 — 500 m above ground, 3: birds visible with binoculars, but not with the naked eye, 4: birds visible only with spotting scopes. Although no exact measurements were made, 3 and 4 were taken as an estimate of > 500 and > 1000 m above ground respectively. To analyse the intensity of migration by time of day we used the time elapsed from the local sunrise, which was at 6.37 hrs on 28 Feb and 6.25 hrs on 10 Apr, with a transition to European Summer Time on 25 Mar. To compare migration characteristics among different groups of birds, the ^-test was used. Spearman's rank coefficient was used for correlations between variables. P-values lower than 0.05 were considered significant. The main foci of the study were waterbirds and raptors. Other species observed during the study are presented in Appendix 1. Due to some similarities in migration (e.g. using thermals, diurnal migration), Cranes Grus grus and storks were analysed together with raptors. Movements of known local breeding pairs and local movements to and from feeding sites such as flooded fields were excluded from the analysis. The distinction between true migration and local movements was made by observers on-site. For estimating the migration of waterbirds, which migrate mostly during the night, the daily difference in their numbers was used. Only days with positive (higher number on the following day) were counted. For example, if the daily numbers for a particular species were 100, 95, 36, 50, 12, 112, only the first, the fourth and the sixth days were counted. In that case the estimate was calculated as follows: 100 (the number on the first day) + (50 — 36 (the difference between the fourth and third days)) + (112 — 12 (the difference between the sixth and fifth days)) = 214. 23 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Table 1: The number of observers and weather conditions for all three monitoring periods Tabela 1: Število opazovalcev in vremenske razmere v vseh treh obdobjih monitoringa No. of No Cloud Date/ Datum observers/ Št. opazovalcev survey/ Brez popisa cover/ Oblačnost Precipitation/ (%) Padavine Fog/ Megla Visibility/ Vidljivost Wind (intensity, direction)/ Veter (jakost, smer) 1. 3. 1 0 Yes Average / Povprečna 0-2, SW 2. 3. 1 100 Good / Dobra 0 3. 3. 1 100 Yes Average / Povprečna 0 4. 3. 1 * 0 Rain / Dež Bad / Slaba 1, W 5. 3. 1 100 Rain / Dež Average / Povprečna 0 6. 3. 2 10 Good / Dobra 2, changing direction/ spremenljiva smer 7. 3. 1 60 Good / Dobra 2, SW 8. 3. 3 10 Good / Dobra 1, SE 0 H 9. 3. 1 100 Rain / Dež Good / Dobra 2, NW 10. 3. 1 20 Good / Dobra 1, SE 11. 3. 1 10 Good / Dobra 2 12. 3. 1 93 Good / Dobra 1 13. 3. 1 60 Good / Dobra 1 14. 3. 1 33 Good / Dobra 1 15. 3. 2 80 Good / Dobra 16. 3. 1 100 Good / Dobra 2, SW 17. 3. 1 40 Good / Dobra 1, SW 25. 3. 2 0-70 Good / Dobra 0-4, SW 26. 3. 3 20-80 Good / Dobra 3-4, NE 27. 3. 2 50-100 Good / Dobra 0-1, SE 28. 3. 1 * 100 Rain / Dež Yes Average to Bad/ Povprečna do slaba 1-2, SE 29. 3. 1 10-70 Yes Average to Bad/ Povprečna do slaba 0-1, changing direction/ spremenljiva smer 2011 30. 3. 2 0 Yes In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 1-3, SW 31. 3. 2 0-10 Good / Dobra 0-2, changing direction/ spremenljiva smer 1. 4. 2 50-100 Occasional rain/ Občasen dež Good / Dobra 0-1, changing direction/ spremenljiva smer 2. 4. 2 0 Good / Dobra 0 3. 4. 1 0-I5 Good / Dobra 0-1, SW 4. 4. 1 5-80 Good / Dobra 0-4, changing direction/ spremenljiva smer 5. 4. 1 20-70 Occasional rain/ Občasen dež Good / Dobra 1-3, NW, NE 24 ÄCROCEPHALÜS 36 (164/165): 21-43, 2015 Continuation of Table 1 /Nadaljevanje tabele 1 Date/ Datum No. of observers/ Št. opazovalcev No survey/ Brez popisa Cloud cover/ Oblačnost Precipitation/ (%) Padavine Fog/ Megla Visibility/ Vidljivost Wind (intensity, direction)/ Veter (jakost, smer) 6. 4. 1 10-60 Good / Dobra 0-1, NW 7- 4. 2 10-85 Good / Dobra 0-2, SW 8. 4. 1 30-100 Good / Dobra 0-3, NE, SW 9- 4. 3 10 Good / Dobra 1-3, SW 10. 4. 4 0 Good / Dobra 1, changing direction/ spremenljiva smer 28. 2. 1 0 Average / Povprečna 1, SW 29. 2. 1 * 0 Average / Povprečna 1, SW 1. 3. 3 40-50 Good / Dobra 1-2, NE, SE 2. 3. 2 0 Good / Dobra 0-1, E 3. 3. 2 0-100 In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 0-1, NE 4. 3. 2 60 Good / Dobra 1-2, E 5. 3. 1 60-100 Average / Povprečna 0-2, E, NE 6. 3. 0 * 50 Good / Dobra 1 7. 3. 1 0 Good / Dobra 1 8. 3. 1 30 Good / Dobra 1 9. 3. 1 50 Good / Dobra 1 H 10. 3. 2 0 Good / Dobra 2, NE 0 2 11. 3. 2 30-100 Good / Dobra 0-2, changing direction/ spremenljiva smer 12. 3. 1 90 Good / Dobra 1 13. 3. 1 20-100 In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 0-2, changing direction/ spremenljiva smer 14. 3. 1 5 Good / Dobra 1 15. 3. 1 30 Good / Dobra 1 16. 3. 5 0 Yes In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 1-3, changing direction/ spremenljiva smer 17. 3. 2 0 Good / Dobra 4, SW 18. 3. 1 75-100 Good / Dobra 4-6, SW 19. 3. 1 0-60 Yes In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 1, changing direction/ spremenljiva smer 20. 3. 0 * 60 Good / Dobra 2 21. 3. 1 0 Yes In the morning Bad, later Good / Slaba zjutraj, dobra pozneje 1, changing direction 25 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Continuation of Table 1 /Nadaljevanje tabele 1 Date/ Datum No. of observers/ Št. opazovalcev No survey/ Brez popisa Cloud cover/ Oblačnost Precipitation/ (%) Padavine Fog/ Megla Visibility/ Vidljivost Wind (intensity, direction)/ Veter (jakost, smer) 22. 3. 3 0 In the morning Average, later Good/ Povprečna zjutraj, dobra pozneje 1, changing direction/ spremenljiva smer 23. 3. 1 10-30 Average / Povprečna 1-3, SW 24. 3. 2 10-70 Good / Dobra 0-2, N 25. 3. 4 10-90 Good / Dobra 0 26. 3. 1 10 Good / Dobra 0-2, NW, NE 27. 3. 2 0-30 Good / Dobra 0 28. 3. 2 0 Good / Dobra 0 29. 3. 2 100 Good / Dobra 0-1, SE, NE 30. 3. 1 77 Good / Dobra 1-2, SW, NE 31. 3. 1 0-80 Good / Dobra 0-3, changing direction/ spremenljiva smer 1. 4. 1 0-40 Good / Dobra 0-2, SE, NE 2. 4. 1 10 Good / Dobra 2, SW 3. 4. 1 10 Average / Povprečna 4, SW 4. 4. 1 10-90 Good / Dobra 0-3, SW 5. 4. 1 70 Average / Povprečna 1 6. 4. 0 * 100 Rain / Dež Average / Povprečna 2 7. 4. 2 50-100 Rain / Dež Bad / Slaba 1, changing direction/ spremenljiva smer 8. 4. 1 100 Snow / Sneg Average / Povprečna 2, NE 9. 4. 1 0-30 Good / Dobra 0-1, changing direction/ spremenljiva smer 10. 4. 0 * 40 Average / Povprečna 2 11. 4. 1 50-100 Average / Povprečna 0-1, SW 12. 4. 1 70 Average / Povprečna 0-1, changing direction/ spremenljiva smer Mallard Anas platyrhynchos and Cormorant Phalacrocorax carbo were excluded from this, since the former regularly winters at the site and breeds in significant numbers (Bordjan & Božič 2009). Moreover, its peak migration occurs earlier in the year (Cramp 1998). Finally, Mallards regularly fly between the study site and other water bodies at Dravsko polje. Cormorants roost along the Drava River and fly to the study site every morning, returning in the evening. Different numbers could therefore simply reflect the change in feeding areas between days. For the Great White Egret Ardea alba, numbers from roost counts were used. 3. Results 3.1. Migration totals In all three years, 42,045 individuals of 89 species (66 waterbirds, 23 raptors) were counted. The highest 26 ÄCROCEPHALÜS 36 (164/165): 21-43, 2015 number for both groups was counted in 2012 and the lowest in 2009 (Table 2). In total, four species had more than 1000 individuals (Tables 3 and 4), two of which had more than 10,000 (Lapwing; Black-Headed Gull Chroicocephalus ridibundus). 25 (28.1%) species were encountered in only one year, while 38 (42.7%) were observed in all three years (Tables 3 and 4). 3.2. Waterbirds In total, 38,238 migratory waterbirds were counted. The highest number was recorded in 2012 and the lowest in 2011 (Table 2). The most numerous species on migration was Lapwing with 11,813 individuals (31.0%) closely followed by Black-headed Gull with 10,515 (27.5%) individuals. Ten species each presented more than 1% of all migrating waterbirds but only Ruff Calidris pugnax reached more than 2% with 6078 individuals (15.7%; Table 3). Out of 66 observed species of waterbirds the highest number was observed in 2012 (58) and the lowest in 2009 (34). 29 species were seen in all three years, while 18 were seen in one year only (Table 3). The migration of waterbirds peaked in mid-March (Figure 2). The strongest migration was observed on 12 Mar 2012 when 2326 individuals were counted. In all three years, more than 1000 migrating individuals were counted on eight days. On average, 520 individuals (SD 385) were observed per day (lowest in 2011: 323 individuals/day; SD 124 and highest in 2012: 661 individuals/day; SD 430). There was no obvious trend in the number of migrating waterbirds through the entire period (RS = -0.14, P = 0.234, df = 64), but if the period was divided in two parts the number of migrating individuals rose till 13 Mar (RS = 0.43, P = 0.026, df = 23) and declined subsequently (RS = -0.43, P = 0.002, df = 39). 3.3. Storks, raptors and Cranes Grus grus In total, 3807 migratory storks, raptors and Cranes were counted; the most in 2012 and the fewest in 2009 (Table 2). Of 23 registered species, nine were observed in all three counting periods, while five were observed both in 2011 and 2012 (Table 4). One species was observed only in 2011 and six only in 2012. Harriers were by far the most numerous migrants in this group, accounting for 60.5% (Table 4). They accounted for more than half birds in this group in all observation periods (from 55.0% in 2012 to 88.0% in 2009). Among harriers, Marsh Harriers were the most numerous. The 5% threshold for migrating storks, raptors and Cranes in any given year was attained by four other species (Table 4): Hen Harrier (2009: 52.6%; 2012: 15.0%), Buzzard Buteo buteo (2012: 11.6%), Osprey Pandion haliaetus (2011: 8.2%) and Crane (2011: 8.0%; 2012: 24.1%). Raptors were observed on migration from the first day of monitoring onwards (Figure 3). The highest number was counted on 7 Apr 2012 with 173 individuals. More than a hundred individuals were counted on ten days during the survey. On average in all three years, 51 individuals (SD 42) were observed per day. Considering separate years 20 (2009; SD 15), 45 (2011; SD 29) and 66 (2012; SD 46), individuals were counted on an average day. The number of migrating storks, raptors and Cranes increased towards the beginning of April (RS = 0.29, P = 0.012, df = 73). 3.4. Migration characteristics The majority of birds arrived to the area from the SW (30.5%) and W (28.3%) and departed towards the NE (44.7%) and E (28.9%) (Figure 4). Although this was generally true for both groups of birds, there was a Table 2: Numbers of waterbirds and storks, raptors and Cranes Grus grus counted during spring migration in 2009, 2011 and 2012 at Medvedce reservoir Tabela 2: Število vodnih ptic ter štorkelj, ujed in žerjavov Grus grus, preštetih med spomladansko selitvijo v letih 2009, 2011 in 2012 na zadrževalniku Medvedce Waterbirds / Vodne ptice Storks, raptors, Cranes Grus grus/ Štorklje, ujede, žerjavi Grus grus All / Vse Migratory / Selivke All / Vse Migratory / Selivke 2009 152.9° 6303 561 325 2011 18646 5355 1031 765 2012 73694 26580 3610 2717 Total / Skupaj 107630 38238 5223 3807 27 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Table 3: Number of migratory waterbirds counted during spring migration in 2009, 2011 and 2012 at Medvedce reservoir Tabela 3: Število preštetih vodnih ptic med spomladansko selitvijo v letih 2009, 2011 in 2012 na zadrževalniku Medvedce Species / Vrsta 2009 2011 2012 Species / Vrsta 2009 2011 2012 Cygnus olor i9 ?o ii6 Gallínula chloropus i 6 4 Anser albifrons ^ Fulica atra I0? i6 6Í4 Anser anser î5 68 Himantopus himantopus 47 i? Tadorna tadorna 6 Charadrius dubius 99 ii Anas penelope 54 9 ^ Charadrius hiaticula i Anas strepera i7 7 49 Charadrius morinellus i Anas crecca i54 55 409 Pluvialis apricaria i? 5 94 Anas carolinensis i Pluvialis squatarola i Anas platyrhynchos 688* ?i6* ii8o* Vanellus vanellus ??5i i665 6796 Anas acuta ii5 84 Calidris alpina 6 8 Anas querquedula iii i55 4ii Calidris pugnax Í09 ii48 45ii Anas clypeata ii io6 i94 Lymnocryptes minimus i Netta rufina ? ii Gallinago gallinago 69 86 569 Aythya nyroca iî 7 i9 Numen ius phaeopus 7 i8 Aythya fuligula îi 5i i?6 Numenius arquata i ii i9 Aythya fuligula x marila i Actitis hypoleucos 5 i9 Bucephala clangula ? i i Tringa ochropus i? 6i ii9 Mergellus albellus ? Tringa erythropus 7 ?6 Mergus serrator i Tringa nebularia i 46 94 Mergus merganser i4 77 Tringa stagnatilis ?6 4 Phalacrocorax carbo ?5 9 ?oi Tringa glareola i85 i6i Botaurus stellaris i i4 Chroicocephalus ridibundus ii55 5i0 8840 Nycticorax nycticorax 4 Larus melanocephalus i 6 Egretta garzetta i Larus canus ii6 i? 50i Ardea alba Iii I00 4i6 Larusfuscus 5 4 Ardea cinerea i? io4 ?I0 Larus michahellis 9i i7 i64 Ardea purpurea 4 Larus cachinnans ii i0i Tachybaptus ruficollis i9 i48 i97 Alcedo atthis i 4 Podiceps nigricollis i 7 Charadrius sp. 4 Porzana porzana i Tringidae 6 Porzana parva i Laridae i * Only maximum counts are given and not added to total sum. / Podana so le najvišja števila, ki niso prišteta celotni vsoti. significant difference in both arrival (x2 = 940.1; P < 0.001; df = 7) and departure directions (x2 = 567.6; P < 0.001; df = 7) between the two groups. Storks, raptors and Cranes arrived mostly from the SW and W (83.4%), whereas waterbirds arrived from other direction on almost half occasions (46.3%). Storks, raptors and Cranes departed mostly towards the NE (62.0%), whereas in waterbirds the direction of departure was more evenly distributed between the NE (42.0%) and E (29.9%). 50.7% of all migrating birds were observed at altitudes between 10 and 100 m above ground (Figure 5). Harriers were significantly more often observed at lower heights than storks, other raptors and Cranes (f = 567.1; P < 0.001; df = 4). Harriers 8 ÁCROCEPHALÜS 36 (164/165): 21-43, 2015 Table 4: Number of storks, raptors and Cranes Grus grus counted during spring migration in 2009, 2011 and 2012 at Medvedce reservoir Tabela 4: Število štorkelj, ujed in žerjavov Grus grus preštetih med spomladansko selitvijo v letih 2009, 2011 in 2012 na zadrževalniku Medvedce Species / Vrsta 2009 2011 2012 Species / Vrsta 2009 2011 2012 Ciconia ciconia 28 19 Aquila heliaca 1 Milvus migrans 12 6 Pandion haliaetus 9 63 100 Milvus milvus 2 Falco tinnunculus * 5 13 Circus aeruginosus "5 496 1079 Falco columbarius 5 Circus cyaneus 171 24 408 Falco subbuteo 2 Circus macrourus 2 4 Falco peregrinus 3 5 19 Circus pygargus 1 3 Asio flammeus 1 1 Accipiter gentilis 10 2 24 Grus grus 61 656 Accipiter nisus 9 9 43 Circus sp. 8 1 Buteo buteo 5 32 316 Falco sp. 1 Buteo lagopus 2 Raptor / Ujeda 2 " The species was observed, but none of the individuals were counted as migratory. / Vrsta je bila opazovana, vendar noben osebek ni bil štet kot seleč. 200 180 160 Ü § 140 0 120 f 100 1 80 C S 60 o z 40 20 0 2009 2011 2012 I U 28 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 II III IV Date / Datum Figure 2: Phenology of migrating waterbirds counted in 2009, 2011 and 2012 between the end of February and the first half of April at Medvedce reservoir Slika 2: Fenologija selečih se vodnih ptic, preštetih v letih 2009, 2011 in 2012 med koncem februarja in prvo polovico aprila na zadrževalniku Medvedce were observed in the two lower belts (< 10 m: 40.4%; 10-100 m: 42.1%) in similar percentage, whereas storks and other raptors were observed most often (48.6%) at altitudes between 100 and 500 m (Figure 3). Cranes were observed at that altitude in an even higher percentage (66.5%) and their altitudinal distribution was significantly different from that of storks and raptors (X2 = 32.1; P < 0.001; df = 4). Waterbirds also had a different altitudinal distribution from other groups, with the highest numbers observed between 10 and 100 m above ground (54.1%). In the first five hours after sunrise, almost two thirds ofall waterbirds (61.3%), fewer than halfofall storks and raptors (44.0%) and only 20.5% ofCranes were observed. 29 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) The peak in migration of waterbirds was in the first two hours after sunrise (Figure 6). Thereupon, migration receded (RS = -0.92, P < 0.001, df = 13). Most Cranes migrated over Medvedce in the late afternoon with 67.7% more than 9 hours after sunrise (Figure 6). Storks and raptors, which reached a peak in daily migration between the fourth and fifth hours after sunrise, had a significantly different hourly distribution from that of waterbirds (X2 = 1135.8, P < 0.001, df = 13). Waterbirds reached 50% of migrating individuals in the first four hours after sunrise, storks and raptors in the first six hours and Cranes in the first 11 hours after sunrise. 2500 2000- ¡S 1500- I 1000- 500- 2009 2011 2012 M 111 28 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 II III IV Date / Datum Figure 3: Phenology of migrating storks, raptors and Cranes Grus grus counted in three separate years between the end of February and the first half of April at Medvedce reservoir Slika 3: Fenologija selečih se štorkelj, ujed in žerjavov Grus grus, preštetih v treh letih med koncem februarja in prvo polovico aprila na zadrževalniku Medvedce Storks, raptors and Cranes Grus grus/ Štorklje, ujede in žerjavi Grus grus N 60 -r W 1 i E Waterbirds / Vodne ptice N 60 W E Figure 4: Percentage of waterbirds and storks, raptors and Cranes Grus grus using certain direction of migration to (black) and from (grey) the Medvedce reservoir in 2009, 2011 and 2012 Slika 4: Odstotek smeri prihodov (črno) in odhodov (sivo) vodnih ptic ter štorkelj, ujed in žerjavov Grus grus na zadrževalniku Medvedce v letih 2009, 2011 in 2012 30 S S AcRO CEPHALUS 36 (164/165): 5-20, 2015 3.5. Selected species 3.5.1. Marsh Harrier Circus aeruginosus The earliest observations of Marsh Harrier during this study were on 1 Mar 2009 and 2 Mar 2012. Migration increased through the observation period and reached its peak at the end of March, when it receded slightly and reached a second peak in the first half of April (Figure 7). The highest number of individuals (94) in one day was recorded on 7 Apr 2012, while the second highest (88) was on 31 Mar >1000 >500 100-500 m 10-100 <10 Waterbirds / Vodne ptice Grus grus Circus sp. Other raptors and storks / Ostale ujede in štorklje 20 40 % 60 80 Figure 5: The altitudinal distribution of different groups of birds migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 5: Višinska porazdelitev ptic, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 45 -i 40 -35 -30 -25 -20 -15 -10 -5 -0 Storks and raptors / Štorklje in ujede Grus grus Waterbirds / Vodne ptice 3-4 4-5 5-6 6-7 7-8 Time from local sunrise / Čas od sončnega vzhoda (h) 9-10 10-11 Figure 6: Hourly distribution of birds migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 6: Urna porazdelitev ptic, selečih se čez zadrževalnik Medvedce v letih 2009, 2011 in 2012 31 0 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) 2011. In total, 1690 Marsh Harriers were observed. The observations were distributed among individual years as follows: 115 (2009), 496 (2011), 1079 (2012). Most observations were of single birds (85.4%), with five being the highest number in a single flock. Out of all Marsh Harriers observed during the count, 479 (28.4%) individuals also roosted in a reed bed within the reservoir. 100 90 80 H J ig 70 -8 >1000 >500 100-500 ~ 10-100 <10 10 20 30 40 50 60 70 % Figure 14: The altitudinal distribution of Ospreys Pandion haliaetus migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 13: Urna porazdelitev ribjih orlov Pandion haliaetus, Slika 14: Višinska porazdelitev ribjih orlov Pandion haliaetus, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 140 120 - 100 - 80 - > 60 - 40 - 20 - 0 2011 2012 I I I 28 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 II III Date / Datum Figure 15: Phenology of Cranes Grus grus migrating over the Medvedce reservoir in 2009, 2011 and 2012 8 6 4 2 0 0 V Slika 15: Fenologija žerjavov Grus grus, selečih se čez zadrževalnik Medvedce v leta 2009, 2011 in 2012 35 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) 700 i 600 - 500 - 400 - > 300 - ■ 200 - 100 - 2009 2011 I 2012 llll . I 28 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 II III IV Date / Datum Figure 16: Phenology of Lapwings Vanellus vanellus migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 16: Fenologija prib Vanellus vanellus, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 >1000 >500 100-500 .■h 10-100 <10 10 20 30 % 40 50 60 Figure 17: The altitudinal distribution of Lapwing Vanellus vanellus migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 17: Višinska porazdelitev prib Vanellus vanellus, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 were observed. In both years when monitoring was conducted in the first half of March, the number of migrating Lapwings exceeded 600 individuals on two separate days (2009: 8 Mar - 617, 15 Mar - 663; 2012: 4 Mar - 627, 12 Mar - 637). 49.4% of all observed flocks numbered 11-100 individuals and 46.8% had fewer than 10 individuals. The largest flock had 438 individuals and was observed on 12 Mar 2012. More than half (54.5%) of all migrating Lapwings were observed between 10 and 100 m above ground (Figure 17). 36 3.5.6. Black-headed Gull Chroicocephalus ridibundus In 2009 and 2012, Black-headed Gulls were observed from the beginning of the count period. 1150 individuals were counted in 2009, more than half of which (590) on the last day. The number of Black-headed Gulls rose steadily from the start to the middle of March (Figure 18). In contrast, in 2012 the number of individuals was already high at the beginning of March (Figure 18), but nevertheless rose towards the middle of the month, with a peak on 12 Mar with 935 individuals. The number of individuals fell rapidly after 16 Mar and remained low until the end of the counting period. The migration was weak throughout the counting period in 2011, when the survey started after the migration peak of this species. An equal percentage of flocks (43.8% each) contained fewer than 10 and 11-100 individuals, while the largest flock had 488 individuals and was observed on 12 Mar 2012. The majority of Black-headed Gulls (58.9%) migrated at altitudes between 10 and 100 m (Figure 19). 4. Discussion This study showed that substantial numbers of waterbirds and raptors migrate over the Medvedce reservoir, some in conservationally important numbers. 0 AcRO CEPHALUS 36 (164/165): 57-67, 2015 1000-1 900- 800- > £ ■Q e 700- O >55 600- w (O 500- -0 400- c T5 300- 0 Z 200- 100- 0 2009 2011 I 2012 llllll I I J J I I J ■ I I I I 28 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 II III IV Date / Datum Figure 18: Phenology of Black-Headed Gulls Chroicocephalus ridibundus migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 18: Fenologija rečnih galebov Chroicocephalus ridibundus, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 >1000 >500 100-500 .■h 10-100 <10 10 20 30 40 50 60 70 % Figure 19: The altitudinal distribution of Black-headed Gull Chroicocephalus ridibundus migrating over the Medvedce reservoir in 2009, 2011 and 2012 Slika 19: Višinska porazdelitev rečnih galebov Chroicocephalus ridibundus, selečih se čez zadrževalnik Medvedce leta 2009, 2011 in 2012 The main direction of migration was SW-NE, with the flight altitude mainly below 100 m above ground. Taxonomic groups of birds differed in their phenology, migration direction, as well as hourly and altitudinal distribution. The main migration direction SW-NE observed in this study is found in many avian taxa (Hake et al. 2ooi, Agostini et al. 2003, Leitâo & Peris 2004, Davidson & Stroud 2006, Delany & Scott 2006, Liminana et al. 2007, Meyburg & Meyburg 2007, Premuda et al. 2008, Strandberg et al. 2008, MiNGOZZi et al. 2013) across different flyways in Europe. Although species observed at the study site may belong to different flyways, all were flying in the same general direction, reflecting a local geographical constraint. The study site is surrounded by high hills in the northwest and in the south, but it is currently unknown whether birds congregate along those hills. Data from synchronized counts, done near Celje 30 km to the southwest from the study area, indicate that at least some, but not all, waterbirds, raptors and Cranes follow a direct route from Celje to Medvedce (M. Gamserpers. comm.). Mt Boč and Pohorje Mts are both more than 5 km away, so the question arises, what percentage ofmigrating birds from a larger area converges at the site. Migrating raptors were also observed in the nearby Dravinja valley (Vrezec 1997) and on the edges of Pohorje Mts (own data). As mentioned above, not all birds migrating through the lowland area near Celje arrive at the study area (M. Gamser pers. comm.). Although individuals and even flocks on migration were observed at other sites on Dravsko polje (VoGRiN 1997, L. Božič pers. comm., own data), their numbers were considerably smaller. On the other hand, higher numbers of migrating Montagu's Harriers Circus pygargus and sometimes Red-Footed Falcons Falco vespertinus were observed a few kilometres to the northeast of the site (L. Božič pers. comm.). Although other parts of Dravsko polje have never been studied in as much detail, my assumption is that a 0 35 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Table 5: Conservationally important species on spring migration at Medvedce reservoir that reach at least 0.1% of the biogeographical population. Populations of raptors were calculated from BirdLife International (2004), while populations of waterbirds were gathered from http://wpe.wetlands.org/. Tabela 5: Varstveno pomembne vrste, ki na spomladanski selitvi čez zadrževalnik Medvedce dosegajo najmanj 0,1 % svoje biogeografske populacije. Populacije ujed so bile izračunane na podlagi BirdLife International (2004), populacije vodnih ptic pa na podlagi podatkov na strani http://wpe.wetlands.org/. No. of ind. Percentage of counted in 2012/ biogeographic Št. preštetih os. 1% threshold/ population / Odstotek Biogeographic population/ Species / Vrsta leta 2012 1 % prag biogeografske populacije Biogeografska populacija 416 460 1079 3423 408 1340 100 274 656 900 6796 72300 4521 12200 8840 11800 significant portion of migrating birds from a larger area gathers at the study site. Abundance and availability of food resources are the major factors determining distribution of migrants (Newton 2008). Thus, some waterbirds, e.g. herons, waders, gulls and at least Osprey among raptors congregate at the site to feed on migration. In contrast to the strategy of making a full stop to forage and deposit fuel, a fly-and-forage migration strategy is possible for species that fly extensively during foraging or rely on search flights to find their prey either on ground or on water (Strandberg & Alerstam 2007). The use of this strategy has been demonstrated for Ospreys both on their autumn and spring migration (Strandberg & Alerstam 2007), while conclusive evidence is still lacking for Marsh Harriers (Strandberg etal. 2008). Numbers of migrating birds observed during the study were considerably higher than those from counts in ten-day periods (Bordjan & Božič 2009). While for most species the longer period of dedicated observation can explain the difference in abundance, the higher numbers of Cranes can also be attributed to the significant rise in the number of Cranes migrating through the new migration corridor over northern Italy (Mingozzi et al. 2013). Although Mingozzi et al. (2013) studied Cranes on autumn migration, birds W C & SE Europe/ Black Sea & Mediterranean Europe Europe Europe North-east & Central Europe/ North Africa Europe, W Asia/ Europe, N Africa & SW Asia Northern Europe & Western Siberia / West Africa East Europe/ Black Sea & East Mediterranean from this flyway most likely include migrants from Slovenia both on autumn and spring migrations. For some species, numbers were lower than expected. One such species is Lapwing. Considerably higher numbers were observed in 2006 (993 individuals in only a part of the day) (Bordjan & Božič 2009), and in flooded fields in 1995 (20003000) (Bračko 2009) and in 2014 (1882; own data). The estimate could be even higher for the study itself, since on 14 Mar 2012 only 90 individuals were counted due to fog, while 1,060 were counted at Lake Ormož at the same time (B. Štumberger pers. comm.), indicating strong migration possibly overlooked due to poor visibility. Lapwings are known to perform large-scale movements in response to adverse weather conditions, evacuating large regions in a short time (Vepsalainen 1968, Wernham et al. 2002). Nevertheless, it is entirely possible that Lapwings did not migrate over the study area on that day, as they migrate along a broad geographic front (Gillings & Wilson 2009). Black-headed Gull is another such species, with daily maxima of 1055 and 2527 individuals on 15 Mar 2006 and on 13 Mar 2010 respectively (Bordjan & Božič 2009, own data). The number of waders fluctuates at Medvedce in parallel with water levels and the extent of flooded arable land in the surroundings during migration. Ardea alba Circus aeruginosus Circus cyaneus Pandion haliaetus Grus grus Vanellus vanellus Philomachus pugnax Chroicocephalus ridibundus °-9 0.3 0.2 0.4 0.6 0.1 0.4 0.8 36 AcRO CEPHALUS 36 (164/165): 57-67, 2015 They are considerably more numerous in years with low water levels (e.g. 2003, 2011, 2012) than in years with higher water levels (e.g. 2004 and 2008) (Bordjan & Božič 2009, own data). Thus the numbers of waders counted in 2012 probably represented the upper limit in numbers of wader migration, including Ruff. Not only the number of individuals, also the number of species is higher for the study compared to the ten-day period counts (Bordjan & Božič 2009). Between 2002 and 2008, when one count was done per period, the number of observed species per ten-day period in March ranged from 18 to 42 (average 27). Between 2009 and 2014 (excluding periods covered by the study), when two counts per period were done, the number of species ranged from 29 to 60 (average 37), while during the study it ranged from 37 to 64 (average 48). Thus, with one count per ten-day period approximately half of all species present are detected, while with two counts more than two thirds are detected. Marsh Harriers migrate along a broad front and concentrations at bottlenecks are not as pronounced as in other raptor species (Agostini & Panuccio 2010). The migration route across the Strait of Messina is the most frequently used flyway for this species in the Western Palearctic with 1621 to 3074 birds counted during spring between 1996 and 2000 (Corso 2001). Only few birds are counted in spring at the Strait of Gibraltar (usually fewer than 200) (Agostini 2001), Eilat (annual mean of 178) (Leshem & Yom-Tov 1998) and the Bosphorus (negligible numbers) (Collman & Croxall 1967). The numbers recorded at Medvedce in 2012, when the counting period was designed to coincide with peak migration of the species, therefore appear to be important at the continental level. The migration of Marsh Harriers at Medvedce had two peaks: one in late March and another in the first half of April. Mediterranean watchpoints have a single migration peak between 1 and 10 Apr (Agostini 2001, Corso 2001, Panuccio et al. 2004, Panuccio et al. 2013). Marsh Harriers migrate across the Strait of Messina until the end of May (Corso 2001). Birds are present at Medvedce and Dravsko polje throughout late spring and summer (Vogrin 1997, Bordjan & Božič 2009). Even though it is difficult to distinguish migrants from breeders and non-breeding summer visitors with certainty, spring migration of Marsh Harriers at Medvedce seems to continue well into May. In agreement with previous research (Agostini & Panuccio 2010), males at Medvedce reservoir migrated earlier than females, albeit with considerable overlap. Hen Harriers are even less numerous at bottlenecks than Marsh Harriers: in spring, 3-84 were counted at the Strait of Messina (Corso 2001), negligible numbers at Eilat (Leshem & Yom-Tov 1998) and the Strait of Gibraltar (Bensusan et al. 2007) and up to 250 at Falsterbo in autumn (Kjellen & Roos 2000). Considering only spring migration, the number of Hen Harriers migrating over the Medvedce reservoir is internationally important. Migration habits of harriers (Marsh, Montagu's and Pallid Circus macrourus) were studied using radar in southern Israel (Spaar & Bruderer 1997). Harriers as a group migrated at a lower average altitude than other raptors and soaring birds, which was also the case in our study. In Marsh Harrier, there was a trend towards increasing flight altitude later in the day. As in our study, Marsh Harriers in Israel started migrating soon after sunrise. By combining flapping (around sunrise and sunset) and soaring flight (around midday), harriers were able to use the entire day for migration. Although flight styles were not studied at Medvedce, the hourly distribution confirmed that harriers migrated throughout the day. This study confirmed the importance of the area for migrating and staging birds. Apart from Marsh and Hen Harriers, other species counted in important numbers are Great Egret, Osprey, Crane, Lapwing, Ruff and Black-Headed Gull. For the three raptors, these numbers are also the highest counted so far in Slovenia (Tome et al. 2005, Bordjan & Božič 2009, Denac 2010, Denac et al. 2011, Bordjan 2012). The number of Black-Headed Gulls is higher only on Lakes Ptuj and Ormož (Denac et al. 2011). More Lapwings probably gather in some years at Ljubljansko barje (Tome et al. 2005) and the Drava River (Denac et al. 2011). While none of the above mentioned species reached more than 1% of the biogeographic population, all but Lapwing attained more than 0.1%. (Table 5). This also justifies the position of these species as qualifying species for IBA Črete (Denac et al. 2011). In 2012, when the monitoring period lasted for 45 days, 2717 raptors and Cranes were counted. Taking into account reasons for overlooked or missed birds of prey listed by Denac (2010) and discussed below, the actual number of migrating raptors is probably even higher. Some species of raptors start migrating before and some after the monitoring period used in the study (Cramp 1998). The number migrating in April and May might be similar to the number migrating during the study period (Denac 2010). The migration of the most numerous species, Marsh Harrier, does not end till mid-May (Strandberg et al. 2008) and significant number may still pass by that time (Premuda et al. 2008), especially juveniles (Strandberg et al. 2008). On most, but not all, monitoring days two observers 35 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) were present. Moreover, on five days in 2012 no counts were made at all. At the same time, the percentage of overlooked individuals is higher with flapping flyers than soaring flyers. It is also higher with single individuals and small groups (majority of observation in this study) than with larger flocks (Sattler & Bart 1984). Raptors can migrate in unfavourable weather conditions, such as headwinds or rain (Denac 2010). On several days, the visibility was lowered due to rain or fog. More individuals were probably overlooked during days with fog, since it was usually present until 9.00 hrs, a time by which a significant number of individuals had already been registered on clear days. In some species, nocturnal migration is known (Russell 1991, DeCandido et al. 2006). This is especially true for falcons (33-34% of migration by night) and harriers (15-20%) (Meyer et al. 2003), the most numerous group observed at Medvedce. These results warrant further migration studies at Medvedce, which should be designed to focus on the migration of key species, such as Marsh and Hen Harriers. A species-targeted count should be able to yield reliable estimates of annual migration totals and address some of the methodological limitations of this study. Acknowledgments: I thank all the volunteers who invested their time and energy in standing at the site for the entire day and sending the collected data afterwards: Tilen Basle, Blaž Blažič, Dominik Bombek, Luka Božič, Benjamin Denac, Katarina Denac, Mitja Denac, Jernej Figelj, Matej Gamser, Jurij Hanžel, Karin Kanc Hanžel, Tomaž Jančar, Alijana Pivko Kneževič, Aleksander Koren, Aleksander Kozina, Janez Leskovar, Cvetka Marhold, Urška Martinc, Matija Medved Mlakar, Jure Novak, Alen Ploj, Mojca Podletnik, Matjaž Premzl, Barbara Robnik, Andreja Slameršek, Željko Šalamun, Rebeka Šiling, Tanja Šumrada, Aleš Tomažič, Davorin Tome, Tina Unuk, Zlata Vlahčič. 5. Povzetek V treh ločenih letih (1. do 17. 3. 2009; 25. 3. do 10. 4. 2011; 28. 2. do 12. 4. 2012) je v organizaciji avtorja prispevka potekal spomladanski monitoring pretežno vodnih ptic in ujed. Pticam smo sledili vse od zore do mraka z opazovalnice, postavljene na nasipu na severni strani zadrževalnika Medvedce (Dravsko polje, SV Slovenija). Skupno je bilo v teh obdobjih preštetih 42.045 osebkov 89 različnih vrst (66 vodnih, 23 ujed), selečih se prek Medvedc. Od teh je bilo 38.238 vodnih ptic. Najštevilnejša je bila priba Vanellus vanellus (11.813 os.), njej pa je sledil rečni galeb Chroicocephalus ridibundus (10.515 os.). Preštetih je bilo tudi 3807 selečih se štorkelj, ujed in žerjavov Grus grus. Daleč najštevilnejši so bili lunji (2302 os.). Prevladujoča smer selitve je bila JZ-SV. Polovica vseh selečih se ptic je bila opazovana v višinskem pasu med 100 in 500 metri nad tlemi. Lunji so leteli večinoma v pasu do 100 metri nad tlemi, štorklje, druge ujede in žerjavi pa najpogosteje v višinskem pasu med 100 in 500 metri. Največje število vodnih ptic je bilo opazovano v pasu med 10 in 100 metri. V prvih petih urah po sončnem vzhodu je bilo zabeleženih 61,3 % vseh vodnih ptic, 44,0 % vseh štorkelj in ujed in samo 20,5 % žerjavov. Čeprav drugi deli Dravskega polja niso bili še nikoli preučevani tako podrobno, je povsem mogoče, da se pomemben delež selečih se ptic iz večjega območja zbira prav na preučevani lokaliteti. Sicer pa je raziskava potrdila velik pomen območja za seleče se in tu počivajoče ptice, še posebno za veliko belo čapljo Ardea alba, rjavega Circus aeruginosus in pepelastega lunja C. cyaneus, ribjega orla Pandion haliaetus, žerjava, togotnika Calidris pugnax in rečnega galeba, ki so tu vsi dosegli najmanj 0,1 % svojih biogeografskih populacij. Mednarodnega pomena je še posebno število tako selečih se rjavih Circusaeruginosus (1079 os. v letu 2012) kot pepelastih lunjev C. cyaneus (408 os. v letu 2012), saj je znanih le nekaj lokalitet, kjer se ti vrsti spomladi selita v tako velikem številu. 6. References AGOSTINI N. (2001): Spring migration in relation to sex and age of Marsh Harriers Circus aeruginosus over a central Mediterranean island. - Ardeola 48 (1): 71-73. AGOSTINI N., Coleiro C., Panuccio M. (2003): Autumn migration of Marsh Harriers (Circus aeruginosus) across the central Mediterranean in 2002. - The Ring 25 (1/2): 47-52. AGOSTINI N., Logozzo D. (1995): Autumn migration of Honey Buzzards in Southern Italy. - Journal of Raptor Research 29 (4): 275-277. AGOSTINI N., Panuccio M. (2010): Western Marsh Harrier (Circus aeruginosus) migration through the Mediterranean Sea: a review. - Journal of Raptor Research 44 (2): 136-142. Bensusan K. J., Garcia E. R. J., Cortes J. E. (2007): Trends in abundance of migrating raptors at Gibraltar in spring. -Ardea 95 (1): 83-90. Berthold P., Bossche W. V. D., Jakubiee Z., Kaatz C., KaaTZ M., Querner U. (2002): Long-term satellite tracking sheds light upon variable migration strategies of White Storks (Ciconia ciconia). - Journal of Ornithology 143: 489-495. BirdLife International (2004): Birds in Europe: population estimates, trends and conservation status. BirdLife Conservation Series No. 12. - BirdLife International, Cambridge. Bordjan D. (2007): Črni škarnik Milvus migrans. -Acrocephalus 28 (134): 129. 36 AcRO CEPHALUS 36 (164/165): 57-67, 2015 BoRDJAN D. (2012): Vodne ptice in ujede Cerkniškega polja (južna Slovenija) v letih 2007 in 2008, s pregledom zanimivejših opazovanj do konca leta 2010. - Acrocephalus 33 (152/153): 25-148. BoRDJAN D., Božič L. (2009): Pojavljanje vodnih ptic in ujed na območju vodnega zadrževalnika Medvedce (Dravsko polje, SV Slovenija) v obdobju 2002-2008. -Acrocephalus 30 (141/142/143): 55-163. Božič L. (1992): Spomladanski prelet sršenarja Pernis apivorus prek Maribora. - Acrocephalus 13 (54): 144145. Božič L. (2014): Rezultati januarskega štetja vodnih ptic leta 2014 v Sloveniji. - Acrocephalus 35 (160/161): 73-83. Bračko F. (2009): Priba Vanellus vanellus. - Acrocephalus 30 (141/142/143): 175-176. Collman J. R., Croxall J. P. (1967): Spring migration at the Bosphorus. - Ibis 109 (3): 359-372. CoRSo A. (2001): Raptor migration across the Strait of Messina, southern Italy. - British Birds 94 (4): 196-202. Cramp S. (ed.) (1998): The complete birds of the western Palearctic on CD-ROM. - Oxford University Press, Oxford. Davidson N. C., Stroud D. A. (2006): African-Western Eurasian Flyways: current knowledge, population status and future challenges. pp. 63-73. In: BoERE G. C., GalbraiTH C. A., Stroud D. A. (eds.): Waterbirds around the world. - The Stationery Office, Edinburgh. DeCandido R., Bierregaard R. O., Martell M. S., BiLDSTEiN K. L. (2006): Evidence of nocturnal migration by Osprey (Pandion haliaetus) in North America and Western Europe. - Journal of Raptor Research 40 (2): 156-158. Delany S. N., ScoTT D. A. (2006): Wetlands International's Flyway Atlas series: establishing the geographical limits of waterbird populations. pp. 574-581. In: BoERE G. C., GalbraiTH C. A., Stroud D. A. (eds.): Waterbirds around the world. - The Stationery Office, Edinburgh, UK. Denac K. (2010): Census of migrating raptors at Breginjski Stol (NW Slovenia) - the first confirmed bottleneck site in Slovenia. - Acrocephalus 31 (145/146): 77-92. Denac K., Mihelič T., Božič L., Kmecl P., Jančar T., FiGELJ J., Rubinic B. (2011): Strokovni predlog za revizijo posebnih območij varstva (SPA) z uporabo najnovejših kriterijev za določitev mednarodno pomembnih območij za ptice (IBA). Končno poročilo (dopolnjena verzija). Naročnik: Ministrstvo za okolje in prostor. - DOPPS -BirdLife Slovenia, Ljubljana. Hake M., Kjellen N., AlersTAM T. (2001): Satellite tracking of Swedish Ospreys Pandion haliaetus: autumn migration routes and orientation. - Journal of Avian Biology 32: 47-56. GiLLiNGS S., Wilson A. (2009): Northern Lapwing Vanellus vanellus. pp. 129-133. In: Delany S., DoDMAN T., Stroud D. (eds.): An atlas of wader populations in Africa and western Eurasia. - Wetlands International, Wageningen. GuiLLEMAiN M., Sadoul N., Simon G. (2005): European flyway permeability and abmigration in Teal Anas crecca, an analysis based on ringing recoveries. - Ibis 147: 688696. JANČAR T. (1995): Spremljanje številčnosti vodnih ptičev v Sečoveljskih solinah. - Acrocephalus 16 (71): 108-112. Jančar T., Kmecl P., Mihelič T., Kozinc B. (2007): Pregled vodnih ptic Blejskega in Bohinjskega jezera ter jezera HE Moste (Gorenjska, SZ Slovenija). - Acrocephalus 28 (135): 141-158. JONZÉN N., PETTERSSON J. (1999): Autumn migration of raptors on Capri. - Avocetta 23 (2): 65-72. KjELLÉN N., ROOS G. (2000): Population trends in Swedish raptors demonstrated by migration counts at Falsterbo, Sweden 1942-97. - Bird Study 47 (2): 195-211. LeitAo D., Peris S. (2004): The origin of Lapwings Vanellus vanellus and Golden Plovers Pluvialis apricaria wintering in Portugal. - Ornis Fennica 81 :49-64. Leshem Y., Yom-Tov Y. (1998): Routes of migrating soaring birds. - Ibis 140: 41-52. Liminana R., SOUTULLO A., Urios V. (2007): Autumn migration of Montagu's harriers Circus pygargus tracked by satellite telemetry. - Journal of Ornithology 148: 517-523. Logar K., Božič L. (2014): Letna dinamika pojavljanja vodnih ptic na reki Dravi med Mariborskim jezerom in jezom Melje (SV Slovenija). - Acrocephalus 35 (160/161): 5-24. Meyburg B.-U., Meyburg C., Barbraud J.-C (1998): Migration strategies of an adult Short-toed Eagle Circaetus gallicus tracked by satellite. - Alauda 66 (1): 39-48. Meyburg B.-U., Meyburg C. (2007): Quinze années de suivi de rapaces par satellite. Alauda 75: 265-286 (English translation). Meyer S. K., Spaar R., Bruderer B. (2003): Sea crossing behaviour of falcons and harriers at the southern Mediterranean coast of Spain. - Avian Science 3 (2/3): 153-162. Michev T. M., Proeirov L. A., Karaivanov N. P., Michev B. T. (2012): Migration of Soaring birds over Bulgaria. -Acta Zoologica Bulgarica 64 (1): 33-41. Mingozzi T., Storino P., Venuto G., Alessandria G., Arcamone E., Urso S., Ruggieri L., Massetti L., Massolo A. (2013): Autumn migration of Common Cranes Grus grus through the Italian Peninsula: new vs. historical flyways and their meteorological correlates. -Acta Ornithologica, 48 (2):165-177. Newton I. (2008): The migration ecology of birds. -Academic Press, London. Panuccio M., Agostini N., Barboutis C. (2013): Raptor migration in Greece: a review. - Avocetta 37: 1-7. Panuccio M., Agostini N., Massa B. (2004): Spring migration at Ustica, southern Italy. - British Birds 97 (8): 400-414. Panuccio M., Agostini N., Mellone U. (2005): Autumn migration strategies of honey buzzards, black kites, marsh and Montagu's harriers over land and over water in the Central Mediterranean. - Avocetta 29: 27-32. Premuda G., Gustin M., Pandolei M., Sonet L., Cento M. (2008): Spring raptor migration along the Adriatic coast (Italy): a comparative study over three sites. - Avocetta 32: 13-20. Probst R. (2009): Der Greifvogelzug im Unteren Gailtal im Herbst 2009. Bericht von BirdLife Österreich, Landesgruppe Kärnten, an das Amt der Kärntner 35 D. BoRDJAN: Spring migration of waterbirds and raptors at Medvedce reservoir (Dravsko polje, NE Slovenia) Landesregierung, Abteilung 20 - Landesplannung, UAbt. Naturschutz, Feldkirchen. RUSSELL R. W (1991): Nocturnal flight by migrant "diurnal" raptors. - Journal of Field Ornithology 62 (4): 505-508. SATTLER G., Bart J. (1984): Reliability of counts of migrating raptors: an experimental analysis. — Journal of Field Ornithology 55 (4): 415—423. SCHNEIDER-JACOBY M. (2001): Lastovo - a new bottleneck site for the migratory Honey Buzzards Pernis apivorus? -Acrocephalus 22 (108): 163-165. Shydlovskyy I. V. (2001): Peculiarities of Migrations of the Lapwing (Vanellus vanellus) in Western Ukraine. -Vestnik zoologii, 35(5): 61—67. SPAAR R., BRUDERER B. (1997): Migration by flapping or soaring: flight strategies of Marsh, Montagu's and Pallid Harriers in southern Israel. - Condor 99: 458-469. Strandberg R., AlersTAM T. (2007): The strategy of fly-and-forage migration, illustrated for the osprey (Pandion haliaetus). - Behavioral Ecology and Sociobiology 61: 1865-1875. Strandberg R., Klaassen R. H. G., Hake M., Olofsson P., THORUP K., AlersTAM T. (2008): Complex timing of Marsh Harrier Circus aeruginosus migration due to pre-and post-migratory movements. - Ardea 96 (2): 159-171. ŠERE D. (2009): Kratko poročilo o obročkanih ptičih v Sloveniji, 1983-2008. - Scopolia Suppl. 4: 111-174. Štumberger B., Šorgo A. (1995): Dnevni prelet vodnih ptic v dravski loki pri Ptuju - prezimovanje ali selitev. -Acrocephalus 16 (68/69/70): 72-78. Tome D., Sovinc A., TRONTELJ P. (2005): Ptice Ljubljanskega barja. Monografija DOPPS št. 3. - Društvo za opazovanje in proučevanje ptic Slovenije, Ljubljana. Vepsalainen K. (1968): The effect of the cold spring 1966 upon the Lapwing (Vanellus vanellus) in Finland. - Ornis Fennica 45 (2): 33-47. Vogrin M. (1997): Occurrence and passage of Marsh Harrier Circus aeruginosus, Hen Harrier Circus cyaneus and Osprey Pandion haliaetus in northeastern Slovenia. - Ring 19 (1/2): 59-63. Vogrin M. (1998A): Prelet in pojavljanje sivke Aythyaferina v Krajinskem parku Rački ribniki - Požeg v severovzhodni Sloveniji. - Acrocephalus 19 (89): 109-114. Vogrin M. (1998B): Prelet in pojavljanje togotnika Philomachus pugnax na Dravskem polju. - Acrocephalus 19 (90/91): 155-158. Vogrin M. (1998c): Occurrence and passage of Wood sandpiper Tringa glareola and Green sandpiper Tringa ochropus on the Dravsko polje, north-eastern Slovenia. -Wader Study Group Bulletin 87: 55-58. Vogrin M. (1999): Migration of Garganey Anas querquedula and Teal Anas crecca in north-eastern Slovenia. - Ornis svecica 9: 19-22. VREZEC A. (1997): Ujede in sove Dravinjske doline. - Falco 12: 17-20. Vrezec A., Fekonja D., ŠERE D. (2014): Obročkovalska dejavnost in pregled najdb obročkanih ptic Slovenije v letu 2013. - Acrocephalus 35 (160/161): 25-58. Wernham C. V., Toms M. P., Marchant J. H., Clark J. A., Siriwardena G. M., Baillie S. R. (2002): The migration atlas: movements of the birds of Britain and Ireland. - T & A D Poyser, London. Zalles J. I., Bildstein K. L. (eds.) (2000): Raptor watch. A global directory of raptor migration sites. BirdLife Conservation Series No. 9. - BirdLife International, Cambridge. Prispelo / Arrived: 30. 4. 2015 Sprejeto / Accepted: 30. 11. 2015 36 ÁCROCEPHALÜS 36 (166/167): 109-132, 2015 APPENDIX 1 / DODATEK 1: The number of migrating birds at Medvedce reservoir in 2009, 2011 and 2012 not systematically analysed in the paper Število osebkov selivk čez zadrževalnik Medvedce v letih 2009, 2011 in 2012, katerih selitev v članku ni sistematično analizirana 2009 2011 2012 2009-2012 Species / Vrsta 1. 3. - 17. 3. 25. 3. - 10. 4. 28. 2. - 12. 4. Columba oenas i6i 19 1018 1198 Columba palumbus 274 719 1447 2440 Streptopelia decaocto 1 1 Apus apus 8 8 Upupa epops 1 1 Corvus monedula 10 10 Corvus frugilegus 64 64 Remiz pendulinus 15 !5 Parus major 8 8 Alauda arvensis i 940 941 Riparia riparia 5 5 Hirundo rustica 8 1542 155° Delichon urbica 167 167 Hirundine sp. / Vrsta lastovke 1000 1000 Phylloscopus collybita i 1 2 Bombycilla garrulus 75 75 Sturnus vulgaris 8446 9611 i8057 Turdus pilaris 1534 24 589 2147 Turdus iliacus 1 1 Turdus viscivorus 4 4 8 Phoenicurus phoenicurus 1 I Oenanthe oenanthe 2 2 Motacilla flava 479 479 Motacilla alba i5i i5i Anthus pratensis 7 28 35 Anthus cervinus 1 1 Anthus spinoletta i 3 4 Anthus sp. 5i4 5i4 Fringilla coelebs 233 233 Chloris chloris 4 6 10 Carduelis carduelis 12 12 Linaria cannabina 106 106 Emberiza schoeniclus i5 1183 1198 Miliaria calandra 1 1 Total / Skupaj 10525 781 19139 30445 71