SEEN - SE European Bird Migration Network
The magnitude and timing of autumn and spring migration of soaring birds in NE Bulgaria

Dimitar Vladimirov Dimitrov
Bulgarian Academy of Sciences, Institute of Zoology, BLVD. Tzar Osvoboditel N:1, SOFIA 1000, Bulgaria

The magnitude and timing of autumn and spring migration of 30 species of soaring birds were studied in one point in NE Bulgaria (43o10`N; 27o26`S). Observation was carried out from the ground by observers with binoculars and telescope from 23.03. to 30.04. (38 days) in spring and from 1.08. to 31.10. (88 days) in autumn of 2005. The most numerous species was the White Stork (Ciconia ciconia) comprising more than 80% of all migrants both in spring and autumn. From all registered diurnal migrants 30 species were soaring birds: 26 species of medium and large-sized raptors, 4 species of waterfowl soaring birds (pelicans and storks). The birds of prey were presented by 26 species from 3 families and one order with most numerous species the Lesser Spotted Eagle Aquila pomarina 40%, Common Buzzard Buteo buteo 25% and Honey Buzzard Pernis apivorus 20%. The rest of registered migratory birds included 53 species. The peak of spring migration was in the period between 7 and 11 April when over 36% of the soaring birds were registered. Most intensive migration in the spring was observed before noon, between 9 h and 13 h when 75% of soaring birds passed. The peak in magnitude was in the middle of the day (12-13 h.) with 30% of registered migrants. The maximum of autumn migration was between 21 and 30 August when 60% of migrants passed the studied region. Two peaks were recorded, first before noon 10h ? 11h with 16% and afternoon 15h -16 h with 14% of the birds. For the whole autumn the main migratory flow (54%) passed between 9h and 13 h. The migratory directions of all observed birds were distributed between 328o - 16o in spring and 153o ? 203o in autumn (Rayleigh's test r = 0.91, p < 0.001). The strong influence of the local topography and winds are most probably explanations for the similar directions of the observed species. Location of the important thermals and concentration of soaring migrants were identified for the studied region. The results are of high conservation value concerning conflict between development of the wind power energy and bird migration along Bulgarian Black Sea coast.

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