Rafał Bobrek, Tomasz Wilk, Aleksandra Pępkowska-Król
Ornis Polonica 2018, 59: 89–106
https://doi.org/10.12657/ornis.2018.2.0
Abstract: The paper presents the occurrence of the Great Cormorant Phalacrocorax carbo at 12 main water reservoirs in the Polish Carpathians from August to March and the parameters of spring and autumn migration of the species in the area. Additionally, the two survey methods estimating the dynamics of passage were compared: the visual monitoring of migration at 19 selected points, and counts of birds gathering on water bodies. Both methods indicate that Cormorants were more numerous in the western and central part of the studied area. Spring peak of migration took place in mid and late March. On average 4.9 ind. per 10 h of observation were noted in a single point in spring, with the mean and maximum flock size of 13.4 ind. (SD=19.5; Me=5) and 80 ind., respectively. A total of 97% of Cormorants migrated in spring in the N or NE direction. Autumn migration was more intense – on average 5.8 ind. per 10 h of observation, with mean and maximum flock size in autumn of 14.1 ind. (SD=17.4, Me=7) and 80 ind., respectively. The two migration peaks were noted – in mid October and early November, and 84% of birds migrated in the S or SW direction. The lowest numbers of Cormorants (ca 160 ind.) were noted on reservoirs in August, and the highest numbers (nearly 880 ind.) in October. The winter minimum (ca 210 ind.) occurred in February and coincided with the largest ice cover. The number of Cormorants decreased with increasing ice cover extent on the reservoirs. The period of marked migration and wintering of Cormorants in the studied region covered ca 7 months, from late September to early April. Both methods of assessing the dynamics of migration produced similar results in terms of timing of minimum and peak of the passage. Monthly counts of bird concentrations on reservoirs, however, did not detect short-term changes in the migration intensity, which were registered at observation points. Therefore, if only the Cormorant migration is spatially concentrated, the direct visual monitoring of passage valuably supplements the data collected during counts on water bodies.
Keywords: dam reservoirs, Great Cormorant Phalacrocorax carbo, monitoring of migration, mountains, visible migration, winter counts
