Zarys dynamiki liczebności szponiastych Accipitriformes i sokołowych falconiformes w okresie pozalęgowym w krajobrazie rolniczym pod Siedlcami

In the periods 4 November 2011 to 15 March 2012 and 14 August to 21 November 2012, 11 surveys of birds of prey Accipitriformes and Falconiformes were conducted in the Zbuczyn area (56.3 square km) near Siedlce (E. Poland). Only stationary birds (resting or foraging) are included, without those flying high on migration. In the postbreeding season 2011-2012, a total of 11 species of the two orders of birds of prey were noted, varying from one to seven species and from eight to 57 individuals per survey. In total 314 birds were recorded. The most abundant species was the Buzzard Buteo buteo (N=265), contributing to 84.4% of all birds of prey. Buzzards were most abundant in the period of early autumn migration, with a highest density of 12.0 ind./10 square km of open area (grassland and cropland) and a lowest density in the early winter and late winter periods (1.8 ind./10 square km in each). Over the whole winter period (15 December – 17 February), the mean density was 3.0 ind./10 square km. In the late autumn period (November) of the two seasons (2011 and 2012), numbers of Buzzards did not differ markedly, varying from 19 to 25 individuals. Numbers of other species were much lower: Marsh Harrier Circus aeruginosus (N=17), Kestrel Falco tinnunculus (N=10); Rough-legged Buzzard Buteo lagopus (N=6), and Montagu’s Harrier Circus pygargus (N=5). Numbers of the remaining species did not exceed 4 individuals over the study period. The assemblage of birds of prey near Siedlce had the same species composition and dominance structure (Re=79) as that near Hajnówka monitored as the same time (Pugacewicz 2012). But their numbers were higher near Hajnówka. In total, 432 birds were recorded (9.4 ind./10 square km/survey), as compared with 314 birds (6.3 ind./10 square km/survey) near Siedlce. The densities of buzzards near Siedlce were lower than near Hajnówka. This was likely due to a lower available food supply, the proportion of open habitats being similar in the two areas. The pattern of changes in numbers of buzzards was similar in the two areas.