Parameters of breeding were studied in seven rookeries in the agricultural landscape of eastern Poland. Within foraging territories near colonies, proportions of environmental components were defined, and avoided and preferred types of crops were distinguished. The mean clutch size, mean number of hatchlings and mean number of fledglings per successful brood did not differ between colonies and did not depend on colony size. In contrast, total losses at the stage of egg incubation and feeding chicks, the mean number of fledglings calculated per breeding pair and the overall breeding success were different. Foraging territories around each colony usually had different proportions of preferred and avoided crops. Breeding success depended positively on the area of preferred crops: spring cereals and meadows and pastures. Breeding success seemed to decrease with the area covered by avoided crops and winter crops, but the relationship was not significant. The area of spring cereals was positively but not significantly correlated with the mean number of fledglings.