Bisoniana 110. Free ranging European bison in Borecka Forest

Abstract

This paper presents the history, herd structure, distribution and habitat preference of the free ranging herd of European bison Bison bonasus (Linnaeus, 1758) in Borecka Forest, north-east Poland. Herd numbers fluctuated between 48 and 71 individuals from 1976 - 1991 through population regulation by sport shooting and removal of culls. During the snow free period the bison were distributed in a 8700 ha part of the forest area with an actual density of 6 - 8 individuals per 1000 ha. The coefficient of birth was 18.2% on average and the mortality coefficient was 4.3%. The structure of the population varied because animals were introduced, and removed by hunting. The average size of mixed groups was 11.0 +/- 10.6 individuals and the groups of bulls averaged 1.44 +/- 0.6 animals. Solitary bulls compriseed 68.5% of observations. Mixed groups formed one large aggregation around supplemental feeding sites in winter; adult bulls wandered separately. Bison preferred deciduous forests (96.7% of all forest observations) especially stands older than 20 years (87.5%) and occasionally thickets (12.5%). To a large degree they used open areas as feeding grounds (37%) although they preferred the forest (63%). We compared the basic data of the European bison's ecology in Borecka and Bialowieza Forests and found that group type, size, and spatial structure were characteristic features of this species. The bison showed similar population trends in different environments of lowland forests but their use of forest types varied according to diversity and food abundance.