Factors affecting the variability in home range size and distribution in European bison in the Polish and Belarussian parts of the Bialowieza Forest

The size and spatial distribution of home ranges of the European bison Bison. bonasus (Linnaeus, 1758) in the Polish and Belarussian parts of the Bialowieza Forest were studied in the years 1993-1998. In this period, 28 bison (18 males and 10 females) aged 4-10 years, including 20 (15, 5) from the Polish part of the Bialowieza Forest and 8 (3, 5) from the Belarussian Dart, were radio-collared. The mean size of winter home ranges of bulls was 10.7 km(2) (range 0.8-32.2, n = 25) while that of cows was 7.9 km(2) (range 0.7-34.3, n = 15), difference between the sexes not being significant. The size of winter home ranges was significantly correlated with the duration of snow cover and with the mean daily temperature in winter (R-2 = 0.311, p = 0.001). Long-lasting snow cover and low temperatures significantly limited bison mobility in the forest. In the snow-free season, the mean size of home ranges of bulls was 69.5 km(2) (range 29-151.6) and that of cows was 68.8 km(2) (range 45.4-97.5), the difference not being statistically significant. The size of bulls' home ranges in the snow-free period was related to their age. The mean size of home ranges of younger adult bulls was 44.02 km(2), being significantly smaller than the ranges of older adult bulls (84.3 km(2)) and cows. European bison used their ranges unevenly and showed individual spatial fidelity in subsequent years. Home ranges of the European bison of both sexes were not defended and overlapped extensively. Food abundance of remarkably diverse habitats (forest, meadows) had a significant effect on the size of bison home ranges. In August-October, home ranges of cows from the Polish populations penetrating the forest averaged 45.5 km(2) and were significantly larger than the ranges of cows from the Belarussian population foraging on meadows (24.3 km(2)).