Movements of European bison (Bison bonasus) beyond the Bialowieza Forest (NE Poland): range expansion or partial migrations?

The European bison is the largest terrestrial mammal in Europe. After extinction in the wild at the beginning of the twentieth century, it was re-introduced to Bialowieza Forest and other woodlands in Eastern Europe. In this paper, we analysed the movements of European bison beyond the continuous woodlands of the Bialowieza Forest (NE Poland) between 1964 and 2010. In total, 1,117 direct observations of bison were collected. The number of males moving out of the forest fluctuated during the study period, whilst the number of females steadily increased. The number of male observations outside of the forest per annum was dependent on the population size and snow depth, whilst the number of cows in mixed groups moving outside of the forest was correlated with the population size only. Males were observed mainly alone (50 % of observations) or in small groups of two to three individuals (25 %); however, distribution of group size differed from those observed in the population. There was a significant difference between the direction of movement of males and females out of the forest-males moved mainly west and southwest, whilst females moved to the north. This was also significantly different from the expected movement direction. The mean distance of bison observations from the forest border was 1.8 ± 0.13 km and did not differ significantly between sexes. After 1990, males were observed significantly farther away from the forest (2.2 km) than in the previous years (0.9 km). Most observations (94 % of bulls and 93 % of cows) were up to 5 km from the forest edge. The range of bison in the vicinity of the Bialowieza Forest was strictly seasonal. Most observations (78 % in males and 88 % in females) were recorded from November to April. Increasing utilisation of areas beyond the forest habitats may be driven by different factors but most probably it is related to range expansion and the bison's preference for open habitats. The strong seasonal pattern of bison movements indicate that the partial seasonal migrations were initiated in the Bialowieza population.

Liver histological structure in adult European bison. Bison bonasus (Linnaeus, 1758).

The histological structure of the liver in 12 European bison, 2-8 years old, was presented. The study of the hepatic lobule showed that in Bison bonasus there were no connective septa around the hepatic lobules. On the hepatic lobule territory, solitary bile ducts, respectively solitary arterioles, were sometimes observed. Every one of these vessels was isolated from the hepatic parenchyma by thick coats of collagen. In the adventitia of the hepatic sublobar vessels, capillaries of the vasa vasorum system were found. The thick capsule of Glisson presented an outer part lacking in blood vessels and an inner part vascularised with arterioles and capillaries originating from the subcapsular portal tracts. The ligament insertion in the liver parenchyma was described.