Bisoniana LXVII. Dynamics and structure of the European bison population in the Białowieża Primeval Forest

Abstract

The paper discusses population dynamics, sex and age structure, group composition and size, density and spatial structure of a free- living population of European bison Bison bonasus ( L i n n a e u s , 1758) in the Białowieża Primeval Forest. The study covers the period from the sta rt of free breeding in 1952 up to the end in 1973. From 1968—1970 detailed studies were made on the population formed by tha t time with a total of 2400 observations. The b irth coefficient for the period from 1960—1973 averaged 18.5%. The high fecundity coef? ficient (70%) during the initial period of the herd’s development dropped (54%) during the final study years. Sex ratio at birth did no t differ significantly from 1:1 with 316 (161 males, 155 females) calves born. Mortality coefficient was low (3%). Significantly higher mortality was observed afnong males than females. Maximum mortality was found in the group of calves up to one year old (23%). The area in which the European bison herd lived enlarged with increase in population numbers up to 1966, after which only density rose. Habitat preferences influenced distribution of groups of bison during the sum? mer period, the animals most often wandering in mixed deciduous forest (24% of encounters) and deciduous forest (18.5%), and least often in coniferous forests (2%). Feeding bison were often encountered in clearings, meadows and cultivated fields (47% of all encounters). Mixed groups consisting of bison of both sexes in different age classes and bull groups were distinguished. The composition of mixed groups altered depending on the season. During the ru tting period (Aug.-Sept.) the majority of the mixed groups included adult bulls, and the number of these bulls in the group increased twofold. Mixed groups averaged 12 (1—38) animals, and bull groups averaged 2 (1—7). During the w inter period the bison formed large aggregations around feeding places (maximum 97 animals). Also discussed is a comparison of the study population of European bison with the population living in the Biało? wieża Primeval Forest in the 19th century and with the American bison, Bison bison