Group stability – a pilot study of a wisent herd of Bieszczady Mountains

Abstract

To assess a multiannual dynamics of group structure/composition in a wisent herd inhabiting Bieszczady Mountains, compared were records of presence of characteristic individuals with deformed/ malformed/ broken horns. Selected were 14 observations of possibly large groups (over 10 individuals), representing in total 388 individual records, obtained between 2008 – 2015, within the range of an eastern subpopulation of wisents in this region (so called “Tworylne” herd). Estimated was the total number of individuals in a group, proportion of bulls, cows and young up to 1 year. Among bulls identified were three age classes: 2 years, 3–5 years, 6+ years. Among cows distinguished were young females in their second year of life and older (3+). The most variable was the presence of bulls. The presence of cows was more stable, however even in case of a cow observed every year between 2008 – 2014, there were several gaps in her presence in the herd. High irregularity of group structure and composition, excludes purposefulness of performing the population census for wisent herds living in fairly natural conditions just once a year. Population census should take place in late  winter/early spring, during the period of highest stability of mixed groups, and be repeated during the rut when adult bulls temporarily join the herd.