Eleven calves from the European bison breeding centres of Białowieża National Park (Poland) were observed during the first 3 months of life to investigate their integration patterns into a group. Spatial relations of the calf with other bison in a group were reflected in the distance to group members of various categories and in the extent to which individuals synchronized their behaviour. Data on changes in the calf’s activity pattern provided information on the transformation in feeding habits. Three main phases were identified in the early period of European bison’s life: (1) establishment of mother-infant bond, (2) incorporation of a calf into a calf subgroup, and (3) integration of the calf into the whole group. Incorporation of the calf into a herd started in week 2. The pattern of calf’s integration was determined by transformation of its activity pattern. At first similarity of activity patterns among calves resulted in synchronization of their behaviour and proximate company. In the next phase, the change in the primary source of nutrition from nursing to grazing and gradual alteration of activity pattern towards an adult’s one led to non-specific spatial relations with group members and integration of the calf into the herd.