Maintaining biologically functional and compatible social groups is a primary welfare concern for captive animals. The aim of this study was to determine the effect of a pack size change -due to a new yearling- on the daily activity, use of space and inter-individual distance in a mated pair of Iberian wolves ( Canis lupus signatus ) housed at the Barcelona Zoo. Multifocal sampling methods were used for data collection, and instantaneous scans were made at 15-min intervals during 10-h sessions. 432 sampling points were balanced for the daily periods – morning, midday, and afternoon - for two different phases: dyad and triad phase. The subjects studied during the dyad phase - from April to May 1999 - were the mated pair. For the triad phase - from April to May 2000 – we studied the mated pair and the new yearling. When comparing these two study phases, there were statistically significant differences for the daily activity and the use of space. The mated pair used the space more homogenously during the triad phase. In the same phase, the inter-individual distance between the mated pair was statistically significantly closer in the morning and in the midday. The mated pair also showed individualized results for their daily activity, use of space and inter-individual proximity during the triad phase. Increasing understanding about the pack size enables the improvement of management to provide wolf packs with the most appropriate social environments.