The "trap, spay/neuter, and release" programs to manage unowned free-roaming cat populations are diffused worldwide and they are largely advised even in countries where the suppression of unowned cats is enforced by law. Despite the massive neutering campaigns in the world, there is little information on the influence of neutering on individual cat behaviour, as well as on the social structure of cat colonies. The aim of this study is to verify such effects. Before neutering, the group consisted of 17 free-roaming domestic cats, who were totally unrestrained. After neutering it consisted of 16 individuals. Data on the outcomes of aggressive, submissive, affiliative, and territorial behaviour were collected, using classic ethological methods ("focal animal", "all occurrences", and "1/0" sampling methods) (735 h of observation before and 537 h after neutering). The dominance hierarchy did not change after neutering. On the other hand, the frequency of aggressive, territorial behaviour as well as proximity among individuals decreased significantly. Affiliative behaviour has been observed among neutered adult males that never performed it before neutering. The results of this study suggest that, after neutering: (i) The group of free-ranging cats was stable over time; (ii) the hierarchical structure of the cat social group did not change; (iii) the general level of activity, decreased; (iv) urine spraying marking behaviour almost disappeared; (v) the level of social proximity among group members decreased, although it tended to increase in some male-male dyads. The most obvious effect of neutering, detected on individual behaviour, was that cats were less active.
Keywords: activity level; neutering; social behaviour; unowned domestic cats.