Reintroduction has become an increasingly common approach for conservation of endangered species. However, reintroductions can be logistically challenging and expensive, with uncertain outcomes, making it a priority to establish effective post-release monitoring techniques. In north-eastern Argentina, collared peccaries (Pecari tajacu) have been locally extinct for over 50 years. As part of a multi-species rewilding project, seven captive-born collared peccaries were released into Ibera Nature Reserve in 2015. Using radio telemetry and camera traps, we evaluated temporal changes in the peccaries’ post-release activity budget and activity patterns as indicators of reintroduction progress and potential establishment into the new area. Collared peccaries changed their activity budget and peak periods of activity towards a more natural pattern a year after release, from 30% to 49% foraging time and 18% to 2% traveling time. Our results highlight the potential of using activity budget assessments and camera trapping data to monitor the progress of introduced individuals and inform managers’ decision-making process after reintroductions.