Acclimatisation duration, not just release type, drives post‐release settlement in a large‐scale carnivore reintroduction programme

Abstract Although animal reintroductions are a cornerstone of conservation practice, the effectiveness of distinct release strategies remains debated. Soft‐release, involving pre‐release acclimatisation in enclosures, is often assumed to improve outcomes over hard‐release, but evidence is inconsistent. We propose that variation in acclimatisation duration, rather than release type alone, may explain these discrepancies. Using GPS telemetry data from the extensive Iberian lynx ( Lynx pardinus ) reintroduction programme—spanning multiple sites across its distribution range and individuals of varying ages, sexes and origins—we evaluated how acclimatisation period length and release strategy influence post‐release movement and settlement. We found that prolonged acclimatisation significantly reduced long exploratory movements and increased the probability of settling within the targeted area, while release type alone had no significant effect. This demonstrates that time spent in the enclosure, rather than the use of soft‐release per se, drives early‐stage reintroduction effectiveness. The greatest benefits were achieved after approximately 6 weeks of acclimatisation, marking the point at which settlement probability exceeded 50% for all groups. Beyond this threshold, additional time in the enclosure provided diminishing returns, offering a practical benchmark for future releases. Synthesis and applications . Our study highlights that when acclimatisation periods are too short, the substantial economic and logistical investment in soft‐release protocols may fail to deliver the expected conservation gains. Therefore, defining evidence‐based acclimatisation periods that are long enough to promote settlement, yet compatible with logistical constraints, may provide valuable guidance for reintroduction planning. More broadly, our findings identify acclimatisation duration as a promising factor to evaluate in other carnivore reintroduction programmes, which may likewise benefit from incorporating such assessments into their planning and design.