Mortality and spatial behaviour of farmed red deer after hard reintroduction

Red deer, Cervus elaphus, is native to Europe and is one of the most frequently managed ungulate species. Reintroduction programmes often use farmed animals because they require less effort than live-captured wild animals, but farmed animals may struggle to acclimatise to life in the wild. We conducted this study in central Croatia from 2017 to 2024 and analysed the post-release spatial behaviour of 16 farmed red deer fitted with GPS collars (10 ♀ and six ♂) after a hard release (animals released from the trailer without acclimated period). Overall mortality reached 69% (11 animals) and poaching mortality showed a sex bias, with 100% mortality in males and 40% in females. Females had an average home range (minimum convex polygon, 95%) of 27.4 km2 and males 98.4 km2. We found no significant sex difference in the home range establishment period, defined as the time until stabilisation of post-release space use, although sample size was small (six out of 10 females, two out of six males). The high mortality rate supports that farmed deer struggle to adapt to the wild. Future work should evaluate if success is higher if using wild deer for reintroductions and evaluate soft release (animals released from the enclosure after acclimated period).