Effect of age class on the survivorship and spatial movement patterns of headstarted Texas horned lizards soft‐released into an urban population

Texas horned lizards ( Phrynosoma cornutum ) have experienced population declines and localized extirpations throughout their historical range, largely due to anthropogenic habitat loss. Consequently, there is broad interest in reinforcing persisting natural and urban populations and reintroducing the species into previously occupied environments. To this end, headstart programs have been established that temporarily rear young wild‐sourced or captive‐bred hatchlings in captivity before their release into the wild. To understand the effect of age on short‐term reintroduction objectives, we implemented a 2‐year radio‐telemetry study (April 2023–October 2024) on an urban wildlife reserve at Tinker Air Force Base, Oklahoma, USA. We compared the spatial movement patterns and survivorship of 2 soft‐released cohorts of headstarted lizards, raised either to juvenile or adult age, to resident lizards of the corresponding age class. The headstarted adult cohort ( n = 16) exhibited lower daily movement distances, smaller home ranges, and lower survivorship compared to resident adults ( n = 19). However, despite these differences, the majority of headstarted adults survived approximately 3 months before a mass predation event, and the 4 surviving adults successfully underwent and survived brumation. In contrast, we did not observe significant differences in spatial movement metrics between the headstarted juvenile cohort ( n = 8) and the resident juveniles ( n = 9). Although we did not detect a difference in survivorship between the headstarted and resident juveniles, the statistical power of our survival analysis was limited by small sample size. Nearly all recorded mortality was attributed to predation; notably, nearly a third involved unusual decapitations. Our findings highlight the necessity of post‐release monitoring and suggest that headstarting Texas horned lizards to juvenile age before reintroduction may serve as a worthwhile supplement to the current method of releasing headstarted hatchlings before brumation. For threatened urban populations, future reintroduction efforts should be coupled with predator management strategies to mitigate mortality risk.