Post‐release survival of captive‐reared Allegheny woodrats

• Published in: Animal conservation 2015-04, Vol.18 (2), p.186-195
• Main Authors: Blythe, R. M, Smyser, T. J, Johnson, S. A, Swihart, R. K
• Format: Article
• Language: English
• Subjects: Allegheny woodrat; Behavior; body condition; breeding; captive breeding; Cox proportional hazards; environmental enrichment; Kaplan-Meier; monitoring; Neotoma; population; radio telemetry; rearing; sampling; soft release; survival; survival rate; translocation; wild animals
• ISSN: 1367-9430; 1469-1795
• DOI: 10.1111/acv.12158

Captive breeding to augment wild animal populations is an important tool in the recovery of imperiled species, but low post‐release survival and substantial program expenses require methodologies that maximize utility. We evaluated post‐release survival of captive‐reared Allegheny woodrats (Neotoma magister) introduced into a declining metapopulation in southern Indiana. We hard‐released 16 captive‐reared woodrats in 2011 and soft‐released 14 woodrats in 2012, while monitoring parallel samples of 16 and 17 wild‐born individuals in each year, respectively. We obtained Kaplan–Meier estimates of survivorship for both groups and used Cox proportional hazards regression to estimate the association between survival and rearing environment (wild or captive), release strategy, sex, body condition and age at release. We quantified movement patterns and related the results of survival models to behavioral tendencies. Survivorship of wild‐born individuals was consistently higher than captive‐reared individuals. Patterns of survival were best explained by rearing environment and its interaction with time, although disparities in survival between wild‐born and captive‐reared animals decreased over time. Higher mortality among captive‐reared individuals may have been due to more exploratory behavior, as captive‐reared woodrats used more dens and traveled farther among successive relocations than wild‐born conspecifics. Soft‐released individuals had higher initial survival rates and tended to choose dens similar to those of wild individuals, providing evidence that this strategy eased the transition to a wild environment. We recommend future programs use soft‐release techniques but also explore other pre‐release preparatory strategies such as anti‐predator conditioning and environmental enrichment to increase survival.