Population Viability Analysis and The Role of Head-Starting for a Northern Illinois Blanding’s Turtle Population

The Blanding’s Turtle (Emydoidea blandingii) is a long-lived species that was once common in the prairies and wetlands of northern Illinois, but now only occurs in scattered populations. To aid the recovery of Blanding’s Turtle populations the Forest Preserve District of DuPage County maintains a head-starting and release program. We previously conducted trapping and analysis at the main release site to determine basic demographic parameters under the current head-starting program. We found moderately high head-start survival, fairly high adult female survival, and an increasing population size suggesting that head-starting is working as a conservation strategy. To investigate future population trajectory and the outcome of continued head-starting we conducted a population viability analysis (PVA) in the program VORTEX incorporating updated demographic data from surveys in 2018. Updated models indicate moderately high head-start survival that may increase with body size. Though population size continues to increase, the PVA indicates some form of ongoing management is necessary to avoid a negative stochastic growth rate. Ceasing head-starting could result in extinction (within 100 years) if no natural recruitment is occurring. Head-starting 50 eggs/year did not result in extinction for any of the scenarios modelled, and head-starting 100 eggs/year would maintain or increase population size. Head-starting 200 eggs/year would increase population size even if juvenile mortality is higher than current estimates indicate. Alternatively, maintaining high natural age 0-1 survival would increase growth rate, but may be difficult because current egg and hatchling mortality are unknown (but likely high). Maintaining high adult survival will be important regardless of other management practices. We conclude that for this population the best management strategy is to head-start at least 100 eggs/year until the threat of road mortality can be mitigated and other management can demonstrate adequate natural recruitment.