Head‐starting is a widely used turtle conservation measure but its effectiveness is incompletely known. We evaluated the success of 2 long‐term Blanding's turtle (Emydoidea blandingii) head‐starting programs in northeastern Illinois, USA, focusing on the effect that head‐starting has on turtle population body‐size distributions and whether head‐started turtles are successfully recruited as reproductive adults. From 1994 to 2017, we collected and incubated eggs from wild females and reared hatchlings for release back into 2 source populations in DuPage and Lake counties, Illinois. Releases occurred annually for 21‐ and 11‐year spans (~1,400 and 800 releases, respectively). We found that head‐starting resulted in significant shifts in Blanding's turtle population body‐size distributions. Prior to intervention, size distributions were strongly skewed toward large adults at both sites, a pattern sometimes interpreted as arising from elevated egg and hatchling mortality and a lack of juvenile recruitment. Currently, population body‐size distributions include a wide range of juvenile and adult size turtles. Importantly, head‐starts have begun reproducing in the 21‐year program and are approaching adult size in the 11‐year program. Blanding's turtle head‐starting shows promise for increasing recruitment in existing populations while threat mitigation is implemented. © 2020 The Wildlife Society.

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Declining reptilian populations has been a growing concern over the last couple of decades. One such declining species of concern, the Blanding's turtle Emydoidea blandingii, occurs as isolated populations in North American prairie-wetlands and is at risk of extirpation due to habitat loss and fragmentation, and increased predator (e.g. racoons, coyotes) populations due to supplemented resources in urban environments. To help mitigate declining populations, wildlife managers have invested in the conservation of this species through head-starting (i.e. reared in ex situ) and juvenile release programs to augment wild Blanding's turtle populations. However, much of their spatial and winter/thermal ecology is understudied, and data for juveniles, and juveniles reared ex situ is especially scarce, yet this information is imperative to understanding shortfalls and improving head-starting efforts in the future. In spring 2016 (RR 2016 ) and 2017 (RR 2017 ) we released a cohort (n = 12 each year) of head-started juvenile Blanding's turtles equipped with radio transmitters and temperature dataloggers into a prairie-wetland in the greater Chicago region, North America. Using ground-based radio telemetry, we determined seasonal movement areas (SMAs; spring, summer and fall) and annual home ranges (AHRs) for both RR 2016 and RR 2017 cohorts via kernel density (KD) estimates. We also investigated the thermal characteristics of overwintering for both juvenile cohorts. We found that SMAs for the RR 2016 cohort, but not for the RR 2017 cohort, significantly differed across seasons for most SMA estimators. We also found that juveniles in both cohorts not only survived overwintering, but also displayed similar overwintering phenology (i.e. initiation: October-November; termination: April) and temperature variation as Blanding's turtles adults in other studies. Overall, our results indicate that head-started juvenile Blanding's turtles may be able to acclimatize quickly to their natural environment post-release. Our study provides evidence to the efficacy of well-developed head-starting programs that aim to augment and preserve imperiled turtle populations.