Benefits of Head-starting for Blanding's Turtle Size Distributions and Recruitment

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.