Publication Date


Document Type


First Advisor

King, Richard B.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Blanding’s Turtles (IUCN Endangered) are long-lived reptiles with delayed sexual maturity. Anthropogenic landscape changes have increased threats to juvenile turtles, resulting in unnaturally low recruitment. Head-starting has become a popular conservation strategy that aims to increase juvenile recruitment by avoiding the increased predation of the vulnerable nest and hatchling age-class. However, there is still debate about whether or not it is an effective management tool. Assessments of head-starting are becoming more prevalent, but long-term studies are needed to critically evaluate the success of such interventions. In particular, information is needed on how head-starts fare compared to wild-born turtles. The Lake County Forest Preserve District (LCFPD) in northeastern Illinois initiated a long-term capture-mark-recapture (CMR) project in 2004. As of 2018, 127 wild-born juvenile turtles had been captured (59 of which had been captured in multiple years) and 148 adult turtles had been captured (116 of which had been recaptured in multiple years). Since 2010, LCFPD has released 491 head-started turtles during the year following hatching, 138 of which have been recaptured during successive years. I used van Bertalanffy growth analysis to compare growth trajectories and Cormack-Jolly-Seber (CJS) modelling techniques to compare survival rates of wild-born and head-started turtles. At release, head-started turtles were about the size of 2-year old wild-born turtles and grew in parallel to their wild-born counterparts. The top ranked survival models demonstrated that survival increased with age for both wild-born (71%-98%) and head-started turtles (63-90%) with overlapping confidence intervals. These results suggest that head-started juveniles perform similarly to like-aged wild-born juveniles despite head-starts having attained greater body size. I estimated adult survival to be 95% with an environmental variance of 0.0011. Although the success of head-starting cannot be fully assessed until turtles are recruited into the adult population and successfully reproduce, patterns of head-start growth and survival provide positive intermediate measures of success. My estimation of juvenile and adult survival, along with other demographic information from this population, will provide for more accurate population projections that will aid in evaluating conservation strategies for this population and potentially for Blanding’s Turtles elsewhere.


59 pages




Northern Illinois University

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