First Year Survival of Hatchling Eastern Box Turtles (Terrapene carolina carolina) at Their Northern Range Limit in Michigan's Lower Peninsula
As adult turtle mortality increases as a result of anthropogenic threats, understanding the survival of younger age classes may help mitigate population declines. We radiotracked hatchling Eastern Box Turtles (Terrapene carolina carolina) through the first year of life in a Michigan population, located on the northern edge of their range. We monitored 60 hatchlings for between 2 and 333 d and estimated annual survival using known-fate survival estimates. From 2013 to 2015, 14 hatchlings (23%) were depredated, 19 hatchlings (32%) died because of exposure, and 2 hatchlings (3%) were crushed by motor vehicles. Survival decreased through the first year of life with a drop in survival probability from nest emergence in the autumn, before it reached 50% during overwintering (day 50 = 0.503; SE = 0.067), then again decreased with spring emergence and ending with 0% survival (day 333 = 0.0). Hatchlings that emerged in September survived up to 107 d longer than hatchlings that emerged in October, and larger hatchlings had a significantly higher probability of survival over smaller individuals. No small hatchlings survived through overwintering, whereas large hatchlings had a 0.82 (±0.095 SE) survival probability 228 d posthatching. Threats to a species survival at the limits of its range are often different from those faced by populations centrally located within the range. Thus, studies should be conducted across the Eastern Box Turtle's range to determine how survival probabilities vary in populations experiencing different environmental conditions.ABSTRACT
(A) A hatchling Eastern Box Turtle shortly after emerging from the nest in Manistee National Forest. (B) A hatchling Eastern Box Turtle fitted with a 0.5-g radiotransmitter on the posterior of the carapace using two-part epoxy.
Kaplan–Meier estimation of annual survival for Eastern Box Turtle hatchlings in Manistee National Forest for the 2013–2015 cohorts. Dashed lines indicate 95% confidence intervals with addition signs (+) representing dates when hatchlings were censored from study. Day 1 represents earliest hatchling emergence for the study period (22 August).
Kaplan–Meier estimations of annual survival for Eastern Box Turtle hatchlings in Manistee National Forest separated by cohort year. Day 1 represents the first date of hatchling emergence per study year.
Kaplan–Meier estimations of annual survival for Eastern Box Turtle hatchlings in Manistee National Forest for the 2013–2015 cohorts separated by month of emergence. Day 1 represents the date of first hatchling emergence in each month.
Kaplan–Meier estimations of annual survival of Eastern Box Turtle hatchlings in Manistee National Forest for the 2013—2015 cohorts separated by mass class (small 5.5–7.0 g, medium 7.1–8.6 g, and large 8.7–10.2 g). Day 1 represents the first date of hatchling emergence for each mass class.
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