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

Abstract

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.

Blanding's Turtle Demography and Population Viability

“…Researchers determined sex of adults by observing the concavity of the plastron (Graham and Doyle 1979). Researchers equipped a subset of adult Blanding's turtles, mostly females, with radiotransmitters, facilitating collection of reproductive data (Thompson et al 2020).…”

“…This site consists of 215 ha of high-quality coastal wetland habitat along Lake Michigan and is part of the Chiwaukee Illinois Beach Lake Plain, recognized among Wetlands of International Significance (https://rsis.ramsar.org/, January 2021). It is managed by the Lake County Forest Preserve District, Wisconsin Department of Natural Resources, and The Nature Conservancy, and has been the focus of efforts aimed at promoting Blanding's turtle recruitment, survival, and habitat quality, including prescribed fire, mechanical and chemical treatment of invasive plants, turtle head-starting, and mesopredator removal (Urbanek et al 2016;Thompson et al 2020). Supplemental information comes from shorter term (2017-2019) Blanding's turtle monitoring at Illinois Beach State Park (IBSP), an adjacent 1,680-ha coastal wetland complex immediately south of SBCP, and from the work of researchers elsewhere.…”

“…We computed environmental variance in the proportion of females reproducing by subtracting mean annual binomial variance from the among-year variance following Akçakaya (2002). We obtained data on number of eggs per clutch from 120 clutches included in the Lake County head-starting program from 2008 to 2018 (Thompson et al 2020). We estimated environmental variance in clutch size (¼ among-year variance) from variance components analysis computed using the restricted maximum likelihood method in IBM SPSS 25 with year and female ID as random factors.…”

“…Rates of clutch failure were obtained by using telemetry to observe nesting at SBCP and IBSP coupled with follow-up monitoring to determine nest outcome (depredated, destruction by other causes, undisturbed; Urbanek et al 2016). Hatch failure was estimated from the Lake County Forest Preserve District head-starting program (Thompson et al 2020) based on eggs incubated from 2008 to 2018. Rates of posthatch mortality were obtained from Kastle et al (in press), who used telemetry to monitor 82 hatchlings for up to 88 d at sites in northern Illinois and southern Wisconsin, including SBCP, and then extrapolated mortality from hatching through resumption of spring activity.…”

“…Available information on Blanding's turtle demography has been used in population viability analyses (PVA) to assess impacts of road mortality (Beaudry et al 2008), alternative management and urban development scenarios (Dillon Consulting Limited 2013), and headstarting (in which eggs are collected and hatchlings are reared in captivity to minimize mortality during vulnerable early life stages) as a management strategy (Buhlmann et al 2015;Thompson et al 2020). In general, PVA makes use of mathematical models to generate future projections of population dynamics (Morris and Doak 2002).…”