Abstract
ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 40:17-29 (2019) - DOI: https://doi.org/10.3354/esr00978 Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release Thomas A. Radzio1,*, Nicholas J. Blase1, James A. Cox2, David K. Delaney3, Michael P. O’Connor1 1Department of Biodiversity, Earth, and Environmental Science, Drexel University, Philadelphia, Pennsylvania 19104, USA 2Tall Timbers Research Station and Land Conservancy, Tallahassee, Florida 32312, USA 3United States Army Construction Engineering Research Laboratory, Champaign, Illinois 61822, USA *Corresponding author: tomradzio@hotmail.com ABSTRACT: Captive rearing represents a vital component of many conservation and research programs. However, captive animals can exhibit unnatural behaviors and experience high predation following release, which can limit reintroduction success and the inferential value of studies that use released animals. Soft-release measures (e.g. penning) can acclimate individuals and limit interactions with predators but can also require considerable resources. We reared hatchling gopher tortoises Gopherus polyphemus in the laboratory for physiology experiments and subsequently hard-released them as yearlings to assess the efficacy of this low-cost release method and to explore possible captivity effects on tortoise behavior, growth, and survivorship. Hard-released yearlings exhibited limited dispersal; most constructed burrows soon after release, and, like wild juveniles, exhibited a preference for burrowing under deadwood. Video observations at burrows indicated natural behavior, including overnighting in burrows, extensive basking directly in front of burrows, and limited time away from these important refugia. Basking tortoises responded to simulated predator approach by rapidly entering burrows, with flight initiation distances and hiding times equivalent or similar to those of wild individuals. Survivorship was comparable to that of soft-released juveniles, but growth was slightly lower than expected based on observations of wild tortoises at the site, possibly reflecting performance immediately following release. Our findings indicate that captive-reared juvenile gopher tortoises respond well to hard release and exhibit natural attributes required to thrive in the wild. Moreover, studies of released juveniles can yield valuable insights into the ecology of a life stage that is poorly understood in most chelonians. KEY WORDS: Gopherus polyphemus · Turtle · Conservation · Headstarting · Antipredatorbehavior · Thermal ecology Full text in pdf format Correction PreviousNextCite this article as: Radzio TA, Blase NJ, Cox JA, Delaney DK, O’Connor MP (2019) Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release. Endang Species Res 40:17-29. https://doi.org/10.3354/esr00978 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 40. Online publication date: September 19, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.
Highlights
Maintaining animals in captivity represents a vital component of many conservation and research programs (Swimmer et al 2005, Crone et al 2007, Griffiths & Pavajeau 2008)
At least 14 of 30 (≥47%) radio-transmittered tortoises started constructing a burrow within 2 d of hard release; ≥22 (≥73%) initiated a burrow within 4 d; and ≥27 (≥90%) had done so within 13 d (Fig. 1)
Consistent with wild individuals, most released yearlings spent the majority of their time in or near burrows but basked extensively on burrow aprons (Wilson et al 1994, Pike & Grosse 2006, Radzio 2017, Radzio & O’Connor 2017)
Summary
Maintaining animals in captivity represents a vital component of many conservation and research programs (Swimmer et al 2005, Crone et al 2007, Griffiths & Pavajeau 2008). Chelonians are declining worldwide owing to a variety of threats (Buhlmann et al 2009, Böhm et al 2013, Lovich et al 2018), and for some critically endangered species, captive breeding may represent a necessary action to reestablish viable wild populations (Milinkovitch et al 2013, Spencer et al 2017) This approach can work, but success may require decades of repeated effort (Milinkovitch et al 2013), in part due to life history traits such as low survival of small juveniles and delayed sexual maturity (Congdon & Gibbons 1990, Heppell et al 1996). Short-term studies of behavior, growth, and survivorship can provide important information for intermediate assessment and calibration of release efforts (Pedrono & Sarovy 2000, Lepeigneul et al 2014, Tuberville et al 2015, Spencer et al 2017)
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