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Endangered Species Research

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ESR 5:21-27 (2008)  -  DOI:

Assessing age in the desert tortoise Gopherus agassizii: testing skeletochronology with individuals of known age

Amanda J. Curtin1,4, George R. Zug2,*, Philip A. Medica3, James R. Spotila1

1Department of Bioscience and Biotechnology, Drexel University, 3141 Chestnut St., Pennsylvania 19104, USA
2Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA
3USGS-Biological Resources Division, Western Ecological Science Center, 160 N. Stephanie St., Henderson, Nevada 89074, USA
4Present address: Academic Resource Center, Duke University, PO Box 90694, Durham, North Carolina 27708, USA
*Corresponding author: Email:

ABSTRACT: Eight desert tortoises Gopherus agassizii from a long-term mark–recapture study in the Mojave Desert, Nevada, USA, afforded an opportunity to examine the accuracy of skeletochronological age estimation on tortoises from a seasonal, yet environmentally erratic environment. These 8 tortoises were marked as hatchlings or within the first 2 yr of life, and their carcasses were salvaged from predator kills. Using a blind protocol, 2 skeletochronological protocols (correction-factor and ranking) provided age estimates for a set of 4 bony elements (humerus, scapula, femur, ilium) from these tortoises of known age. The age at death of the tortoises ranged from 15 to 50 yr. The most accurate protocol—ranking using the growth layers within each of the 4 elements—provided estimates from 21 to 47 yr, with the highest accuracy from the ilia. The results indicate that skeletochronological age estimation provides a reasonably accurate method for assessing the age at death of desert tortoises and, if used with a large sample of individuals, will provide a valuable tool for examining age-related mortality parameters in desert tortoise and likely in other gopher tortoises (Gopherus).

KEY WORDS: Age · Sexual maturity · Skeletochronology · Testudines · Mojave Desert ·North America

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Cite this article as: Curtin AJ, Zug GR, Medica PA, Spotila JR (2008) Assessing age in the desert tortoise Gopherus agassizii: testing skeletochronology with individuals of known age. Endang Species Res 5:21-27.

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