Studying a Species in Decline: Gopher Tortoises and the Dilemma of "Correction Factors"

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Burrow, Correction factor, Gopher tortoise, Gopherus Polyphemus, Habitat, Population estimates


Numbers of gopher tortoises are declining throughout the southeastern United States, largely because of loss of habitat. Widespread monitoring of population sizes for gopher tortoises usually is done indirectly, by examining the burrows that tortoises construct. Indirect monitoring requires use of a correction factor, to relate numbers of burrows to numbers of tortoises. We demonstrate that the standard correction factor overestimates the number of tortoises in 22 of the 26 cases in our sample and that the relationship between numbers of burrows and numbers of tortoises differs among types of habitats. Using both published data and data from our own studies, we suggest that an accurate assessment of active burrows is a reliable way to relate numbers of burrows to numbers of tortoises.

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Herpetologica, v. 48, issue 4, p. 402-407