Analysis of Gopher Tortoise Population Estimation Techniques
Abstract
Estimating threatened and endangered species (TES), population trends is essential to be able to track a species' recovery progress. Natural resources managers on military installations use a wide variety of survey and monitoring methods, with incomplete knowledge toward their accuracy. Using the gopher tortoise (Gopherus polyphemus) as the test case species, this report examines TES population estimation techniques for accuracy. Managers are cautioned to not accept surveys with unchallenged assumptions of total observability of burrows, and to not convert survey results to tortoise numbers utilizing published correction factors that may not be applicable to a local survey site. The versatility of the quadrat (plot) sampling method recommends it as a default technique that can be used in many sampling circumstances with reasonable expectations of accuracy. Strip transects with reasonable estimates of detectability can offer similar utility when habitat conditions make them appropriate. Previous studies comparing burrow survey methodologies have not adequately addressed the issue of detectability, which presents a weakness in current population estimation and total count technique. It is therefore recommended to under-take a rigorous field test of these techniques to remove the detectability weakness.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2005
- Accession Number
- ADA444540
Entities
People
- Joan E. Berish
- John B. Wooding
- Madan K. Oli
- Raymond R. Carthy
- William D. Meyer
Organizations
- Engineer Research and Development Center