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Manipulating decay time for efficient large-mammal density estimation: gorillas and dung height
Hjalmar S Kuehl1, Angelique Todd, Christophe Boesch
1Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig 04103, Germany. kuehl@eva.mpg.de
Summary
Estimating large mammal populations using dung decay rates can be biased. New methods using dung height offer a more precise and efficient approach for wildlife surveys.
Area of Science:
- Ecology
- Wildlife Management
- Conservation Biology
Background:
- Large mammal population estimates often rely on indirect signs like dung.
- Translating sign density to animal density requires accurate sign production and decay rates.
- Current decay rate estimation methods can be spatially biased due to extensive travel effort.
Purpose of the Study:
- Evaluate bias from extrapolating decay rates from unrepresentative locations.
- Assess effort required for spatially unbiased decay rate estimation.
- Explore alternative methods for improving precision in wildlife density estimates.
Main Methods:
- Collected gorilla dung data at central African sites to assess decay rate variation.
- Estimated effort-precision relationships for retrospective decay rate (RDR) and marked sign count (MSC) methods.
- Examined dung height as an objective criterion for decay.
Main Results:
- Gorilla dung decay rates showed enormous variation (up to an order of magnitude).
- Both RDR and MSC methods require substantial effort for precise density estimates.
- Dung height as a decay criterion significantly improves RDR efficiency by reducing necessary site visits.
Conclusions:
- Spatially unbiased estimation of decay rates is crucial for accurate wildlife density.
- Objective criteria like dung height can enhance the efficiency of decay rate methods.
- A prospective decay rate (PDR) approach using objective criteria shows promise for significant precision increases, warranting further research.
