1. Faculty of Natural Sciences, University of Stirling, Stirling, FK9 4LA, United Kingdom;
2. Institute for Tropical Ecology Research, Centre National de la Recherche Scientifique et Technologique, BP 842, Libreville, Gabon
3. Wildlife Conservation Society, Bronx, New York, NY 10460;
4. Gabon National Parks Agency, BP 20379, Libreville, Gabon;