Dung survey bias and elephant population estimates in southern Mozambique

We used dung surveys to estimate population size and extracted an age structure from boli diameters for the elephants living in the Maputo Elephant Reserve. Our estimate was based on published defecation rates, dung decay rates, distance-sampling techniques and 1,672 dung piles encountered on 204 line-transects. The reserve had at least 311 (95% CI: 198–490) elephants at a density of 0.60 (95% CI: 0.38–0.94) per km. However, observer bias reduced effective strip widths and inflated estimates and their confidence limits. The age structure extrapolated from dung measurements indicated few newborn calves compared with other populations. To detect population changes of 2–5% at 80% power, dung surveys should be carried out every second year for the next 20 years using 100 transects of at least 500 m each. Comparison with a 1995 dung survey suggests that the population is stable and that previous fears of a major population decline during the civil war have no foundation.