Population Survey

This dataset comprises dung count line transect data from a survey conducted in the Ngombé Ntokou-Pikounda forest, Republic of the Congo, in Feb - Oct 2014. The survey estimated an elephant population of 4 142 (95% c.i. 2 994 - 5 731) within the 16 190 km² survey area. Elephant numbers in the landscape appear to have declined, but not significantly, since the last survey in 2007 (this previous survey had wider confidence limits in estimated elephant numbers). A total of 427.4km of transects were walked in 6 strata (Ngombe NW: 22 x 2km transects, 43.7km total, Ngombe Road corridor: 30 x 2.5km transects, 74.9km total, Ngombe Sangha E: 32 x 2.5km transects, 77.7km total, Ngombe south-centre: 32 x 2km transects, 63.1km total, Ngombe SW: 33 x 2.5km transects, 82.1km total, Ntokou-Pikounda and Pikounda N: 43 x 2km transects, 85.9km total). Dung density was recorded as Ngombe NW: 622 (95% c.i. 436-888) per km² with 2.77 (95% c.i. 1.94-3.94; CV 17.27%) encountered per km, Ngombe Road corridor: 588 (95% c.i. 245-1410) per km² with 2.62 (95% c.i. 1.09-6.27; CV 44.80%) encountered per km, Ngombe Sangha E: 64 (95% c.i. 24-170) per km² with 0.28 (95% c.i. 0.11-0.76; CV 51.12%) encountered per km, Ngombe south-centre: 310 (95% c.i. 169-567) per km² with 1.38 (95% c.i. 0.75-2.52; CV 30.35%) encountered per km, Ngombe SW: 881 (95% c.i. 627-1239) per km² with 3.92 (95% c.i. 2.80-5.50; CV 16.87%) encountered per km, and Ntokou-Pikounda and Pikounda N: 374 (95% c.i. 240-583) per km² with 1.66 (95% c.i. 1.07-2.59; CV 22.24%) encountered per km. Elephant populations were estimated as Ngombe NW: 329 (95% c.i. 230-469), Ngombe Road corridor: 1299 (95% c.i. 542-3116), Ngombe Sangha E: 80 (95% c.i. 30-213), Ngombe south-centre: 457 (95% c.i. 250-837), Ngombe SW: 837 (95% c.i. 595-1176), Ntokou-Pikounda and Pikounda N: 1141 (95% c.i. 732-1777). Dung production and decay rates were used from MIKE 2005 (values of 19 and 90 respectively). To improve the precision of the current study the number of transects were increased from 78 transects undertaken in 2007 to 192 in 2014; and the strata were changed to better reflect areas where wildlife densities were likely to be less heterogenous within each stratum. To improve accuracy, total effort was increased by increasing the length of each replicate (transect) from 1 to 2 or 2.5 kilometres, in order to capture more objects (mammal dungpiles and ape nests) than in 2007. *** Data capturer notes: *** The survey area has changed slightly since 2007, but the authors re-analysed the 2007 data using the current spatial footprint when making direct comparisons. The same dung deposition and decay rate parameters were used as in 2007. The authors note that all but one of the planned transects were completed (192 are listed); the missing transect was not included in the counts for each strata.