Methods for wildlife monitoring in tropical forests: Comparing human observations, camera traps, and passive acoustic sensors Bằng Zwerts, JA, Stephenson, PJ, Maisels, F, Rowcliffe, M, Astaras, C, Jansen, PA, van Der Waarde, J, Sterck, LEHM, Verweij, PA, Bruce, T, Brittain, S, van Kuijk, M