Determination of ape distribution and population size using ground and aerial surveys: a case study with orang-utans in lower Kinabatangan, Sabah, Malaysia

Because of the difficulties encountered in detecting many large tropical forest‐dwelling species in their natural habitat, precise figures concerning the distribution, number and trends of many populations remain deficient. In tropical forests, ground surveys are generally carried out by counting objects along straight lines. These counts require a strict compliance with the line‐transect methodology before (proper design of the census), during...