In the course of his WWF survey for rhinos in Sumatra, the author also made a study of orang-utans. He came to the conclusion that the total number in Sumatra is not more than 3500–4500, despite higher figures that have been circulated, and that probably half of these – the animals living in forests outside the nature reserves – are severely threatened. Not only are they hunted and poached, but their habitat is being rapidly destroyed by big timber companies with concessions for clear-felling-15½ million cubic metres of timber were exported in 1973.