By Mel White, Author 
Unlike gorillas and chimpanzees, orangutans live mostly solitary lives. They spend nearly all their time in the treetops, they wander widely, and for the most part they inhabit rugged forest or swampy lowlands that’s hard for humans to traverse. As a result, orangutans long remained among the least known of Earth’s large land animals. Only during the last 20 years or so has scientific evidence begun to outweigh speculation as a new generation of researchers has tracked the elusive apes across the islands of Borneo and Sumatra, the only places orangutans live.
In the 1980s and ’90s, some conservationists predicted that orangutans would go extinct in the wild within 20 or 30 years. Fortunately that didn’t happen. Many thousands more orangutans are now known to exist than were recognized at the turn of the millennium.
This doesn’t mean that all is well in the orangutans’ world. The higher figures come thanks to improved survey methods and the discovery of previously unknown populations, not because the actual numbers have increased. In fact, the overall population of orangutans has fallen by at least 80 percent in the last 75 years. It’s indicative of the difficulty of orangutan research that scientist Erik Meijaard, who has long studied the species’ population trends, is willing to say only that between 40,000 and 100,000 live on Borneo. Conservationists on Sumatra estimate that only 14,000 survive there. Much of this loss has been driven by habitat destruction from logging and the rapid spread of vast plantations of oil palm, the fruit of which is sold to make oil used in cooking and in many food products.
There’s another factor at work as well. A 2013 report by several top researchers said that as many as 65,000 of the apes may have been killed on Borneo alone in recent decades. Some were killed for bush meat by people struggling to survive. Others were shot because they were raiding crops–or protecting their young. The expressive, heart-melting faces of baby orangutans make them highly valuable in the black-market pet trade, within Indonesia as well as smuggled out of Borneo or Sumatra to foreign destinations. The ferocious protectiveness of female orangutans means that the easiest way to obtain a baby is to kill the mother–a compounded tragedy that not only removes two animals from the wild but also eliminates the additional offspring the female would produce during her lifetime.
 National Geographic, Dec 2016