What is the purpose of the covered towers?. Is it to prevent wind and so encourage the Orangs to use them? Or structural or both?
It’s both.
The covered towers have a fine mesh (you can just about see through at close range). It provides the orangutans with low level light as they ascend the towers, but prevents them from escaping and from inclement weather.
On my last visit, it was especially windy, so Melur rested at the top of tower for about 10 minutes before deciding whether or not to come out and traverse the wire to the next tower.