After an hourlong flight across the Java Sea from Jakarta, I landed at Pangkalan Bun, near the southern coast of Borneo, to be greeted by my forest guide, Erwin. The world’s third-largest island and slightly bigger than Texas, Borneo is shared by the Indonesian province of Kalimantan, the Malaysian states of Sabah and Sarawak, and the tiny, oil-rich nation of Brunei.