Continuity mistake: After the dinosaurs fight against Kong, Dwan falls on a lake and runs away while staring at the dinosaur. Several bangs of hair cover her forehead. A shot later, when King shows up her forehead is hair-free.
Continuity mistake: At the end, planes are attacking Kong on top of the building. They stop when they see Ann up there. At one point she is standing, hugging Kong's arm. The camera angle changes to a wide shot and shows her about ten feet away and standing up from a crouched position.
Answer: They scared them off with their guns. In the scene where they capture Ann to sacrifice her to Kong, Denham and his men come to rescue her and when they start shooting the natives hide. It's never fully explained but the most likely answer is that they are too scared and have even moved villages or are just hiding really well.