In The Island of the Blue Dolphins, how does Rontu die?

After many years, Rontu returns to the cave where he used to live with his pack. Karana tracks him there, and notices that he is very weak, hardly breathing. She carries him to the cliffside, hoping that he will revive himself when he sees the gulls he always liked to chase. However, he dies. Devastated, Karana gives him a beautiful burial. After Rontu’s death, she stops keeping track of how long she has been on the island.

We can infer that Rontu died of old age.... natural causes.