Appears to the either the 5th book or the final book

The book Sky Fire by Erin Hunter, is about four bear cubs, Kallik, a polar bear, Toklo, a brown bear, Lusa, a black bear and Ujurak, a shape shifting brown bear. The group of bears were in the Last Great Wilderness, when flat-faces, or humans, started drilling for oil. Then the bears had to venture onto the ice to find something they didn’t know they were looking for. Later Lusa’s going through the long sleep, or hibernation, and it starts getting harder for them to continue. They continue their trek on the ice until they all have a dream where they are visited by their mothers where they are told advice. Toklo says that he was going to take Lusa back to the forest because he got a warning in his dream that one of them would die before they reached their destination, and he was worried that it would be Lusa. So Toklo and Lusa went their own way, while Ujurak and Kallik continued to where the sun sets on the ice. While on their way, Toklo and Lusa get trapped in an oil reserve and Lusa is taken by the flat-faces. While that happened Kallik and Ujurak have a dream and feel like Lusa or Toklo might be in trouble. So when they get there Ujurak is told to change into a human to get Lusa out of the flat-face den. So they get Lusa out of there and they continue.
This author had a good way of transitioning from one set of characters to another. Also I liked how the author had every chapter have a character’s thoughts and actions. The author had very creative names for every day human stuff like fire-beast for car and firesticks for guns.