In the movie, Nobita and Doraemon use the time tree Mochi to travel back in time and catch a big bird Moa, which they believe has been extinct for 500 years. However, they soon realize that the bird was actually a descendant of the Moa and that the species still exists on an island called Beremon Island.
To protect the bird and its habitat from human interference, Nobita and Doraemon go to Beremon Island, where they meet a girl named Patty from the Rokkoro tribe. The Rokkoro tribe is known for their ability to communicate with animals and protect them from harm. They also meet a boy named Chippo, who looks almost identical to Nobita.
The island is protected by a golden beetle named Herakles, who has the power to control time and space. Herakles initially sees Nobita and his friends as a threat to the ecosystem and tries to eliminate them. However, he eventually realizes that they are truly trying to protect the animals and lets them stay on the island.
As they explore the island, Nobita and Doraemon encounter various endangered animals, including a saber-toothed tiger and a woolly mammoth. They realize the importance of protecting these animals and work with Patty and Chippo to save them from extinction.
In the end, Nobita and his friends successfully protect the animals and their habitat on Beremon Island, and they return to the present time with a newfound appreciation for the importance of preserving endangered species.