This is the 3285th most frequent Russian word.
остров
Island.
In this sentence, 'остров' is used to denote a geographical entity, specifically the island of Bali.
Я мечтаю посетить остров Бали.
I dream to visit the island of Bali.
Here, 'острове' is the declinated form of 'остров' in the prepositional case, indicating the location of the birds.
На острове обитает множество редких птиц.
Many rare birds inhabit the island.
In this sentence, 'остров' emphasizes a self-contained landmass separated from a larger area.