So here's the essence of the Austronesian religion (below). It's a belief that the cosmos is tripartite: the Upperworld, the earth, and the Underworld.
The Upperworld is often symbolized by the sun or the bird or sometimes by fire. The bird is an obvious choice for the ancient Austronesians because of all creatures, they are the only ones that can go back and forth between the heavens and the earth.
The Underworld's typical icon on the other hand is the snake/serpent/naga. But sometimes, the turtle, croc, fish, etc. are also used.
Here's a
related article (when clicked, the article will download). The article is
Beast, Bird, and Fish: An Essay in South-East Asian Symbolism, by Lorenz G. Löffler. But as far as illustration goes, Bernard Sellato's
The Hornbill and the Dragon is perhaps the best.