They have named the bird a Cambodian tailorbird. The picture of the little guy that I show here is just a cousin of the Cambodian tailorbird.
Tailorbirds are warblers. They have pretty songs. They are called tailorbirds because they carefully weave their nests in the same way a tailor might make your clothes.
So how do they know that this tailorbird is a different species? Observation was first. It didn't look quite like the others.
They listened. The song of the Cambodian tailorbird is distinctly different from other tailorbirds.
They examined feathers. Feathers from tailorbirds have similarities. But each species has differences from other species of the same family.
They tested DNA samples. The results of all these tests prove that the new species was found.