
These are species with at least one recorded territory in Australia, not a national checklist: a bird list from eBird or Avibase is more complete. The counts follow recording effort as much as wildlife, so a country with more visitors and more naturalists will show more of both.
The species with the most open occurrence records in Australia, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.

Gymnorhina tibicen

Trichoglossus moluccanus

Grallina cyanoleuca

Manorina melanocephala

Hirundo neoxena

Malurus cyaneus

Rhipidura leucophrys

Anthochaera carunculata

Anas superciliosa

Cacatua galerita

Vanellus miles

Threskiornis molucca
The reference database has no regions filed under Australia.
The field guide covers Australia on the map, but none of its species have an entry written for them yet.