
These are species with at least one recorded territory in Cambodia, 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 Cambodia, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.

Geopelia striata

Pycnonotus goiavier

Aerodramus fuciphagus

Pycnonotus conradi

Streptopelia tranquebarica

Rhipidura javanica

Merops philippinus

Cypsiurus balasiensis

Cacomantis merulinus

Coracias affinis

Ardeola bacchus

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