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

Microcarbo pygmaeus

Pelecanus onocrotalus

Pelecanus crispus

Falco vespertinus

Aythya nyroca

Larus cachinnans

Ardeola ralloides

Coracias garrulus

Chlidonias hybrida

Dendrocopos syriacus

Ichthyaetus ichthyaetus

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