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

Corvus cornix

Larus cachinnans

Larus argentatus

Melanitta nigra

Grus grus

Corvus frugilegus

Clangula hyemalis

Melanitta fusca

Turdus pilaris

Anser serrirostris

Dendrocopos major

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