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

Sturnus unicolor

Larus michahellis

Serinus serinus

Larus fuscus

Curruca melanocephala

Gyps fulvus

Pica pica

Cettia cetti

Turdus merula

Carduelis carduelis

Galerida cristata
Ciconia ciconia
The reference database has no regions filed under Spain.
The field guide covers Spain on the map, but none of its species have an entry written for them yet.