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

Crinifer piscator

Turdus pelios

Centropus senegalensis

Streptopelia vinacea

Pternistis bicalcaratus

Laniarius barbarus

Uraeginthus bengalus

Cinnyris venustus

Passer griseus

Pogoniulus chrysoconus

Lamprotornis purpureus

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