These are species with at least one recorded territory in Rwanda, 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 Rwanda, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.
Cinnyris venustus
Cossypha heuglini
Pycnonotus barbatus
Passer griseus
Corvus albus
Cisticola chubbi
Crithagra striolata
Ploceus baglafecht
Nectarinia kilimensis
Colius striatus
Terpsiphone viridis
Melaenornis fischeri
The field guide covers Rwanda on the map, but none of its species have an entry written for them yet.