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

Turdoides affinis

Pycnonotus cafer

Psilopogon zeylanicus

Corvus splendens

Dicrurus caerulescens

Oriolus xanthornus

Leptocoma zeylonica

Dicaeum erythrorhynchos

Psittacula krameri

Spilopelia chinensis

Ducula aenea

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