- Oak Titmouse
- Ochraceous Bulbul
- Ochre-breasted Antpitta
- Olivaceous Piculet
- Olive-backed Euphonia
- Olive-backed Pipit
- Olive-grey Saltator
- Olive-winged Bulbul
- Olive Bee-eater
- Olive Bulbul
- Orange-bellied Euphonia
- Orange-bellied Flowerpecker
- Orange-bellied Leafbird
- Orange-billed Nightingale-Thrush
- Orange-billed Sparrow
- Orange-breasted Trogon
- Orange-cheeked Waxbill
- Orange-chinned Parakeet
- Orange-crowned Warbler
- Orange-fronted Parakeet
- Orchard Oriole
- Oriental Darter
- Oriental Magpie-Robin
- Oriental Pied Hornbill
- Oriental Pratincole
- Oriental Reed Warbler
- Oriental Turtle Dove
- Ornate Sunbird
- Ortolan Bunting
- Osprey
- Ovenbird