- Ochraceous Wren
- Olivaceous Piculet
- Olive-backed Euphonia
- Olive-bellied Sunbird
- Olive-breasted Greenbul
- Olive-crowned Yellowthroat
- Olive-green Camaroptera
- Olive-streaked Flycatcher
- Olive-throated Parakeet
- Olive Bee-eater
- Olive Sparrow
- Olive Sunbird
- Orange-billed Babbler
- Orange-billed Sparrow
- Orange-breasted Bushshrike
- Orange-breasted Green Pigeon
- Orange-breasted Waxbill
- Orange-cheeked Waxbill
- Orange-chinned Parakeet
- Orange-collared Manakin
- Orange-headed Thrush
- Orange-tufted Sunbird
- Orange Minivet
- Orchard Oriole
- Oriental Darter
- Oriental Magpie-Robin
- Oriental Skylark
- Oriente Warbler
- Oriole Finch
- Ortolan Bunting
- Osprey
- Ovenbird