- Olive-backed Tailorbird
- Olive-naped Weaver
- Olive-throated Parakeet
- Olive-winged Bulbul
- Olive Bee-eater
- Olive Sunbird
- Olive Thrush
- Orange-breasted Sunbird
- Orange-chinned Parakeet
- Orange-winged Amazon
- Oriental Darter
- Oriental Dollarbird
- Oriental Magpie-Robin
- Oriental Pied Hornbill
- Oriental Pratincole
- Orinoco Goose
- Oriole Warbler
- Ornate Sunbird
- Osprey