- Ochre-breasted Antpitta
- Oleaginous Hemispingus
- Olive-backed Euphonia
- Olive-backed Woodcreeper
- Olive-bellied Sunbird
- Olive-grey Saltator
- Olive-sided Flycatcher
- Olive Bee-eater
- Olive Sunbird
- Olive Woodpecker
- One-colored Becard
- Opal-crowned Tanager
- Orange-bellied Euphonia
- Orange-billed Babbler
- Orange-billed Nightingale-Thrush
- Orange-billed Sparrow
- Orange-breasted Bushshrike
- Orange-breasted Fruiteater
- Orange-breasted Green Pigeon
- Orange-breasted Sunbird
- Orange-breasted Trogon
- Orange-breasted Waxbill
- Orange-cheeked Parrot
- Orange-chinned Parakeet
- Orange-collared Manakin
- Orange-crowned Oriole
- Orange-fronted Parakeet
- Orange Minivet
- Orange Weaver
- Oriental Darter
- Oriental Magpie-Robin
- Oriental Pied Hornbill
- Oriental Reed Warbler
- Oriental Skylark
- Ornate Flycatcher
- Ornate Sunbird
- Osprey