- Ochre-bellied Flycatcher
- Ochre-throated Foliage-gleaner
- Oilbird
- Oleaginous Hemispingus
- Olivaceous Woodcreeper
- Olive-backed Foliage-gleaner
- Olive-chested Flycatcher
- Olive-crowned Yellowthroat
- Olive-green Tyrannulet
- Olive-grey Saltator
- Olive-naped Weaver
- Olive-sided Flycatcher
- Olive-striped Flycatcher
- Olive Bushshrike
- Olive Sunbird
- Olive Thrush
- One-colored Becard
- Opal-rumped Tanager
- Orange-bellied Euphonia
- Orange-billed Sparrow
- Orange-breasted Bushshrike
- Orange-breasted Falcon
- Orange-breasted Sunbird
- Orange-cheeked Waxbill
- Orange-crowned Euphonia
- Orange-eared Tanager
- Orange-throated Tanager
- Orange-winged Amazon
- Oriole Warbler
- Ornate Flycatcher
- Ornate Hawk-Eagle
- Osprey