- Oak Titmouse
- Ocellated Tapaculo
- Ocellated Turkey
- Ochre-breasted Antpitta
- Ochre-breasted Pipit
- Oilbird
- Olivaceous Woodcreeper
- Olive-capped Coua
- Olive-capped Warbler
- Olive-striped Flycatcher
- Olive-throated Parakeet
- Olive Bee-eater
- One-colored Becard
- Orange-backed Troupial
- Orange-bellied Euphonia
- Orange-bellied Flowerpecker
- Orange-billed Sparrow
- Orange-breasted Bunting
- Orange-breasted Bushshrike
- Orange-chinned Parakeet
- Orange-crowned Warbler
- Orange-footed Scrubfowl
- Orange-fronted Parakeet
- Orange Chat
- Orangequit
- Orchard Oriole
- Oriental Dollarbird
- Oriental Pied Hornbill
- Oriental Skylark
- Oriental Stork
- Oriental Turtle Dove
- Ornate Sunbird
- Osprey
- Osprey (cristatus)
- Otago Shag