- Ochre-naped Ground Tyrant
- Olive-backed Pipit
- Olive-backed Woodcreeper
- Olive Bee-eater
- Olive Thrush
- Orange-bellied Euphonia
- Orange-bellied Flowerpecker
- Orange-bellied Leafbird
- Orange-breasted Bushshrike
- Orange-breasted Sunbird
- Orange-breasted Trogon
- Orange-breasted Waxbill
- Orange-cheeked Parrot
- Orange-fronted Yellow Finch
- Oriental Darter
- Oriental Dollarbird
- Oriental Magpie-Robin
- Oriental Pied Hornbill
- Oriental Reed Warbler
- Oriental Turtle Dove
- Orinoco Goose
- Oriole Blackbird
- Ornate Flycatcher
- Ornate Sunbird
- Ornate Tinamou
- Osprey