- Oahu Akialoa
- Oahu Oo
- Okinawa Woodpecker
- Olive-backed Quail-Dove
- Olive-backed Sunbird
- Olive-bellied Sunbird
- Olive-brown Oriole
- Olive-headed Lorikeet
- Olive Bushshrike
- Olive Sunbird
- Olive Thrush
- Orange-backed Troupial
- Orange-breasted Sunbird
- Orange-breasted Trogon
- Orange-eared Tanager
- Orange-footed Scrubfowl
- Orange-fronted Barbet
- Orange-headed Thrush
- Orange-tufted Sunbird
- Orange Fruit Dove
- Orange Ground Thrush
- Oriental Dollarbird
- Oriental Dwarf Kingfisher
- Oriental Plover
- Oriental Pratincole
- Oriental Skylark
- Oriental Stork
- Ornate Lorikeet
- Otago Shag
- Ovambo Sparrowhawk