- Ocellated Turkey
- Ochraceous Wren
- Ochre-breasted Antpitta
- Olivaceous Piha
- Olivaceous Woodcreeper
- Olive-backed Euphonia
- Olive-bellied Sunbird
- Olive-green Camaroptera
- Olive-grey Saltator
- Olive-naped Weaver
- Olive-streaked Flycatcher
- Olive-throated Parakeet
- Olive Sparrow
- Olive Thrush
- Opal-crowned Tanager
- Opal-rumped Tanager
- Orange-bellied Euphonia
- Orange-bellied Fruit Dove
- Orange-billed Babbler
- Orange-breasted Green Pigeon
- Orange-breasted Sunbird
- Orange-breasted Waxbill
- Orange-cheeked Parrot
- Orange-cheeked Waxbill
- Orange-chinned Parakeet
- Orange-collared Manakin
- Orange-winged Amazon
- Orange Minivet
- Orchard Oriole
- Oriental Darter
- Oriental Magpie-Robin
- Oriental Skylark
- Oriental Turtle Dove
- Orinoco Saltator
- Oriole Blackbird
- Oriole Warbler
- Ornate Flycatcher
- Ornate Melidectes
- Ornate Sunbird
- Ortolan Bunting
- Osprey
- Ovenbird