- Ochre-bellied Flycatcher
- Ochre-breasted Antpitta
- Ochre-breasted Foliage-gleaner
- Ochre-faced Tody-Flycatcher
- Ochre-naped Ground Tyrant
- Olivaceous Woodcreeper
- Olive-backed Pipit
- Olive-backed Woodcreeper
- Olive-capped Warbler
- Olive-green Tanager
- Olive-striped Flycatcher
- Olive Oropendola
- Olive Woodpecker
- Olrog's Cinclodes
- Orange-banded Flycatcher
- Orange-bellied Euphonia
- Orange-billed Sparrow
- Orange-collared Manakin
- Orange-eared Tanager
- Orange-eyed Thornbird
- Orange-winged Amazon
- Oriental Darter
- Oriental Greenfinch
- Oriental Magpie-Robin
- Oriental Pied Hornbill
- Oriental Pratincole
- Oriental Reed Warbler
- Oriental Skylark
- Oriental Turtle Dove
- Oriente Warbler
- Ornate Flycatcher
- Ornate Sunbird
- Ortolan Bunting
- Osprey
- Oustalet's Tyrannulet
- Ovenbird