| an echo of (cave-dwelling) | Oilbirds |
| a gaggle of | Old squaws |
| a pitch of | Orioles |
| a split of | Orioles |
| a harvest of (orchard) | Orioles |
| a duet of | Osprey |
| a flock of | Ostriches |
| a pride of | Ostriches |
| a wobble of | Ostriches |
| a stew of | Ovenbirds |
| a (Teacher! Teacher! Teacher!) of | Ovenbirds |
| a brood of | Owlets |
| a bazaar of | Owls |
| a brood of | Owls |
| a diss of | Owls |
| an eyrie of | Owls |
| a glaring of | Owls |
| a hooting of | Owls |
| a looming of | Owls |
| a nest of | Owls |
| a pair of | Owls |
| a parliament of | Owls |
| a sagaciousness of | Owls |
| a silence of (when in flight) | Owls |
| a stare of | Owls |
| a stooping of | Owls |
| a wisdom of | Owls |
| a stable of (barn) | Owls |
| a jail of (barred) | Owls |
| a prohibition of (barred) | Owls |
| a schizpphrenia of (Hawk) | Owls |
| a volery of (little) | Owls |
| a parliment of (long-eared) | Owls |
| a blizzard of (snowy) | Owls |
| a fling of | Oxbirds |
| a parcel of | Oystercatchers |
| a Rockerfeller of | Oystercatchers |
| a stew of | Oystercatchers |