A half-clipped feather will allow more upward flight, and will necessitate the removal of more feathers to restrict flight than a technique that removes the entire feather. Cockatiels are powerful fliers and may often need six to eight feathers trimmed on each wing. Budgies will also usually require trimming of about six primaries. As a rule, overweight or heavy bodied birds need fewer feathers removed than birds of normal weight or trim bodies. Overweight Amazons may only require about four or five feathers per wing removed.
Amazons drop heavily if too many feathers are taken and often sustain injuries.
Cockatoos, which are usually leaner birds, often require seven primaries be removed. Conures and other small bodied, long tailed birds may require five to seven feathers clipped. Each bird should be conservatively trimmed and more feathers taken if necessary after flight testing, as previously described. The individual bird's ability to fly will vary. Most avian veterinarians and aviculturists agree that both wings should be symmetrically trimmed.