Wing Clipping
Nothing is more beautiful than watching your cockatiel fly.
Nothing is more heartbreaking than watching it fly outside.
I hope that most of us clip wings. I know that some do not. It doesn't hurt, nor is it cruel. I feel it is more cruel for a predator to end up with a 'tiel snack.
I do however, let my babies (of all species) learn to fly and land safely. Once they have mastered that, their wings are clipped. Now, before you show members start getting the feathers raised, remember, we are talking about pet cockatiels. I prefer to clip evenly on both sides; that way the bird can control its descent. Try clipping the first 5 flight feathers. You don't want the bird to drop - just glide gently to the floor. Continue one feather at a time, until the bird cannot gain altitude.
Your bird will need to be clipped again after the next molt. Be careful, sometimes those feathers can sneak up on you. All it takes is 1 feather on each wing for a cockatiel to be able to fly.

(Permission to use images from Kaytee, September 27, 2006.)
When clipping these flight feathers, be careful not to clip any growing feathers. You will recognise these blood feathers from the others since you can see the dark blood area in the shaft. If you are not quite sure you can be your bird's barber, contact your avian veterinarian or local pet shop. Most will do this grooming for you for a nominal charge. Many will give you hands-on experience.