A beak grows in length very slowly and rarely needs shortening unless there is a deviation in the way the top and bottom meet, causing a failure of the two to keep each other worn. There are several causes for this to happen, including malformation during development, injury, invasion by infectious agents, like bacteria, fungi, parasites (knemidocoptes mites), or a virus known as psittacine beak and feather disease virus (PBFD). Another reason for overlength beaks is in the case of chronic liver disease. Otherwise, shortening the beak should never be necessary.
The beak also grows in layers outward. These outer layers should normally be kept worn down as the bird rubs its beak on hard, abrasive materials. It is instinct to rub the beak on things in general, but it is learned from other flock members WHAT to rub it on to keep these layers worn. Many domestic parrots end up with these layers building up due to a lack of proper wear. They rub their beak on the perch or the food dish, their owner, etc., but sometimes the surfaces they rub on simply are not abrasive enough to wear the layers down. They tend to develop a “ledge” of outer layer that runs about 2/3 the way down from the cere to the tip. It represents a natural interface where the new lengthening growth seems to come from under these layers. A "polly perch", or similar perch made of an abrasive material like cement often provides a surface suitable for the bird to groom the beak on, but the placement of the perch is important. If you notice the bird rubbing on a certain perch after eating, for example, simply replace that perch with the cement one.
If this “ledge” develops, it can often be “picked” off with a fingernail, if the bird is willing to let you or if you can restrain its head. If it is very thick and is not worn down, it may begin to cause a deviation in the direction and curvature of the lengthening growth of the tip. If it does get thick, then a nail file, or a Dremel grinder may be used to smooth it down. If a Dremel or an electric rotary nail file is used, care must be taken not to keep the grindstone in one place too long, as this can heat up the beak too much and cause damage to the growth-producing layer beneath.
