moulting

Depending on the species, feathers comprise between 15% and 20% of a bird's body weight. see Caring for your Lovebirds & Foreign Parrots (African Lovebird & Foreign Parrot Soc of Qld Inc)

Growing feathers are often called "blood feathers" - each feather has its own blood supply until it finishes growing. If a feather is damaged after its blood supply is cut off, it cannot repair itself and can be replaced only in the next moult.

To compensate for the energy lost during moulting, a healthy bird's metabolism usually prevents the bird's body from carrying out two stressful functions - e.g. laying eggs and moulting - at the same time.

During the moult, feathers become loose as the feather follicles in the skin become active and engorged with blood. New feathers are being formed, and they push out the old ones. The primary purpose of moulting is to replace old, worn-out feathers with new ones. The feather growing process requires a great deal of energy, so birds usually sign less during moults. Most moults begin with the loss of the innermost primary feathers on both wings. When about half the primaries are affected, the moult continues to the outermost secondary feathers on the wings. The bird then begins to moult its body feathers, followed by its tail feathers. The reason for this sequence is so the bird can retain its flying ability during all stages of its moult . ©