All raptors are protected by state and federal conservation laws. You cannot keep a raptor or any part of a raptor without special federal and state permits. This means you can't keep nests, feathers, eggs, eggshells, etc. without permits - you can be heavily fined or even go to jail. This is true no matter how you got the feathers or eggs - even if you just found them. The only exception is that certain Native American peoples may have certain items for religious purposes.
Falconers have permits to keep raptors, and have training in handling and working with the birds.
Falconers are a valuable resource for information on the care and feeding of the birds, and have helped to preserve several species.