I haven't seen the thread, but I wonder if the centres are a kind of repository of feathers. There's a process called imping which is used to replace broken or cut feathers. Basically a replacement feather is bonded, using a small rod of bamboo and glue, into the shaft of the broken feather. The replacement feather must be a very very close match to the original and even then, it might not cope with the stresses placed on it during take off, flight and landing.
Repositories exist so that it's easier to find a close match: species, size, the exact placement on the wing and so on are all critical in identifying a suitable match.
This is a short introduction:
The practice has been described by kings, mentioned in Shakespeare, and is regularly performed at rehabilitation clinics everywhere.
www.audubon.org
This is a detailed set of instructions aimed at vets
